Final Report Summary - HAMLET (Human ModeL MATROSHKA for Radiation Exposure Determination of Astronauts)
Executive Summary:
To quote Seneca's Megara, Hercules' wife, saying: "Non est ad astra mollis e terra via" - the road for humans to travel to the stars is posing manifold challenges. Among all obstacles one has to solve to work and live in space, such as adverse physiological effects of microgravity and psychosocial concerns related to the stresses of confined isolation and interpersonal dynamics, the probably biggest threat to human health is posed by cosmic rays, especially when thinking of long-term missions of exploration. The radiation load on space travellers in low-Earth orbit, like on the International Space Station (ISS), is a factor of ~100 higher than the natural radiation exposure on ground, and it will further increase should humans return to the Moon or travel to Mars in the future. The risks associated with exposure to space radiation have to be determined as accurately as possible in order to support safe human exploration of the solar system. One way to quantify these risks is by measuring the radiation doses to vital organs of the human body inside human-like phantoms, as performed through the ESA facility MATROSHKA (MTR) on board the ISS. MATROSHKA houses an anthropomorphic phantom torso and is operated under the scientific project lead of the German Aerospace Center (DLR). The experiment is dedicated to determining the radiation exposure of astronauts when staying inside or outside the space station. The phantom is equipped with more than 6,000 radiation detectors to measure the depth dose and organ dose distribution in the body. It is the largest international research initiative ever performed in the field of radiological protection in space and combines the expertise of leading scientific institutions around the world, thereby generating a huge pool of data of potentially immense value for research. MATROSHKA was launched to the ISS in January 2004. Up to March 2011, four missions have been accomplished. During the MTR-1 experimental phase (2004-2005) the facility was installed outside the Russian Service Module (Zvezda) simulating a long-duration astronaut space walk. The MTR-2A experimental phase was carried out in the year 2006 inside the Russian docking compartment (Pirs). The third phase (MTR-2B) in the years 2007 to 2009 saw the phantom mounted inside Zvezda, followed by a fourth exposure inside the Japanese Experiment Module from 2010 to 2011 (MTR-2 Kibo). The FP7 project HAMLET (Human Model MATROSHKA for Radiation Exposure Determination of Astronauts, http://www.fp7-hamlet.eu aimed at the effective scientific exploitation of data obtained from the ESA MATROSHKA experiment. This was achieved by bringing together leading European scientists in the field of space dosimetry to increase and enhance the output of the project and present it to the European scientific community as well as the public audience. The HAMLET project focused on the detailed analysis, compilation and comparison of the data generated by the MATROSHKA experiment for the development of a three-dimensional model of the dose distribution inside a human body, both simulating an astronaut's space walk and an astronaut working at different locations inside a space station. The developed model has been verified and benchmarked using complex Monte Carlo radiation transport codes. Further, an extensive ground-based programme has been initiated at diverse heavy-ion accelerator facilities around the world to determine the response and characteristics of the radiation detectors used within the MATROSHKA project. These data serve as benchmark against radiation transport codes and further supported verification of the accuracy of the developed dose-distribution model. The outcome of the work performed within HAMLET enabled the determination of the effective dose in and outside the space station, contributed to improved radiation risk assessment for long-duration spaceflight and greatly helped securing the future safe presence of humans in low-Earth orbit and beyond.
Project Context and Objectives:
HAMLET - Mission Statement
The aim of HAMLET (http://www.fp7-hamlet.eu) is the effective scientific exploitation of data obtained from the ESA MATROSHKA project. This will be achieved by bringing together leading European scientists in the field of space dosimetry to increase and enhance the output of the project and present it to the European scientific community as well as the public audience.
(See: Figure Summary-0: FP7 HAMLET LOGO)
HAMLET - Context
The radiation exposure in space is a limiting factor, especially when thinking of long-term human presence in space. The radiation load on space travellers in low-Earth orbit, like on the International Space Station (ISS), is a factor of ~100 higher than the natural radiation exposure on ground, and it will further increase should humans return to the Moon or travel to Mars. The health risks associated with exposure to cosmic radiation have to be determined as accurately as possible in order to support safe human exploration of space. One way to quantify these risks is by measuring the radiation doses to vital organs of the human body inside human-like phantoms, as performed through the ESA facility MATROSHKA (MTR) on board the ISS. MATROSHKA is a mannequin equipped with more than 6,000 radiation sensors to allow assessing the exposure of a simulated astronaut's torso to cosmic radiation. The facility was launched to the ISS in January 2004. Up to March 2011, four missions have been accomplished. During the MTR-1 experimental phase (2004-2005) the facility was installed outside the Russian Service Module (Zvezda) simulating a long-duration astronaut space walk. The MTR-2A experimental phase was carried out in the year 2006 inside the Russian docking compartment (Pirs). The third phase (MTR-2B) in the years 2007 to 2009 saw the phantom mounted inside Zvezda, followed by a fourth exposure inside the Japanese Experiment Module from 2010 to 2011 (MTR-2 Kibo).
(See: Figure Summary-1: MATROSHKA-1; Table Summary-1: MATROSHKA-1)
(See: Figure Summary-2: MATROSHKA-2A; Table Summary-2: MATROSHKA-2A)
(See: Figure Summary-1: MATROSHKA-2B; Table Summary-3: MATROSHKA-2B)
HAMLET Project Goals and Project Objectives
To ensure the optimal scientific exploitation of the data generated within the MATROSHKA experiment, the FP7 collaborative project HAMLET (1 September 2008 - 30 September 2011) brought together European experts to process and compile the acquired data and develop a three-dimensional model of the distribution of radiation dose in an astronaut's body. The overall project goals for HAMLET were the following:
* Compilation of data sets from MTR-1, MTR-2A and MTR-2B
This compilation includes the contribution of the European partners (who provided almost 90% of the scientific data) as well as the non-European partners in the MATROSHKA project. The comprehensive inter-comparison and compilation of experimental data acted as input for the proposed radiation transport calculations. The European partners within the HAMLET consortium have extensive experience in either experimental assessment or numerical modelling of the space radiation environment. The group therefore brought together experimental and theoretical researchers working on the common goal of exploring and deepening our knowledge of space radiation effects on the human body.
* Data archive
Strongly interlinked with the data compilation, the build-up of a data archive enabled the community to access the measured and evaluated data from all participating laboratories. This was essential for the achievement of the project goals as it improved the scientific results by incorporating the individually collected data sets into an overall context. This effort permitted straightforward data access and comparison.
* 3D radiation model
A three-dimensional (3D) numerical model of the space radiation dose distribution within the phantom torso has been developed based on experimental data sets. In parallel, a three-dimensional model has been derived from Monte Carlo radiation transport calculations and verified against measurements. This will enable future simulations of tissue and organ doses for radiation risk assessment of personnel on long-term space missions on the ISS, to the Moon or other celestial bodies.
* Public awareness
The presentation of scientific data to the public was strongly emphasized within the project. Raising the public's awareness and understanding, particularly in the well-debated field of health physics and radiological protection, was an essential task. The MATROSHKA experiment gave us a perfect 'tool' by connecting the issues of 'space radiation' and 'radiation received on human missions to the Moon and Mars' with the human perspective, particularly since MATROSHKA is meant to simulate an astronaut in the space environment. This context along with the possibility of generating a 3D dose distribution throughout the human body, was taken as input for the development of public outreach activities, including a public version of the data archive.
According to these goals, the overall objectives were defined as (1) the processing, compilation and combination of dosimetric data from the MATROSHKA experiment; (2) the characterization of the radiation detector response to a well-defined subset of the space radiation environment and harmonization of experimental protocols; (3) the survey and detailed exploitation of available literature on cosmic-ray dosimetry on board the ISS and phantom experiments in space; (4) the development of a three-dimensional voxel model of the MATROSHKA phantom to facilitate the calculation of organ doses and thereby assessing the effective dose as a prerequisite for radiation risk estimation; (5) radiation transport calculations using the Monte Carlo transport code PHITS; (6) the launch of a dedicated HAMLET website and build-up of a database structure for archiving MATROSHKA dosimetric data and (7) the organization of HAMLET Public Outreach Events to inform the public audience about the status of the project.
Within the HAMLET project, these objectives were embedded in five dedicated work packages (WP), with corresponding milestones and deliverables: WP1: Data Processing and Compilation; WP2: Detector Characterization; WP3: ISS Space Data Intercomparison; WP4: Experimental and Calculated 3D Radiation Model; WP5: Dissemination of Results.
* Work Package 1: Objectives
The overall goal of Work Package 1 of the HAMLET project was the compilation and combination of radiation detector data gathered by all groups from the MTR-1, MTR-2A and the MTR-2B experimental phases. These data sets were used as essential input for the development of a 3D model on the basis of measured data and serve as benchmark for the applied data radiation transport codes. The data evaluation and processing was performed both for data generated with passive radiation detectors during all the three mission phases as well as for data generated with active radiation detectors measured during the MTR-1 and the MTR-2B mission phase.
* Work Package 2: Objectives
The aim of Work Package 2 was to characterize the detector systems applied within the MATROSHKA experiment, in terms of their detection properties. Detector characterization was needed in two respects. The first concerned the peculiarity of the conditions encountered by detectors within the MATROSHKA experiment, that is, the complexity of the radiation field and a very long time of exposure. The second requirement for detector characterization came from the great variety of radiation detectors that have been used within the experiment. Each investigator further applied his own measurement and calibration protocols. It was therefore essential to compare performance of detectors and evaluation procedures applied by the individual participants. The main effort of Work Package 2 activities was in characterization of radiation detectors in ground-based radiation fields available from high-energy particle accelerators, which may be considered as a simulation of sub-sets of the space radiation environment. The HAMLET consortium was granted with two research projects by the National Institute of Radiological Sciences (NIRS) in Chiba, Japan, and the ESA European Space Research and Technology Centre (ESTEC) in Nordwiijk, The Netherlands, for using machine time at the Heavy Ion Medical Accelerator (HIMAC) in Chiba and the Heavy-Ion Synchrotron (SIS) of the GSI Helmholtz Centre for Heavy-Ion Research in Darmstadt, Germany. Within the realized five irradiation campaigns at the HIMAC and two at GSI, the detectors were exposed to monoenergetic beams of fully ionized helium, carbon, silicon, neon, argon, iron and nickel nuclei with energies up to 1000 MeV/u.
* Work Package 3: Objectives
Interpretation of the comprehensive MATROSHKA data set compiled within Work Package 1 required putting the scientific output in the context of other research in the field of cosmic radiation dosimetry conducted in parallel with the MATROSHKA experiment. Having analysed the detection principles and response characteristics of the vast suite of active and passive instrumentation previously or currently applied in space, the published scientific literature on phantom studies in space as well as active and passive radiation monitoring conducted on board the ISS from 2004 to present has been reviewed in detail and, finally, compared with the MATROSHKA dosimetric results in order to evaluate their relevance for radiation exposure assessment of astronauts.
* Work Package 4: Objectives
The aim of Work Package 4 was the build-up of a 3D model of the MATROSHKA results based on the data generated within Work Package 1 and the calculation of the dose values within the phantom using Monte Carlo transport codes. As a prerequisite for the numerical model, two computer tomography (CT) scans of the MATROSHKA have been performed. The data from the CT scans were then used to build a voxel model called NUNDO (Numerical RANDO) of the phantom. A computer program OrDoCal (Organ Dose Calculation) was developed for the interpolation of point doses over the whole phantom volume and for calculation of the organ doses based on the data input from Work Package 1. Using this software, the data obtained within the three MATROSHKA experimental phases were analysed and a 3D dose distribution based on the measurements within the phantom was calculated. This 3D dose distribution model enabled determination of effective dose for the three missions and thereby supported for radiation risk estimations. The radiation transport calculations for the MTR-1 and the MTR-2B experimental phases were performed using the three-dimensional multi-purpose particle and heavy-ion Monte Carlo transport code PHITS coupled to the developed voxel phantom NUNDO. For the MTR-1 simulations, the phantom, together with the container, was placed on the aluminium foundation and the inside of the foundation as well as the inside of the container were filled with air. The container together with the foundation, were located on a simplified ISS geometry, represented by an aluminium cylinder. Organ dose and dose equivalent rates were calculated in the NUNDO phantom. Simulations of the MTR-2B experiment inside the ISS were performed in the same way. Simulations of irradiations of the MATROSHKA phantom head at the HIMAC were obtained using the Monte Carlo code packages FLUKA and GEANT4.
* Work Package 5: Objectives
The overall goal of Work Package 5 is the dissemination of results of the HAMLET project. The public outreach of HAMLET was optimized by installation of the HAMLET webpage under http://www.fp7-hamlet.eu. The scope of this page was not only to inform the public about the project itself, but also provide a comprehensive, still concise overview of the space radiation environment, detector instrumentation, numerical modelling and associated topics, and highlight the expertise of the participating institutions. An image gallery serves as an online repository of digital images pertaining to the MATROSHKA experiment and HAMLET activities. Five dedicated Public Outreach Events, hosted and organized at the bases of the participating institutions, helped to further increase the awareness of the public audience to the significance of radiation exposure in view of the future development of human spaceflight. The science achievements of the HAMLET project were disseminated publicly through a web database. Following the definition of a unified structure for the experimental data provided by the individual participants, a front end of the web database has been designed which allowed for convenient and reliable uploading of the processed dosimetric data under http://www.fp7-hamlet.eu/index.php/database. The data archive currently contains absorbed dose rates measured under extravehicular activity (EVA) conditions during the MTR-1 experiment by miniature luminescence detectors at about 4,800 sites within the anthropomorphic phantom body. The user is graphically assisted in navigating through the torso. The database will be updated upon publication of the final results of the HAMLET project.
Project Results:
Introduction
The astronauts and cosmonauts working and living in a space station at altitudes of ~400 km are exposed to radiation levels far exceeding the natural radiation environment on ground. The three main radiation components in low-Earth orbit (LEO) are galactic cosmic rays (GCR), emissions from the Sun - either solar particle events (SPE) or coronal mass ejections (CME) - and protons and electrons trapped in the Van Allen belts. In LEO, albedo neutrons and protons can also be found that are produced when GCR particles interact with the atmosphere and travel along trajectories reflecting them back into space. The contribution of these sources to the radiation load on humans on board a space station varies greatly and depends on various parameters such as the orbital inclination and altitude, the shielding distribution of the spacecraft and the solar cycle. Contrary to the radiation environment on Earth, the main contribution to the radiation exposure arises from heavy charged particles encountered in GCR and protons emitted by the sun. Due to their high energies, these primary particles can easily penetrate a spacecraft wall, thereby creating a secondary radiation field, which includes neutrons. The radiation load on humans in space can therefore reach levels that are up to a factor of 100 times greater than those present on Earth, giving the space-faring nations a legal and moral obligation to monitor the radiation exposure of space travellers, particularly for long-duration missions. Data from active and passive radiation monitoring act as input for risk estimates of cancer induction, attributed to the high radiation level. Since the internal organs of the human body are more sensitive to penetrating radiation than the skin, the determination of organ doses is an essential aspect. Measurements are only possible by applying anthropomorphic phantoms that allow integration of radiation detectors inside a simulated human body.
The Radiation Biology Department of DLR developed the anthropomorphic phantom experiment MATROSHKA. The MATROSHKA facility is an ESA experimental unit for studies of the depth dose distribution through the different components of the LEO radiation field at the sites of specified organs. MATROSHKA consists of a human head/torso phantom, allowing accommodation of dedicated active and passive radiation measurement devices. The objective of the MATROSHKA experiment is to determine the empirical relations between measurable and tissue absorbed doses in a realistic human phantom exposed to cosmic radiation. Such measurements have the highest priority, particularly in view of long-term human space exploration. Once the ratio between surface and tissue/organ doses is known for a particular radiation field, it may be used in future exposures to determine the required tissue/organ doses from measurements of just the surface dose, which are much easier to perform. The collected data will be used to reduce the uncertainties of risk projections of radiation-induced cancer and to refine shielding structures in future space missions.
The MATROSHKA facility basically consists of a human phantom upper torso, a base structure and a container with a total mass of about 65 kg. The phantom torso and container are mounted to the base structure, which serves as a footprint for the human mannequin. The container consists of a carbon fibre structure, forms together with the base structure a closed volume which is filled with a dry oxygen atmosphere at ambient pressure and protects the phantom against space vacuum, debris, solar UV and material off-gassing. It provides approximate the same shielding thickness as an Astronaut's space-suit does. The phantom body is made of natural skeleton embedded in tissue equivalent polyurethane w of different densities for tissue and lungs, well introduced in the field of radiotherapy. It consists of 33 slices, each with a thickness of 25 mm. The phantom slices are equipped with channels and cut-outs to allow the accommodation of active and passive dosemeter systems as well as temperature and pressure sensors (housekeeping data). A total number of six temperature sensors, three of them in the phantom torso at slices #2 (head), #16 (upper torso) and #26 (lower torso) and three in the base structure as well as two pressure sensors allow recording of temperature and pressure profiles in the facility. Besides the dose determination inside the body, the torso is also equipped with a poncho and a hood equipped with radiation detectors for skin dose measurements. The cables indicate the positions of the silicon scintillation detectors (SSD) at selected organ sites. A DOSimetry TELescope (DOSTEL) is mounted on top of the head, while a tissue -equivalent proportional counter (TEPC) is installed in front of the upper body on the base structure.
The 33 slices of the phantom are equipped with 356 channels for accommodation of thermoluminescence dosemeters (TLDs) from the participating groups at a total of 1634 positions arranged in a one-inch grid throughout the body. The TLD chips are kept in tubes with tissue-equivalent spacers. At each of the 1634 points, between two and six dosemeters of different thermoluminescence (TL) phosphors are located, e.g. a combination of 6LiF:Mg,Ti, 7LiF:Mg,Ti and 7LiF:Mg,Cu,P. Besides determination of the absorbed dose, this configuration also permits information about the thermal and epithermal neutron dose to be obtained using the so-called pair method. Except for the TLDs contained in the 33 slices, the phantom has five cut-outs for installation of nuclear track detector packages (NTDP), sized 55 x 35 x 21 mm, to measure the absorbed dose to the eye, lung, stomach, kidney and intestine. Each of these boxes is equipped with a combination of sixty TLDs and plastic nuclear track detectors (PNTDs), the latter being arranged orthogonally to enable assessment of linear energy transfer (LET) and charge spectra in three perpendicular axes. Further, the packages contain PNTDs covered by converter foils to evaluate the neutron organ doses. The poncho and the hood are equipped with polyethylene stripes with sewed-in TLDs to measure the skin dose around the entire torso. The poncho is further equipped with six NTDP packages in similar dimensions as used at organ sites (two in the front, two in the back and one on each side of the torso) to support the skin dose measurements. On top of the phantom head a NTDP as well as the silicon telescope DOSTEL are located. Inside the torso, at the sites of particular organs active SSDs (plastic scintillators covered by silicon diodes operated in anti-coincidence mode) are placed next to an NTDP.
(See: Figure Introduction-1: MATROSHKA-Facility)
(See: Figure Introduction-2: MATROSHKA-Detectors)
To ensure the optimal scientific exploitation of the data generated within the MATROSHKA experiment, the FP7 collaborative project HAMLET (1 September 2008 - 31 August 2011) brought together European experts to process and compile the acquired data and develop a three-dimensional model of the distribution of radiation dose in an astronaut's body. In particular, the project objectives were (1) the processing, compilation and combination of dosimetric data for the MATROSHKA experiment; (2) the characterization of the applied radiation detector response to a well-defined subset of the space radiation environment and harmonization of experimental protocols; (3) the survey and detailed exploitation of available literature on cosmic-ray dosimetry on board the ISS and phantom experiments in space; (4) the development of a three-dimensional voxel model of the MATROSHKA phantom to facilitate the calculation of organ doses and assess effective dose as a prerequisite for radiation risk estimations; (5) radiation transport calculations using the Monte Carlo transport code PHITS; (6) the launch of a dedicated HAMLET website and build-up of a database structure for archiving MATROSHKA dosimetric data and (7) the organization of HAMLET Public Outreach Events to inform the public audience about the status of the project.
The main scientific results of the HAMLET project, embedded in five dedicated work packages (WPs) with corresponding milestones and deliverables (WP1: Data Processing and Compilation; WP2: Detector Characterization; WP3: ISS Space Data Intercomparison; WP4: Experimental and Calculated 3D Radiation Model; WP5: Dissemination of Results) will be outlined in the following sections.
WP1: Data Processing and Compilation
The overall goal of Work Package 1 of the HAMLET project was the processing, compilation and combination of data acquired by the participating laboratories from TLD and PNTD measurements during the MTR-1, MTR-2A and MTR-2B experimental phases. These data sets were used as essential input for the development of a 3D model on the basis of measured data and serve for benchmarking the radiation transport codes (see also Work Package 4). In addition Work Package 1 was devoted to the analysis of data generated with the active radiation detectors during the MTR-1 and MTR-2B experiment phase.
Thermoluminescence detectors: For the determination of the absorbed dose from ionizing radiation the HAMLET collaboration applied passive TLDs of various types. The energy deposited by ionizing radiation in these detectors is stored at defect centres in the crystal lattice and released in the form of light upon heating in the laboratory (readout) yielding the so-called glow curve. The emitted light is proportional to the absorbed dose, thus enabling TLD utilization in radiation dosimetry upon calibration in gamma-ray fields. Due to their small size of around 3 x 3 x 1 mm3 and mass of around 20 mg TLDs have been applied for radiation measurements on board various space stations and Space Shuttles since the beginning of the space age. The TLDs providing the basis for measurement of the spatial dose distribution within the MATROSHKA torso were embedded in polyethylene tubes. A total number of 356 TLD tubes was used in the 33 slices of the phantom. All the slices with even numbers were equipped with TLDs from HAMLET partner IFJ-PAN, Krakow, Poland, while the odd-numbered slices were shared by the HAMLET partners TUW, Vienna, Austria, and DLR, Cologne, Germany. In total, this amounts to 784 measurement points for IFJ-PAN, 405 for DLR and 407 for TUW resulting in a total number of 1596 discrete measurement points for the build-up of the three-dimensional dose distribution model of the MATROSHKA experiment. The build-up of the discrete 3D dose distribution using data from passive thermoluminescence detectors for the first three MATROSHKA experimental phases is shown in the following figures: Figure WP1-3: MTR-1 3D (for the MTR-1 experimental phase accomplished outside the ISS); Figure WP1-4: MTR-2A 3D (for the first intravehicular exposure MTR-2A in the Russian Pirs module) and Figure WP1-5: MTR-2B 3D (for the second intravehicular experiment MTR-2B in the Russian Zvezda module). These three figures show in detail how the discrete dose distribution is built up using the data from thermoluminescence detectors supplied by the HAMLET partners DLR, IFJ-PAN and TUW.
(See: Figure WP1-3: MTR-1 3D)
(See: Figure WP1-4: MTR-2A 3D)
(See: Figure WP1-5: MTR-2B 3D)
Figure WP1-6: MTR - All missions 3D shows the comparison of the discrete 3D absorbed dose distribution measured for the three MATROSHKA experimental phases (MTR-1, MTR-2A and MTR-2B) on the basis of more than 4800 thermoluminescence detector measurements for each mission. It is evident that the absorbed dose determined for the extravehicular MTR-1 mission ranged between 0.5 and 0.1 mGy/day, going from the skin to the inner parts of the body, while both the dose range and gradient for the intravehicular exposures were considerably lower (0.23 to 0.13 mGy/day for MTR-2A and 0.21 to 0.14 mGy/day for MTR-2B, respectively). The decrease in absorbed dose at the surface and the upper parts of the body is due to the higher shielding inside the ISS, which reduces primarily the dose delivered by low-energetic protons when crossing the South Atlantic Anomaly. In contrast, the dose at deeper organs - mostly arising from GCR - was nearly constant despite the different exposure conditions in- an outside the space station. The reason for this is found in the high energy of the GCR component and in the self-shielding of the body.
(See: Figure WP1-6: MTR - All missions 3D)
The data generated by the thermoluminescence detectors -located either inside the phantom for the measurement of the discrete 3D absorbed dose distribution map oron the surface of the phantom for the measurement of the skin dose as well as in dedicated organs for the measurement of the organ dose - is further processed in Work Package 4 when building up a continuous dose distribution map for the MATROSHKA experimental phases.
Nuclear Track Detectors: A second type of passive detectors applied within the MATROSHKA experiment were plastic nuclear track detectors (PNTDs) also known as CR-39 detectors. Upon traversal of a heavy charged particle the molecular bonds of the material are broken, thereby producing a latent track. After etching in a caustic solution this nanometre-sized tracks are widened and can be observed under an optical microscope. Based on the calibration of the applied detectors at ground-based accelerator facilities (see also Work Package 2), it is possible to deduce the absorbed dose and the dose equivalent of the heavy ion contribution by measuring dedicated track parameters.
(See also: Figure WP1-7: MTR CR-39)
The data generated by nuclear track detectors - located either on the surface of the phantom for the measurement of the skin dose or in dedicated organs for the measurement of the organ dose - were further combined in Work Package 4 with the data from thermoluminescence detectors in order to calculate the organ doses and, from these values, the effective dose, which is a prerequisite for radiation risk assessment.
Besides the passive radiation detectors also active radiation detectors where used within the MTR-1 and MTR-2B missions, most notably the DOSimetry TELescope (DOSTEL) mounted on top of the head of the MATROSHKA facility.
Active Detectors: The DOSTEL instrument is based on two identical passivated implanted planar silicon (PIPS) detectors produced by Canberra Semiconductors; it was designed to measure the energy deposited by charged particles. One detector has a nominal thickness of 300 µm and the other one a thickness of 150 µm. Both detectors have a sensitive area of 693 mm². They are mounted in a distance of 15 mm, forming a telescope with a geometric factor of 824 mm² sr for particles arriving from the front. The MTR-DOSTEL measures count rates in 100- or 20-second time resolution as well as energy deposition spectra, which are integrated over 45 minutes. In case of high count rates, for example during crossings of the South Atlantic Anomaly (SAA), the instrument switched to SAA mode and records an additional energy deposition spectrum. The integration period of these SAA energy deposition spectra depended on the time duration of high count rates.
The energy deposition spectra measured mode was used to calculate the mean quality factor. This factor describes the biological effectiveness of radiation. With this information and the knowledge of the total absorbed dose in the detectors it is possible to derive the dose equivalent (which serves as substitute for effective dose).
As an example of the results generated with the DOSTEL Figure WP1-8: DOSTEL-1 shows the DOSTEL count rates measured in the silicon detector for a two-day time interval in May 2004. This count rate plot can further be evaluated by the correlation of the count rate with the ISS orbit, resulting in a 2D count rate plot versus longitude and latitude as given in Figure WP1-9: DOSTEL-2. This count rate plot over the orbit of the space station highlights the passage for different time periods as well as the change in radiation environment conditions over time and orbit of the space station and clearly shows the increase in count rate with increasing longitude and the high count rates due to the low-energetic protons while crossing the South Atlantic Anomaly over the coast of Brazil.
A summary of the absorbed dose and dose equivalent values determined with the DOSTEL instrument for the MTR-1 mission outside the ISS is given in
Table WP1-1: DOSTEL-MTR-1, while the results for the inside exposure during the MTR-2B mission are given in Table WP1-2: DOSTEL-MTR-2B. The results clearly indicate the high difference in dose equivalent due to the crossing of the South Atlantic Anomaly (367 µSv/day for the MTR-1 mission in comparison to 72 µSv/day for the
MTR-2B inside mission) and the quite similar contribution from GCR (245 µSv/day for the MTR-1 mission in comparison to 310 µSv/day for the MTR-2B mission).
(See also: Figure WP1-8: DOSTEL-1)
(See also: Figure WP1-9: DOSTEL-2)
(See also: Table WP1-1: DOSTEL-MTR-1)
(See also: Table WP1-2: DOSTEL-MTR-2B)
Since the results - especially for the passive radiation detectors within the MATROSHKA missions - are comprised of data generated by various research groups from all over the world, with 95% of the detectors provided by the HAMLET partners, the essential prerequisite for the combination and comparison of these results was that the relevant detector properties for the applied detector systems were known sufficiently well. This information has been gathered within Work Package 2 of the HAMLET project.
WP2: Detector Characterization:
The aim of Work Package 2 was to characterize the detector systems applied within the MATROSHKA experiment, in terms of their detection properties. The detector characterization was needed in two respects. The first concerned the peculiarity of the conditions encountered by detectors within the MATROSHKA experiment, that is, the complexity of the radiation field and a very long time of exposure. The second requirement for detector characterization came from the great variety of radiation detectors that have been used within the MATROSHKA experiment. Each of the investigators also applied their own measurement and calibration protocols. It was therefore essential to compare performance of detectors and evaluation procedures applied by individual participants to have full understanding of the detector properties and to use this information for the combination of data as performed in Work Package 1.
The main effort of Work Package 2 activities was in the characterization of radiation detectors in ground-based radiation fields available from high-energy particle accelerators, which may be considered as a simulation of sub-sets of the space radiation environment. The HAMLET consortium was granted with two research projects by the National Institute of Radiological Sciences (NIRS), Chiba, Japan and the ESA European Space Research and Technology Centre (ESTEC), Nordwiijk, The Netherlands, for using machine times at the Heavy Ion Medical Accelerator (HIMAC) at NIRS in Chiba, Japan, and the Heavy-Ion Synchrotron (SIS) of the GSI Helmholtz Centre for Heavy-Ion Research in Darmstadt, Germany, as shown in Figure WP2-1: HIMAC-GSI. Within the realized five irradiation campaigns at the HIMAC and two at the GSI, the detectors were exposed to the monoenergetic beams of fully ionized helium, carbon, silicon, neon, argon, iron and nickel nuclei with energies up to 1000 MeV/u.
(See also: Figure WP2-1: HIMAC-GSI)
Due to an international cooperation of DLR with NASA it was further possible to irradiate detectors with protons of energies up to 450 MeV in order to simulate a solar particle event in the NASA Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory (BNL), Upton, NY, USA, as shown in Figure WP2-2: NSRL.
(See also: Figure WP2-2: NSRL)
One focus of the accelerator experiments was the comparison of the response of thermoluminescence detectors (TLD) applied by the HAMLET partners TUW, Vienna, Austria, DLR, Cologne, Germany and IFJ-PAN, Krakow, Poland, within the MATROSHKA experiment. TLDs are solid-state passive dosimeters, their principle of operation being the emission of light upon heating following the previous absorption of radiation energy. The amount of emitted light is a measure of the absorbed dose. The relative radiation detection efficiency of a particular TLD phosphor depends on the ionization density, so it is different for densely ionizing particles and for sparsely ionizing gamma-rays, which are commonly used for calibration. While the occurence of these effects was in principle known, the existing knowledge on this subject was mostly general and qualitative. Analysis of the MATROSHKA data required systematic quantitative investigations of the dependence of thermoluminescence efficiency on radiation type and ionization density, for actual detector types, which were used in space. Some of the obtained results are illustrated in Figure WP2-2: TLD -1 and
Figure WP2-2: TLD -2. The main conclusion from these results is that there is a very good agreement between the different laboratories, in spite of differences of detectors origin and evaluation methods. It also very important, that for all investigated types of detectors, the dependence of the termoluminescence efficiency on LET for high-energy ions may be described by a unique empirical function. This is a remarkable finding, as in general (i.e. considering the full energy range), the dependence of efficiency on LET splits into many branches, corresponding with different ion charges. Thus, in case of cosmic radiation, which is dominated by high-energy ions, it was possible to use functions correcting TL efficiency.
(See also: Figure WP2-2: TLD -1)
(See also: Figure WP2-2: TLD -2)
Another type of the studied detectors were the nuclear track etch detectors (NTD). They permit to determine the radiation dose above a given threshold value of ionization density, parameterized by LET (linear energy transfer), depending on type of the detector material and the evaluation method. To visualize the latent tracks induced in the detector sheets by the different ionizing particles a chemical etching procedure is applied. The detectors are evaluated after etching by an image analyser system, which recognizes the tracks and measures their geometrical and optical parameters, which allow obtaining the track etch rate ratio (V) for each particle. V is converted into LET using the appropriate calibration functions and then the dose can be calculated from the LET spectra. A calibration function can be determined by exposing detectors with particles of known charge Z, mass M, energy E and LET. Determining of such calibration curves was one of the goals of the WP2 investigations. An example of a calibration curve is given in the Figure WP2-4: CR-39. The HIMAC investigations enabled also evaluation of the angular dependence of NTD efficiency.
(See also: Figure WP2-4: CR-39)
The third type of detectors studied with the high-energy ion beams were "Silicon-Scintillator Devices" (SSD) operated by HAMLET partner CAU, Kiel, Germany which have been positioned inside various organs within the MATROSHKA experiment. The SSD detectors consists of an organic scintillator fully covered by semiconductor photo diodes. The scintillator is used to measure charged particles as well as neutrals. To distinguish charged and neutral particles the photo diodes are used since they are also detecting charged particles directly.
(See also: Figure WP2-5: SSD)
Besides the calibration and efficiency studies, in frame of the irradiation campaigns at the accelerator centres, also exposures of the head of the MTR phantom were realized. In this way, the dose distributions inside the head were measured for various ions, as given in
Figure WP2-6: HIMAC - Depth Dose, which were further used for serve as benchmark of the computer transport codes in Work Package 4.
(See also: Figure WP2-1: HIMAC-GSI)
(See also: Figure WP2-6: HIMAC - Depth Dose)
Another study realized within the Work Package 2 was devoted to the investigation of long term stability of the performance of thermoluminescence detectors - taking into account the very long duration of the various MATROSHKA phases. This study was accomplished at IFJ, Krakow, Poland and consisted of the over one-year storage of various types TLDs, with irradiations realized at different times during the storage period. Two storage temperatures (room temperature and -18°C) and two radiation modalities (gamma-rays and thermal neutrons) were used. Results showed that there are no significant instabilities of TLD signals.
For a precise comparison of measured data it is necessary to prove, that also the calibration performed by the various research groups is consistent. For this an intercomparison experiment was realized, in which TLDs from DLR, TUW and IFJ were exposed to gamma calibration doses in each of the three participating laboratories. The results of this experiment show that agreement between calibration factors used by different groups is better than 3%.
(See also: Figure WP2-6: TLD - Properties).
Work Package 2 and the relevant results gathered within this Work Package proofed, that the combination of the measured data from the different groups from the MATROSHKA space experiments can be pooled together to construct a 3 D dose model.
WP3: ISS Space Data Intercomparison
In view of exploiting the maximum possible information regarding projection of acute and late radiation risks for space travellers on current and future missions of exploration, it did not seem appropriate to treat MATROSHKA as a stand-alone investigation, but rather put its outcome into the context of other radiation measurements conducted in timely parallel. For that to be done deserved particular attention to be paid to the instrument responses and detection principles in order to facilitate cross-comparison and harmonization of the measured data.
On the HAMLET website, a reference database has been set up and updated frequently to enable public access of all articles published in topical journals of the Science Citation Index or presented at international conferences that are related to space-borne phantom experiments and radiation measurements on board the ISS since launch of its first components in 1998 (Figure WP3-1: HAMLET-Database-Literature). The papers are linked to by categories and the ISO-standardized Digital Object Identifier system. As with 30 September 2011, the subcategories contained the following number of references grouped by instrument:
* Active radiation monitoring: 81 articles (including supplementary publications)
* Passive radiation monitoring: 79 articles (including supplementary publications)
* Phantom experiments: 42 articles (including supplementary publications)
(See: Figure WP3-1: HAMLET-Database-Literature)
The subsection "Active radiation monitoring" addresses instrumentation used for area dosimetry and science-driven experiments, which is based on silicon detector and ionization chamber principles, such as
* ALTEA detector suite
* Bonner Ball Neutron Detector
* Charged-Particle Directional Spectrometer
* DB-8 silicon detector
* Dosimetry Telescope
* Liulin Mobile Dosimetry Unit
* R-16 ionization chamber
* Sileye-3/Alteino silicon strip telescope
* Tissue-Equivalent Proportional Counter
* TriTel silicon telescope
The entries under the subsection "Passive radiation monitoring" comprise references to measurements applying to area and personal dosimetry as well as science-driven investigations as:
* Nuclear and superheated emulsions
* Thermally and optically stimulated luminescence dosimeters
* Nuclear track detectors
* Combinations of the above methods
Under the category "Phantom experiments" publications related to various phantoms experiments as:
* Phantom head and torso "Fred" flown by NASA on the Space Shuttle and the ISS
* Russian spherical phantom experiment on board the Mir orbital station
* Polyurethane-based spherical phantom MATROSHKA-R installed in the Russian Segment of the ISS
have been listed. A selection of review and supplementary papers in each category should support understanding of the detector principles and calibration as well as interpretation of experimental results.
As it turned out, only those investigations related to area monitoring or science-driven experiments were of relevance to MATROSHKA, which had been conducted in the same segment of the ISS, be it either the Zvezda Service Module or the less shielded Pirs Module.
(See: Table WP3-1: Space Experiments)
For all other studies, in particular measurements outside the station, the very different shielding configurations did not allow for meaningful cross-comparison. The dose rates measured at the surface of the MATROSHKA facility during MTR-2A in Pirs and MTR-2B in Zvezda, respectively, proved to be in overall agreement with data evaluated from Pille-MKS thermoluminescence dosimeter measurements, which are the backbone of area monitoring on board the Russian Segment of the ISS (Figure WP3-2: PILLE -Results). Dose distributions determined in the MATROSHKA-R spherical phantom showed a high level of both qualitative and (particularly for the heavier shielded Service Module) quantitative consistency with the skin and depth dose profile measured in the anthropomorphic MATROSHKA mannequin (Figure WP3-3: MTR-Skin dose).
(See: Figure WP3-2: PILLE -Results)
(See: Figure WP3-3: MTR-Skin dose)
WP4: Experimental and Calculated 3D Radiation Model
For this work package two computer tomography (CT) scans of the MATROSHKA phantom were first performed. The data from the CT scans were then used to build a Voxel model called NUNDO (Numerical RANDO) of the phantom. Figure WP4-1: CT-Model shows the real MATROSHKA phantom and the CT scans of it, the Voxel phantom NUNDO. The material density of the skeleton is equal to 1.3 g/cm3.
(See: Figure WP4-1: CT-Model)
After that a computer program, OrDoCal (Organ Dose Calculation), was developed for the interpolation of the discrete 3D point dose measurements over the whole phantom volume and for calculation of the organ doses based on the data input from Work Package 1. Using this software, the data obtained within the three MATROSHKA experiment phases experiment were analyzed and a 3D dose distribution based on the measurements within the phantom was calculated. The relevant continuous 3D dose distributions are given in Figure WP4-2: MTR-1 3D for the MATROSHA-1 exposure outside the ISS; in Figure WP4-3: MTR-2A 3D for the 1st inside exposure in the PIRS module and in Figure WP4-4: MTR-2B 3D for the 2nd inside exposure in the Zvzeda module.
(See: Figure WP4-2: MTR-1 3D)
(See: Figure WP4-3: MTR-2A 3D)
(See: Figure WP4-4: MTR-2B 3D)
Clearly seen in the comparison of the three figures is the high dose gradient for the MTR-1 outside exposure from the skin to the inner organs due to the high contribution of electrons and protons from the South Atlantic Anomaly. Due to shielding of the International Space Station this contribution is reduced and the gradient is way flatter for the inside exposures. Based on the development of the NUNDO phantom it is now possible to include the organs inside the continuous 3D dose distribution and calculate the relevant organ absorbed doses as given in Figure WP4-5: MTR Organ Absorbed Dose for the three MATROSHKA missions. Adding the data from the nuclear track etch detectors one can further calculate the organ dose equivalents as given in Figure WP4-6: MTR Organ Dose Equivalent. With this information the effective dose for the three MATROSHKA mission could be calculated and is given in Figure WP4-7: MTR Effective Dose.
(See: Figure WP4-5: MTR Organ Absorbed Dose)
(See: Figure WP4-6: MTR Organ Dose Equivalent)
(See: Figure WP4-7: MTR Effective Dose)
The results for the effective dose, which is pre-requisite for the calculation of the radiation risk for long duration space missions, indicate an effective dose of 0.69 mSv/day for the outside exposure and a variation of the effective dose from 0.53 to 0.57 mSv/day for the exposures inside the Russian part of the International Space Station.
The radiation transport calculations for the MTR experiments were performed using the 3D multi-purpose particle and heavy ion Monte Carlo transport code PHITS coupled to the constructed Voxel Phantom NUNDO. The external space radiation environment was calculated with models from the CREME96 and SPENVIS model packages. For the MTR-1 simulations, the phantom, together with the container, was placed on the aluminium foundation of 1 g/cm2 thickness and the inside of the foundation as well as the inside of the container were filled with 1 atm. air. The container was made of 0.35 g/cm2 of carbon fibre composed by hydrogen (4.2%), carbon (42.2%), oxygen (4.2%), nitrogen (28.5) fluorine (8.4) silicon (11.7) chlorine (0.6) and sulphur (0.3). The container together with the foundation, were located on the simplified ISS geometry, chosen as an aluminium cylinder shape with a thickness of 15 g/cm2, as shown in Figure WP4-8: MTR-1 Simulation Set up.
(See: Figure WP4-8: MTR-1 Simulation Set up)
Everything was placed in a spherical radiation source where the particles were emitted inward and isotropically. Heavy ions with atomic numbers up to 28 and energies up to 100 GeV/n were considered in the GCR, and GCR fluxes were from year 2004, where the apogee 365 km, perigee 345 km and inclination 52o approximated the ISS flight path. During the MTR experimental period, February 2004 to October 2005, the solar activity gradually decreased from solar maximum to solar minimum, so the TP component of the cosmic radiation described by the AP-8 model for minimum solar activity was here adopted.
The phantom and results of simulations of the measurements performed with TLDs in tubes 3B, 4B and 5A located in the head region (marked with a red rectangle) of the phantom is shown in Figure WP4-9: Simulation Results 1. Both, the simulated and experimental data are given as doses in water, with TL efficiency corrections. Simulations were performed separately for Trapped Protons (TP) and Galactic Cosmic Radiation (GCR), and the total dose is given as the sum of the TP and GCR contributions. The comparison for all the measured 3D dose data with the simulated data is given in Figure WP4-9: Simulation Results 2.
(See: Figure WP4-9: Simulation Results 1)
(See: Figure WP4-9: Simulation Results 2)
The absorbed dose in each organ of the phantom NUNDO was defined as the total energy deposited in the organ divided by the mass of this organ. The dose equivalent was calculated with calculated according to the Report 60 of the International Commission on Radiological Protection. Simulations of the organ doses and the dose equivalents were done separately for TP, GCR and Trapped Electrons (TE). The calculated organ dose and dose equivalent rates for MTR-1 experiment are summarized and compared to the corresponding experimental data in Figure WP4-10: Organ Dose and Table WP4-1: Organ Dose. The simulated results are both shown as the sum of all radiation components contributed to the total dose (GCR, TP and TE), and when the TE component is subtracted, to clearly show the significance of TE on the most outer tissue doses. The TE contributions are negligibly small to the doses deep inside the human body, since the energies of the trapped electrons are so low that they generally stop very close to the surface of the body. When comparing the simulated data with the MTR experimental results, the agreement is good for the inner structures but rather large discrepancies are observed for the most outer organs, like skin or breast due to an underestimation of the container thickness. The disagreement of the calculated outer organ doses with the experimental values suggested that the container thickness of in our simulations was too thin compared to the experimental setup, where additional NOMEX® poncho and multilayer insulation covered the phantom. To check how the container thickness influences the results, additional simulations with the same geometry but with a thicker container were performed. These simulations gave better agreement between the simulated and measured dose for the outer organs, e.g. the skin.
(See: Figure WP4-10: Organ Dose)
(See: Table WP4-1: Organ Dose)
Simulations of the MTR-2B experiment, inside the ISS, were also performed. In
Figure WP4-11: MTR-2B Simulation Set up, the geometry of the phantom, container and foundation (a), and the simplified geometry of the ISS module with the phantom (b), is shown. However due to large uncertainties in the shielding (wall thicknesses, experimental racks, etc.), the simulated doses underestimated the measured ones as given in
Figure WP4-11: Organ Dose MTR-2B.
(See: Figure WP4-11: MTR-2B Simulation Set up)
(See: Figure WP4-11: Organ Dose MTR-2B)
To summarize WP4, simulations of the MTR-1 and MTR-2B were performed with the PHITS code, and the organ dose and the dose equivalent rates were calculated. Comparison to the experimental data taken during the MTR-1 experiment, simulating an EVA, showed a good agreement for the inner organs, considering all the approximations, uncertainties in the geometry of the ISS, and the measured data. The simulated doses in the outer organs had a larger disagreement with the measured values, than for the inner organs due to a strong dependence of the thickness of the container to the dose levels in these outer structures. Since measurements were performed with passive detectors over a long time period, there were changes of local shielding inside the ISS, altitude and phase in the solar cycle during the measurements. As the MTR-1 experiment was performed during a long time period, 1.5 year, it is most probably not enough to only adopt the fluxes from 2004, as done in this study. It would have been more correct to make averages of the energy spectra of GCR and TP at solar minimum and maximum conditions. The performed study showed that the best agreement between the simulated and measured doses was obtained for a container thickness of above 0.35 g/cm2 but below 0.7 g/cm2. This study also showed that the contribution from the TP component to the total dose and the dose equivalent decreases with the depth in a phantom, when outside the ISS, and when calculating the mean values for the solar minimum and the solar maximum activities. The GCR dose and the dose equivalent values increase 20% when the mean dose values for the solar minimum and the solar maximum are calculated comparing to the dose values calculated from the spectra from 2004. A higher altitude does not significantly change the dose contribution from the GCR during an EVA.
The simulations performed for MTR-2B, simulating an IntraVehicular Activity (IVA), deviated more from the measured values than for MTR-1, most likely due to the oversimplified geometry used in these simulations.
In addition to the simulations of the MTR phantom in space with PHITS, simulations of irradiations of the head of MTR phantom performed at the HIMAC accelerator in Chiba, Japan, was performed with the 3D multipurpose particle and heavy ion transport package GEANT4 resulting in very good agreement between the measured and calculated results. These results confirm the importance to know the local shielding configuration in detail when performing simulations of experiments on board the ISS.
WP5: Dissemination of Results:
The overall goal of Work Package 5 was the dissemination of the results of the HAMLET project to the scientific community as well as the public audience.
The presentation of scientific data to the public audience was strongly emphasized within the HAMLET project. Raising the public awareness and educating the audience, especially in the well-debated field of radiation, was taken as an essential task. The HAMLET project gives us a perfect 'tool' by connecting the issues of 'space radiation' and 'radiation on manned flights to Moon and to Mars' with the human 'subjects', especially considering that MTR simulates a human in the space radiation environment.
The Public Outreach of HAMLET was optimized by installation of the HAMLET web page under http://www.fp7-hamlet.eu. The scope of this page is not only to inform the public about the project itself, but rather provide a comprehensive but concise overview of the space radiation environment, detector instrumentation, radiation transport models and associated topics, and highlight the expertise of the participating institutions. An image gallery serves as an online repository of digital images pertaining to the MATROSHKA experiment and HAMLET activities.
Five dedicated Public Outreach Events, hosted and organized at the bases of the participating institutions, further increased the awareness of the public audience to the significance of radiation exposure for the future development of human spaceflight.
http://www.fp7-hamlet.eu/index.php/public-outreach-days/general-information
The science achievements of the HAMLET project are disseminated publicly through a web database. Following the definition of a unified structure for the experimental data provided by the individual participants, a front end of the web database has been designed which allows for convenient and reliable uploading of the processed dosimetric data under
http://www.fp7-hamlet.eu/index.php/database. The data archive currently contains absorbed dose rates measured under extravehicular activity (EVA) conditions during the MTR-1 experiment by miniature luminescence detectors at about 4,800 sites within the anthropomorphic phantom body. The user is graphically assisted in navigating through the torso. The data archive will be expanded in the future with data from the MTR-2A and MTR-2B experiment phases, as well as with the data from the active radiation detectors upon publication of these results in scientific journals.
(See: Figure WP5-1: HAMLET-Science-Database)
(See: Figure WP5-2: HAMLET-Science-Database II)
Besides the presentation of the data generated within the HAMLET project on the HAMLET webpage in the frame of the web database big emphasises was laid on the presentation of scientific data related to the four HAMLET Work Packages at numerous conferences, workshops and seminars over the lifetime of the HAMLET project. The outcome was further presented in peer reviewed publications.
Potential Impact:
Introduction
The main purpose of science is the increase of knowledge to help mankind. Knowledge, based on international joined experiments in space, can only be increased by the close cooperation of the participating investigators. If this cooperation is not strongly emphasized, the community will miss vast amounts of collected experimental data which will be lost for science, and therefore for the advancement of knowledge. The goal of the HAMLET project as described in the HAMLET Mission Statement implements in detail these thoughts.
"The aim of HAMLET is the effective scientific exploitation of data obtained from the ESA MATROSHKA project. This will be achieved by bringing together leading European scientists in the field of space dosimetry to increase and enhance the output of the project and present it to the European scientific community as well as the public audience."(HAMLET MISSION STATEMENT)
Scientific endeavours like the MATROSHKA project are only possible with strong international cooperation. HAMLET includes seven European research institutes all of whom participate in the MATROSHKA project. MATROSHKA is the largest international research initiative ever performed in the field of space dosimetry and combines the expertise of leading research institutions around the world. It consequently generates an extensive pool of data of exceptional value to the scientific community. This potential can only be fully utilized by close cooperation and extensive joint research actions of the investigating groups. Individually, all groups produced valuable scientific data sets, but only the strong cooperation and close integration of multiple, highly skilled scientific groups, leads to the acquisition of new and important knowledge about the effects of space radiation on the human body. The goal of HAMLET was therefore not the local or national organization of expert scientists, but the building of cooperation on a European scale, to utilize the collected data to greatly advance the field of space dosimetry. The long-term MATROSHKA experiment is an exceptional chance for scientific advancement in the field of space dosimetry, and as such, the scientific community shall aim to extract the maximum information from its output. European
"Current space exploration programmes, in Europe and elsewhere, intend to extend the human presence, in a real or virtual way, through missions to the Moon and to Mars or through automatic missions in direction to objects of the solar system." (European Commission- FP7 Call)
The exploration of space as seen in specific projects from ESA within the Aurora Programme, for example, the search for life on MARS (EXOMARS) or other initiatives such as the further exploration of the Moon, act as groundwork for human long duration space missions. However, one of the main constraints for long duration human missions in space, besides the psychological factors and the impact of microgravity on the human physiological system, is radiation. The radiation load on astronauts and cosmonauts in space (as for the ISS) is a factor of 100 higher than on earth. This radiation load will further increase should humans travel to MARS. In preparation for long duration space missions it is important to ensure that ESA has an excellent capability to evaluate the impact of space radiation in order to secure the safety of the astronaut/cosmonaut and minimize their risks. It is therefore essential to gather and focus all possible knowledge in terms of space radiation experiments to enable future generations to travel where nobody has gone before.
Dissemination & Exploitation of Results
The dissemination of the research results is one of the key concerns of the HAMLET project. As a general rule, all the knowledge gained through realization of the HAMLET project is open and available to the scientific community and public alike. A strong intention of the project consortium was the public availability of not only the summary of the main results, as is usual in scientific articles and reports, but to also provide the basic data sets to all interested groups and persons. We believed that the data produced in this project, including in particular, experimental and calculated 3D dose distributions inside the phantom, are potentially of great value for space radiation scientists world-wide. Therefore, the free and convenient access to numerical, tabulated results of HAMLET is one of the main responsibilities of this project.
HAMLET WEBPAGE
Apart from the scientists the other important audience is the general public. The presentation of scientific data to the public is strongly emphasized within the project. The Public Outreach of HAMLET was optimized by installation of the HAMLET web page under
http://www.fp7-hamlet.eu with the following content:
* Introduction to the HAMLET project - including updates of project schedule
* The space radiation environment
* Human presence in space and the risks due to radiation
* Space radiation measurements
* Phantom experiments in space
* MATROSHKA Experiment - Timeline, Documentation
* MATROSHKA Experiment - Scientific Data
* MATROSHKA Experiment - 3 D Dose Distribution Model
* Literature database
* Download Section
* Public Outreach Section
The scope of this page is not only to inform the public about the project itself, but rather provide a comprehensive but concise overview of the space radiation environment, detector instrumentation, radiation transport models and associated topics, and highlight the expertise of the participating institutions. An image gallery serves as an online repository of digital images pertaining to the MATROSHKA experiment and HAMLET activities.
(See: Figure MAIN-1: HAMLET Webpage)
HAMLET Public Outreach Events
The HAMLET consortium held five dedicated HAMLET Public Outreach (PO) Events within the timeframe of the HAMLET project, hosted and organized at the bases of the participating institutions, to further increase the awareness of the public audience to the significance of radiation exposure for the future development of human spaceflight.
The intention of these 'Public Outreach Events' was the presentation of the 'science background', the 'current state of research' and the 'further planned activities' of the group to a scientific interested public audience as also given in the overall topics:
* Human Space Exploration
* Hazards from Space Radiation
* How Do We Measure Space Radiation?
* The Matroshka Project
* From Apollo to the ISS
* To Moon, Mars and Beyond ...
The HAMLET project partners gave talks about the baselines of radiation protection in space, the risks of long-duration space flight to humans, the scientific reason behind the MATROSHKA experiment, and the current status of the HAMLET project. This was accompanied with 'hands-on experience' for the general public to space radiation hardware, e.g. a training model of the MATROSHKA phantom.
The 1st HAMLET Public Outreach (PO) Event was held on 1-2 April 2009 at Vienna University of Technology, Vienna, Austria. The keynote lecture on radiation risk in human spaceflight was given by Prof. em. Dr. Jürgen Kiefer, from 1970 to 2002 Professor of Biophysics at Justus Liebig University Giessen, Germany. The event was acknowledged also by the Vienna City Council for Cultural Affairs and Science Policies and included a space:?rt Exhibition that attracted considerable audience. The 2nd HAMLET PO Event was held on 21 January 2010 at St. Catherine's College in Oxford, organized by HAMLET partner HPA followed by the 3rd HAMLET Public Outreach at the 12 October 2010 organized by HAMLET partner AERI at the Budapest University of Technology, Hungary. The 4th Public Outreach Event organized by HAMLET project partner IFJ was held on the 05th April 2011 at the Polish Academy of Arts and Science, Krakow, Poland. HAMLET partner DLR organized the 5th HAMLET Public Outreach event at the 15. September 2011 at the Bonn-Rhine-Sieg University of Applied Sciences, Campus Rheinbach in Rheinbach, Germany in the frame of the Annual Meeting of the German Radiation Research Society. The events attracted attendees with scientific and academic background but also students and an interested public audience. The HAMLET PO Events were advertised trough press releases, magazine articles, leaflets and posters. In addition TV and radio interviews documented the public interest.
(See: Figure MAIN-2: PO-1 Vienna)
(See: Figure MAIN-3: PO-2 Oxford)
(See: Figure MAIN-4: PO-3 Budapest)
(See: Figure MAIN-5: PO-4 Krakow)
(See: Figure MAIN-6: PO-5 Rheinbach)
HAMLET Science achievements
The science achievements of the HAMLET project are disseminated publicly through a web database. Following the definition of a unified structure for the experimental data provided by the individual participants, a front end of the web database has been designed which allows for convenient and reliable uploading of the processed dosimetric data under
http://www.fp7-hamlet.eu/index.php/database. The data archive currently contains absorbed dose rates measured under extravehicular activity (EVA) conditions during the MTR-1 experiment by miniature luminescence detectors at about 4,800 sites within the anthropomorphic phantom body. The user is graphically assisted in navigating through the torso. The data archive will be expanded in the future with data from the MTR-2A and MTR-2B experiment phases, as well as with the data from the active radiation detectors upon publication of these results in scientific journals.
HAMLET Exploitation of results
Besides the web-based activities, the participants aimed for publishing in high rated scientific journals - and presenting summaries of the output of their work to the scientific community at relevant international conferences and workshops. As an example the presentations were aimed for interdisciplinary international conferences as the biannual Committee on Space Research (COSPAR), the annual International Astronautical Federation (IAF), as well as for meetings directly related to space radiation research, as the annual International Workshop for Space Radiation Monitoring (WRMISS) http://www.wrmiss.org organized by Guenther Reitz (DLR). Presentations at the mentioned meetings increased the public awareness as well as initiate discussions within the scientific community.
Dissemination Plan after HAMLET
The dissemination of results gathered within the HAMLET project will not stop after the end of HAMLET. The intention of the project partners is the following:
HAMLET Webpage: The HAMLET webpage will be kept online under http://www.fp7-hamlet.eu for the upcoming years with updates related to the MATROSHKA project and the work still performed by the project partners. This update of the webpage will also include the update of the Literature database which was set up in the frame of Work Package 3 of HAMLET.
HAMLET Database: The database for the science data generated within HAMLET - both for the passive radiation detectors, as well as for the active radiation detectors - will be kept online as part of the HAMLET webpage and populated upon final publication of the scientific data gathered within the HAMLET project by the project partners.
HAMLET Publications and Presentations: A vast amount of data has been analysed and compared and put into perspective within the three years of the project lifetime. This data was not only limited to the data evaluation performed for the MATROSHKA space experiments, but also focused on the ground based intercalibration of radiation detector purposes and submitted as part of the deliverables and milestones of the HAMLET project. The main aim of the HAMLET project partners for the upcoming time to come will be the final presentation and publication in peer reviewed journals of the outcome of the HAMLET project.
Impact
The HAMLET consortium aimed to advance the current knowledge by focussing and connecting the leading European scientists in space radiation dosimetry, to explore and exploit the vast amount of data gathered within the European MATROSHKA project, thereby:
* Developing tools to archive, access and process data obtained from different sources
* Mobilising the best expertise for the analysis and interpretation of space data, selecting the most innovative and challenging objectives in emerging scientific fields
* Promoting the contribution of space assets to the scientific and technological knowledge and foster its transfer to educational bodies
The development of tools to archive and analyse raw and processed data was one of the main goals of the HAMLET project. By providing the investigators with a common tool, in the form of a web-based infrastructure, they were able to upload their individual data sets, and bring these data sets in alignment with data sets from the other participants, therefore enabling the integration and full exploitation of the data.
The HAMLET consortium brought together the leading European scientists in space dosimetry, for radiation monitoring using both active and passive detectors, for theoretical calculations of the radiation environment in space, and for the assessment of doses to personnel inside and outside of space vehicles. This comprehensive expertise in the different methods of radiation detection and calculation lead to a unique data set now available to the scientific community.
After the accomplishment of the work, Europe has now acquired an added exceptional scientific value, which up to now, did not exist world-wide. This knowledge will not only be disseminated in the scientific community, but will also kept as an open source and brought to the public audience. A result of the the HAMLET project already fostered the cooperation with GSI, Darmstadt, Germany and NIRS, Chiba, Japan in the field of radiation protection and cancer research.
DLR provided GSI, Darmstadt, Germany an MATROSHKA phantom for the usage as „patient" in the frame of the FP7 ALLEGRO project aiming for the determination of the out of field radiation doses received during cancer treatment and the comparison of different treatment modalities (IMRT, Proton and Carbon beams). DLR provided radiation detectors and its expertise for their evaluation within this project.
Irradiations have been performed at:
* Klinikum Goethe University (KGU) in Frankfurt, Germany, IMRT (Intensity Modulated Radiation Therapy) photons;
* Svedberg Laboratory (TSL) in Uppsala,Sweden, (Passively modulated protons)
* Paul Scherrer Institute (PSI) in Villigen, Switzerland (Scanned protons)
* National Institute of Radiological Sciences NIRS (HIMAC), Chiba, Japan, (Passively modulated carbon ions)
* Helmholtzzentrum für Schwerionenforschung GmbH (GSI) in Darmstadt, Germany, (Scanned carbon ions)
The outcome of this cooperation was submitted in two papers to the Journal „Radiotherapy and Oncology" at the end of September 2011.
Further on the results of the HAMLET project are considered as input by the International Commission on Radiological Protection (ICRP) Task Group 67 "Radiological Protection in Space" for the description of radiation fields and doses inside the human body as part of its report titled "Assessment of Radiation Exposure of Astronauts in Space". This will constitute the first international regulation in how to assess the radiation exposure of Astronauts. A further step will be, based on this ICRP report, a new international report on risk assessment of space radiation.
List of Websites:
http://www.fp7-hamlet.eu
http://www.fp7-hamlet.de
http://www.fp7-hamlet.at
http://www.fp7-hamlet.se
http://www.fp7-hamlet.hu
http://www.fp7-hamlet.org.uk
To quote Seneca's Megara, Hercules' wife, saying: "Non est ad astra mollis e terra via" - the road for humans to travel to the stars is posing manifold challenges. Among all obstacles one has to solve to work and live in space, such as adverse physiological effects of microgravity and psychosocial concerns related to the stresses of confined isolation and interpersonal dynamics, the probably biggest threat to human health is posed by cosmic rays, especially when thinking of long-term missions of exploration. The radiation load on space travellers in low-Earth orbit, like on the International Space Station (ISS), is a factor of ~100 higher than the natural radiation exposure on ground, and it will further increase should humans return to the Moon or travel to Mars in the future. The risks associated with exposure to space radiation have to be determined as accurately as possible in order to support safe human exploration of the solar system. One way to quantify these risks is by measuring the radiation doses to vital organs of the human body inside human-like phantoms, as performed through the ESA facility MATROSHKA (MTR) on board the ISS. MATROSHKA houses an anthropomorphic phantom torso and is operated under the scientific project lead of the German Aerospace Center (DLR). The experiment is dedicated to determining the radiation exposure of astronauts when staying inside or outside the space station. The phantom is equipped with more than 6,000 radiation detectors to measure the depth dose and organ dose distribution in the body. It is the largest international research initiative ever performed in the field of radiological protection in space and combines the expertise of leading scientific institutions around the world, thereby generating a huge pool of data of potentially immense value for research. MATROSHKA was launched to the ISS in January 2004. Up to March 2011, four missions have been accomplished. During the MTR-1 experimental phase (2004-2005) the facility was installed outside the Russian Service Module (Zvezda) simulating a long-duration astronaut space walk. The MTR-2A experimental phase was carried out in the year 2006 inside the Russian docking compartment (Pirs). The third phase (MTR-2B) in the years 2007 to 2009 saw the phantom mounted inside Zvezda, followed by a fourth exposure inside the Japanese Experiment Module from 2010 to 2011 (MTR-2 Kibo). The FP7 project HAMLET (Human Model MATROSHKA for Radiation Exposure Determination of Astronauts, http://www.fp7-hamlet.eu aimed at the effective scientific exploitation of data obtained from the ESA MATROSHKA experiment. This was achieved by bringing together leading European scientists in the field of space dosimetry to increase and enhance the output of the project and present it to the European scientific community as well as the public audience. The HAMLET project focused on the detailed analysis, compilation and comparison of the data generated by the MATROSHKA experiment for the development of a three-dimensional model of the dose distribution inside a human body, both simulating an astronaut's space walk and an astronaut working at different locations inside a space station. The developed model has been verified and benchmarked using complex Monte Carlo radiation transport codes. Further, an extensive ground-based programme has been initiated at diverse heavy-ion accelerator facilities around the world to determine the response and characteristics of the radiation detectors used within the MATROSHKA project. These data serve as benchmark against radiation transport codes and further supported verification of the accuracy of the developed dose-distribution model. The outcome of the work performed within HAMLET enabled the determination of the effective dose in and outside the space station, contributed to improved radiation risk assessment for long-duration spaceflight and greatly helped securing the future safe presence of humans in low-Earth orbit and beyond.
Project Context and Objectives:
HAMLET - Mission Statement
The aim of HAMLET (http://www.fp7-hamlet.eu) is the effective scientific exploitation of data obtained from the ESA MATROSHKA project. This will be achieved by bringing together leading European scientists in the field of space dosimetry to increase and enhance the output of the project and present it to the European scientific community as well as the public audience.
(See: Figure Summary-0: FP7 HAMLET LOGO)
HAMLET - Context
The radiation exposure in space is a limiting factor, especially when thinking of long-term human presence in space. The radiation load on space travellers in low-Earth orbit, like on the International Space Station (ISS), is a factor of ~100 higher than the natural radiation exposure on ground, and it will further increase should humans return to the Moon or travel to Mars. The health risks associated with exposure to cosmic radiation have to be determined as accurately as possible in order to support safe human exploration of space. One way to quantify these risks is by measuring the radiation doses to vital organs of the human body inside human-like phantoms, as performed through the ESA facility MATROSHKA (MTR) on board the ISS. MATROSHKA is a mannequin equipped with more than 6,000 radiation sensors to allow assessing the exposure of a simulated astronaut's torso to cosmic radiation. The facility was launched to the ISS in January 2004. Up to March 2011, four missions have been accomplished. During the MTR-1 experimental phase (2004-2005) the facility was installed outside the Russian Service Module (Zvezda) simulating a long-duration astronaut space walk. The MTR-2A experimental phase was carried out in the year 2006 inside the Russian docking compartment (Pirs). The third phase (MTR-2B) in the years 2007 to 2009 saw the phantom mounted inside Zvezda, followed by a fourth exposure inside the Japanese Experiment Module from 2010 to 2011 (MTR-2 Kibo).
(See: Figure Summary-1: MATROSHKA-1; Table Summary-1: MATROSHKA-1)
(See: Figure Summary-2: MATROSHKA-2A; Table Summary-2: MATROSHKA-2A)
(See: Figure Summary-1: MATROSHKA-2B; Table Summary-3: MATROSHKA-2B)
HAMLET Project Goals and Project Objectives
To ensure the optimal scientific exploitation of the data generated within the MATROSHKA experiment, the FP7 collaborative project HAMLET (1 September 2008 - 30 September 2011) brought together European experts to process and compile the acquired data and develop a three-dimensional model of the distribution of radiation dose in an astronaut's body. The overall project goals for HAMLET were the following:
* Compilation of data sets from MTR-1, MTR-2A and MTR-2B
This compilation includes the contribution of the European partners (who provided almost 90% of the scientific data) as well as the non-European partners in the MATROSHKA project. The comprehensive inter-comparison and compilation of experimental data acted as input for the proposed radiation transport calculations. The European partners within the HAMLET consortium have extensive experience in either experimental assessment or numerical modelling of the space radiation environment. The group therefore brought together experimental and theoretical researchers working on the common goal of exploring and deepening our knowledge of space radiation effects on the human body.
* Data archive
Strongly interlinked with the data compilation, the build-up of a data archive enabled the community to access the measured and evaluated data from all participating laboratories. This was essential for the achievement of the project goals as it improved the scientific results by incorporating the individually collected data sets into an overall context. This effort permitted straightforward data access and comparison.
* 3D radiation model
A three-dimensional (3D) numerical model of the space radiation dose distribution within the phantom torso has been developed based on experimental data sets. In parallel, a three-dimensional model has been derived from Monte Carlo radiation transport calculations and verified against measurements. This will enable future simulations of tissue and organ doses for radiation risk assessment of personnel on long-term space missions on the ISS, to the Moon or other celestial bodies.
* Public awareness
The presentation of scientific data to the public was strongly emphasized within the project. Raising the public's awareness and understanding, particularly in the well-debated field of health physics and radiological protection, was an essential task. The MATROSHKA experiment gave us a perfect 'tool' by connecting the issues of 'space radiation' and 'radiation received on human missions to the Moon and Mars' with the human perspective, particularly since MATROSHKA is meant to simulate an astronaut in the space environment. This context along with the possibility of generating a 3D dose distribution throughout the human body, was taken as input for the development of public outreach activities, including a public version of the data archive.
According to these goals, the overall objectives were defined as (1) the processing, compilation and combination of dosimetric data from the MATROSHKA experiment; (2) the characterization of the radiation detector response to a well-defined subset of the space radiation environment and harmonization of experimental protocols; (3) the survey and detailed exploitation of available literature on cosmic-ray dosimetry on board the ISS and phantom experiments in space; (4) the development of a three-dimensional voxel model of the MATROSHKA phantom to facilitate the calculation of organ doses and thereby assessing the effective dose as a prerequisite for radiation risk estimation; (5) radiation transport calculations using the Monte Carlo transport code PHITS; (6) the launch of a dedicated HAMLET website and build-up of a database structure for archiving MATROSHKA dosimetric data and (7) the organization of HAMLET Public Outreach Events to inform the public audience about the status of the project.
Within the HAMLET project, these objectives were embedded in five dedicated work packages (WP), with corresponding milestones and deliverables: WP1: Data Processing and Compilation; WP2: Detector Characterization; WP3: ISS Space Data Intercomparison; WP4: Experimental and Calculated 3D Radiation Model; WP5: Dissemination of Results.
* Work Package 1: Objectives
The overall goal of Work Package 1 of the HAMLET project was the compilation and combination of radiation detector data gathered by all groups from the MTR-1, MTR-2A and the MTR-2B experimental phases. These data sets were used as essential input for the development of a 3D model on the basis of measured data and serve as benchmark for the applied data radiation transport codes. The data evaluation and processing was performed both for data generated with passive radiation detectors during all the three mission phases as well as for data generated with active radiation detectors measured during the MTR-1 and the MTR-2B mission phase.
* Work Package 2: Objectives
The aim of Work Package 2 was to characterize the detector systems applied within the MATROSHKA experiment, in terms of their detection properties. Detector characterization was needed in two respects. The first concerned the peculiarity of the conditions encountered by detectors within the MATROSHKA experiment, that is, the complexity of the radiation field and a very long time of exposure. The second requirement for detector characterization came from the great variety of radiation detectors that have been used within the experiment. Each investigator further applied his own measurement and calibration protocols. It was therefore essential to compare performance of detectors and evaluation procedures applied by the individual participants. The main effort of Work Package 2 activities was in characterization of radiation detectors in ground-based radiation fields available from high-energy particle accelerators, which may be considered as a simulation of sub-sets of the space radiation environment. The HAMLET consortium was granted with two research projects by the National Institute of Radiological Sciences (NIRS) in Chiba, Japan, and the ESA European Space Research and Technology Centre (ESTEC) in Nordwiijk, The Netherlands, for using machine time at the Heavy Ion Medical Accelerator (HIMAC) in Chiba and the Heavy-Ion Synchrotron (SIS) of the GSI Helmholtz Centre for Heavy-Ion Research in Darmstadt, Germany. Within the realized five irradiation campaigns at the HIMAC and two at GSI, the detectors were exposed to monoenergetic beams of fully ionized helium, carbon, silicon, neon, argon, iron and nickel nuclei with energies up to 1000 MeV/u.
* Work Package 3: Objectives
Interpretation of the comprehensive MATROSHKA data set compiled within Work Package 1 required putting the scientific output in the context of other research in the field of cosmic radiation dosimetry conducted in parallel with the MATROSHKA experiment. Having analysed the detection principles and response characteristics of the vast suite of active and passive instrumentation previously or currently applied in space, the published scientific literature on phantom studies in space as well as active and passive radiation monitoring conducted on board the ISS from 2004 to present has been reviewed in detail and, finally, compared with the MATROSHKA dosimetric results in order to evaluate their relevance for radiation exposure assessment of astronauts.
* Work Package 4: Objectives
The aim of Work Package 4 was the build-up of a 3D model of the MATROSHKA results based on the data generated within Work Package 1 and the calculation of the dose values within the phantom using Monte Carlo transport codes. As a prerequisite for the numerical model, two computer tomography (CT) scans of the MATROSHKA have been performed. The data from the CT scans were then used to build a voxel model called NUNDO (Numerical RANDO) of the phantom. A computer program OrDoCal (Organ Dose Calculation) was developed for the interpolation of point doses over the whole phantom volume and for calculation of the organ doses based on the data input from Work Package 1. Using this software, the data obtained within the three MATROSHKA experimental phases were analysed and a 3D dose distribution based on the measurements within the phantom was calculated. This 3D dose distribution model enabled determination of effective dose for the three missions and thereby supported for radiation risk estimations. The radiation transport calculations for the MTR-1 and the MTR-2B experimental phases were performed using the three-dimensional multi-purpose particle and heavy-ion Monte Carlo transport code PHITS coupled to the developed voxel phantom NUNDO. For the MTR-1 simulations, the phantom, together with the container, was placed on the aluminium foundation and the inside of the foundation as well as the inside of the container were filled with air. The container together with the foundation, were located on a simplified ISS geometry, represented by an aluminium cylinder. Organ dose and dose equivalent rates were calculated in the NUNDO phantom. Simulations of the MTR-2B experiment inside the ISS were performed in the same way. Simulations of irradiations of the MATROSHKA phantom head at the HIMAC were obtained using the Monte Carlo code packages FLUKA and GEANT4.
* Work Package 5: Objectives
The overall goal of Work Package 5 is the dissemination of results of the HAMLET project. The public outreach of HAMLET was optimized by installation of the HAMLET webpage under http://www.fp7-hamlet.eu. The scope of this page was not only to inform the public about the project itself, but also provide a comprehensive, still concise overview of the space radiation environment, detector instrumentation, numerical modelling and associated topics, and highlight the expertise of the participating institutions. An image gallery serves as an online repository of digital images pertaining to the MATROSHKA experiment and HAMLET activities. Five dedicated Public Outreach Events, hosted and organized at the bases of the participating institutions, helped to further increase the awareness of the public audience to the significance of radiation exposure in view of the future development of human spaceflight. The science achievements of the HAMLET project were disseminated publicly through a web database. Following the definition of a unified structure for the experimental data provided by the individual participants, a front end of the web database has been designed which allowed for convenient and reliable uploading of the processed dosimetric data under http://www.fp7-hamlet.eu/index.php/database. The data archive currently contains absorbed dose rates measured under extravehicular activity (EVA) conditions during the MTR-1 experiment by miniature luminescence detectors at about 4,800 sites within the anthropomorphic phantom body. The user is graphically assisted in navigating through the torso. The database will be updated upon publication of the final results of the HAMLET project.
Project Results:
Introduction
The astronauts and cosmonauts working and living in a space station at altitudes of ~400 km are exposed to radiation levels far exceeding the natural radiation environment on ground. The three main radiation components in low-Earth orbit (LEO) are galactic cosmic rays (GCR), emissions from the Sun - either solar particle events (SPE) or coronal mass ejections (CME) - and protons and electrons trapped in the Van Allen belts. In LEO, albedo neutrons and protons can also be found that are produced when GCR particles interact with the atmosphere and travel along trajectories reflecting them back into space. The contribution of these sources to the radiation load on humans on board a space station varies greatly and depends on various parameters such as the orbital inclination and altitude, the shielding distribution of the spacecraft and the solar cycle. Contrary to the radiation environment on Earth, the main contribution to the radiation exposure arises from heavy charged particles encountered in GCR and protons emitted by the sun. Due to their high energies, these primary particles can easily penetrate a spacecraft wall, thereby creating a secondary radiation field, which includes neutrons. The radiation load on humans in space can therefore reach levels that are up to a factor of 100 times greater than those present on Earth, giving the space-faring nations a legal and moral obligation to monitor the radiation exposure of space travellers, particularly for long-duration missions. Data from active and passive radiation monitoring act as input for risk estimates of cancer induction, attributed to the high radiation level. Since the internal organs of the human body are more sensitive to penetrating radiation than the skin, the determination of organ doses is an essential aspect. Measurements are only possible by applying anthropomorphic phantoms that allow integration of radiation detectors inside a simulated human body.
The Radiation Biology Department of DLR developed the anthropomorphic phantom experiment MATROSHKA. The MATROSHKA facility is an ESA experimental unit for studies of the depth dose distribution through the different components of the LEO radiation field at the sites of specified organs. MATROSHKA consists of a human head/torso phantom, allowing accommodation of dedicated active and passive radiation measurement devices. The objective of the MATROSHKA experiment is to determine the empirical relations between measurable and tissue absorbed doses in a realistic human phantom exposed to cosmic radiation. Such measurements have the highest priority, particularly in view of long-term human space exploration. Once the ratio between surface and tissue/organ doses is known for a particular radiation field, it may be used in future exposures to determine the required tissue/organ doses from measurements of just the surface dose, which are much easier to perform. The collected data will be used to reduce the uncertainties of risk projections of radiation-induced cancer and to refine shielding structures in future space missions.
The MATROSHKA facility basically consists of a human phantom upper torso, a base structure and a container with a total mass of about 65 kg. The phantom torso and container are mounted to the base structure, which serves as a footprint for the human mannequin. The container consists of a carbon fibre structure, forms together with the base structure a closed volume which is filled with a dry oxygen atmosphere at ambient pressure and protects the phantom against space vacuum, debris, solar UV and material off-gassing. It provides approximate the same shielding thickness as an Astronaut's space-suit does. The phantom body is made of natural skeleton embedded in tissue equivalent polyurethane w of different densities for tissue and lungs, well introduced in the field of radiotherapy. It consists of 33 slices, each with a thickness of 25 mm. The phantom slices are equipped with channels and cut-outs to allow the accommodation of active and passive dosemeter systems as well as temperature and pressure sensors (housekeeping data). A total number of six temperature sensors, three of them in the phantom torso at slices #2 (head), #16 (upper torso) and #26 (lower torso) and three in the base structure as well as two pressure sensors allow recording of temperature and pressure profiles in the facility. Besides the dose determination inside the body, the torso is also equipped with a poncho and a hood equipped with radiation detectors for skin dose measurements. The cables indicate the positions of the silicon scintillation detectors (SSD) at selected organ sites. A DOSimetry TELescope (DOSTEL) is mounted on top of the head, while a tissue -equivalent proportional counter (TEPC) is installed in front of the upper body on the base structure.
The 33 slices of the phantom are equipped with 356 channels for accommodation of thermoluminescence dosemeters (TLDs) from the participating groups at a total of 1634 positions arranged in a one-inch grid throughout the body. The TLD chips are kept in tubes with tissue-equivalent spacers. At each of the 1634 points, between two and six dosemeters of different thermoluminescence (TL) phosphors are located, e.g. a combination of 6LiF:Mg,Ti, 7LiF:Mg,Ti and 7LiF:Mg,Cu,P. Besides determination of the absorbed dose, this configuration also permits information about the thermal and epithermal neutron dose to be obtained using the so-called pair method. Except for the TLDs contained in the 33 slices, the phantom has five cut-outs for installation of nuclear track detector packages (NTDP), sized 55 x 35 x 21 mm, to measure the absorbed dose to the eye, lung, stomach, kidney and intestine. Each of these boxes is equipped with a combination of sixty TLDs and plastic nuclear track detectors (PNTDs), the latter being arranged orthogonally to enable assessment of linear energy transfer (LET) and charge spectra in three perpendicular axes. Further, the packages contain PNTDs covered by converter foils to evaluate the neutron organ doses. The poncho and the hood are equipped with polyethylene stripes with sewed-in TLDs to measure the skin dose around the entire torso. The poncho is further equipped with six NTDP packages in similar dimensions as used at organ sites (two in the front, two in the back and one on each side of the torso) to support the skin dose measurements. On top of the phantom head a NTDP as well as the silicon telescope DOSTEL are located. Inside the torso, at the sites of particular organs active SSDs (plastic scintillators covered by silicon diodes operated in anti-coincidence mode) are placed next to an NTDP.
(See: Figure Introduction-1: MATROSHKA-Facility)
(See: Figure Introduction-2: MATROSHKA-Detectors)
To ensure the optimal scientific exploitation of the data generated within the MATROSHKA experiment, the FP7 collaborative project HAMLET (1 September 2008 - 31 August 2011) brought together European experts to process and compile the acquired data and develop a three-dimensional model of the distribution of radiation dose in an astronaut's body. In particular, the project objectives were (1) the processing, compilation and combination of dosimetric data for the MATROSHKA experiment; (2) the characterization of the applied radiation detector response to a well-defined subset of the space radiation environment and harmonization of experimental protocols; (3) the survey and detailed exploitation of available literature on cosmic-ray dosimetry on board the ISS and phantom experiments in space; (4) the development of a three-dimensional voxel model of the MATROSHKA phantom to facilitate the calculation of organ doses and assess effective dose as a prerequisite for radiation risk estimations; (5) radiation transport calculations using the Monte Carlo transport code PHITS; (6) the launch of a dedicated HAMLET website and build-up of a database structure for archiving MATROSHKA dosimetric data and (7) the organization of HAMLET Public Outreach Events to inform the public audience about the status of the project.
The main scientific results of the HAMLET project, embedded in five dedicated work packages (WPs) with corresponding milestones and deliverables (WP1: Data Processing and Compilation; WP2: Detector Characterization; WP3: ISS Space Data Intercomparison; WP4: Experimental and Calculated 3D Radiation Model; WP5: Dissemination of Results) will be outlined in the following sections.
WP1: Data Processing and Compilation
The overall goal of Work Package 1 of the HAMLET project was the processing, compilation and combination of data acquired by the participating laboratories from TLD and PNTD measurements during the MTR-1, MTR-2A and MTR-2B experimental phases. These data sets were used as essential input for the development of a 3D model on the basis of measured data and serve for benchmarking the radiation transport codes (see also Work Package 4). In addition Work Package 1 was devoted to the analysis of data generated with the active radiation detectors during the MTR-1 and MTR-2B experiment phase.
Thermoluminescence detectors: For the determination of the absorbed dose from ionizing radiation the HAMLET collaboration applied passive TLDs of various types. The energy deposited by ionizing radiation in these detectors is stored at defect centres in the crystal lattice and released in the form of light upon heating in the laboratory (readout) yielding the so-called glow curve. The emitted light is proportional to the absorbed dose, thus enabling TLD utilization in radiation dosimetry upon calibration in gamma-ray fields. Due to their small size of around 3 x 3 x 1 mm3 and mass of around 20 mg TLDs have been applied for radiation measurements on board various space stations and Space Shuttles since the beginning of the space age. The TLDs providing the basis for measurement of the spatial dose distribution within the MATROSHKA torso were embedded in polyethylene tubes. A total number of 356 TLD tubes was used in the 33 slices of the phantom. All the slices with even numbers were equipped with TLDs from HAMLET partner IFJ-PAN, Krakow, Poland, while the odd-numbered slices were shared by the HAMLET partners TUW, Vienna, Austria, and DLR, Cologne, Germany. In total, this amounts to 784 measurement points for IFJ-PAN, 405 for DLR and 407 for TUW resulting in a total number of 1596 discrete measurement points for the build-up of the three-dimensional dose distribution model of the MATROSHKA experiment. The build-up of the discrete 3D dose distribution using data from passive thermoluminescence detectors for the first three MATROSHKA experimental phases is shown in the following figures: Figure WP1-3: MTR-1 3D (for the MTR-1 experimental phase accomplished outside the ISS); Figure WP1-4: MTR-2A 3D (for the first intravehicular exposure MTR-2A in the Russian Pirs module) and Figure WP1-5: MTR-2B 3D (for the second intravehicular experiment MTR-2B in the Russian Zvezda module). These three figures show in detail how the discrete dose distribution is built up using the data from thermoluminescence detectors supplied by the HAMLET partners DLR, IFJ-PAN and TUW.
(See: Figure WP1-3: MTR-1 3D)
(See: Figure WP1-4: MTR-2A 3D)
(See: Figure WP1-5: MTR-2B 3D)
Figure WP1-6: MTR - All missions 3D shows the comparison of the discrete 3D absorbed dose distribution measured for the three MATROSHKA experimental phases (MTR-1, MTR-2A and MTR-2B) on the basis of more than 4800 thermoluminescence detector measurements for each mission. It is evident that the absorbed dose determined for the extravehicular MTR-1 mission ranged between 0.5 and 0.1 mGy/day, going from the skin to the inner parts of the body, while both the dose range and gradient for the intravehicular exposures were considerably lower (0.23 to 0.13 mGy/day for MTR-2A and 0.21 to 0.14 mGy/day for MTR-2B, respectively). The decrease in absorbed dose at the surface and the upper parts of the body is due to the higher shielding inside the ISS, which reduces primarily the dose delivered by low-energetic protons when crossing the South Atlantic Anomaly. In contrast, the dose at deeper organs - mostly arising from GCR - was nearly constant despite the different exposure conditions in- an outside the space station. The reason for this is found in the high energy of the GCR component and in the self-shielding of the body.
(See: Figure WP1-6: MTR - All missions 3D)
The data generated by the thermoluminescence detectors -located either inside the phantom for the measurement of the discrete 3D absorbed dose distribution map oron the surface of the phantom for the measurement of the skin dose as well as in dedicated organs for the measurement of the organ dose - is further processed in Work Package 4 when building up a continuous dose distribution map for the MATROSHKA experimental phases.
Nuclear Track Detectors: A second type of passive detectors applied within the MATROSHKA experiment were plastic nuclear track detectors (PNTDs) also known as CR-39 detectors. Upon traversal of a heavy charged particle the molecular bonds of the material are broken, thereby producing a latent track. After etching in a caustic solution this nanometre-sized tracks are widened and can be observed under an optical microscope. Based on the calibration of the applied detectors at ground-based accelerator facilities (see also Work Package 2), it is possible to deduce the absorbed dose and the dose equivalent of the heavy ion contribution by measuring dedicated track parameters.
(See also: Figure WP1-7: MTR CR-39)
The data generated by nuclear track detectors - located either on the surface of the phantom for the measurement of the skin dose or in dedicated organs for the measurement of the organ dose - were further combined in Work Package 4 with the data from thermoluminescence detectors in order to calculate the organ doses and, from these values, the effective dose, which is a prerequisite for radiation risk assessment.
Besides the passive radiation detectors also active radiation detectors where used within the MTR-1 and MTR-2B missions, most notably the DOSimetry TELescope (DOSTEL) mounted on top of the head of the MATROSHKA facility.
Active Detectors: The DOSTEL instrument is based on two identical passivated implanted planar silicon (PIPS) detectors produced by Canberra Semiconductors; it was designed to measure the energy deposited by charged particles. One detector has a nominal thickness of 300 µm and the other one a thickness of 150 µm. Both detectors have a sensitive area of 693 mm². They are mounted in a distance of 15 mm, forming a telescope with a geometric factor of 824 mm² sr for particles arriving from the front. The MTR-DOSTEL measures count rates in 100- or 20-second time resolution as well as energy deposition spectra, which are integrated over 45 minutes. In case of high count rates, for example during crossings of the South Atlantic Anomaly (SAA), the instrument switched to SAA mode and records an additional energy deposition spectrum. The integration period of these SAA energy deposition spectra depended on the time duration of high count rates.
The energy deposition spectra measured mode was used to calculate the mean quality factor. This factor describes the biological effectiveness of radiation. With this information and the knowledge of the total absorbed dose in the detectors it is possible to derive the dose equivalent (which serves as substitute for effective dose).
As an example of the results generated with the DOSTEL Figure WP1-8: DOSTEL-1 shows the DOSTEL count rates measured in the silicon detector for a two-day time interval in May 2004. This count rate plot can further be evaluated by the correlation of the count rate with the ISS orbit, resulting in a 2D count rate plot versus longitude and latitude as given in Figure WP1-9: DOSTEL-2. This count rate plot over the orbit of the space station highlights the passage for different time periods as well as the change in radiation environment conditions over time and orbit of the space station and clearly shows the increase in count rate with increasing longitude and the high count rates due to the low-energetic protons while crossing the South Atlantic Anomaly over the coast of Brazil.
A summary of the absorbed dose and dose equivalent values determined with the DOSTEL instrument for the MTR-1 mission outside the ISS is given in
Table WP1-1: DOSTEL-MTR-1, while the results for the inside exposure during the MTR-2B mission are given in Table WP1-2: DOSTEL-MTR-2B. The results clearly indicate the high difference in dose equivalent due to the crossing of the South Atlantic Anomaly (367 µSv/day for the MTR-1 mission in comparison to 72 µSv/day for the
MTR-2B inside mission) and the quite similar contribution from GCR (245 µSv/day for the MTR-1 mission in comparison to 310 µSv/day for the MTR-2B mission).
(See also: Figure WP1-8: DOSTEL-1)
(See also: Figure WP1-9: DOSTEL-2)
(See also: Table WP1-1: DOSTEL-MTR-1)
(See also: Table WP1-2: DOSTEL-MTR-2B)
Since the results - especially for the passive radiation detectors within the MATROSHKA missions - are comprised of data generated by various research groups from all over the world, with 95% of the detectors provided by the HAMLET partners, the essential prerequisite for the combination and comparison of these results was that the relevant detector properties for the applied detector systems were known sufficiently well. This information has been gathered within Work Package 2 of the HAMLET project.
WP2: Detector Characterization:
The aim of Work Package 2 was to characterize the detector systems applied within the MATROSHKA experiment, in terms of their detection properties. The detector characterization was needed in two respects. The first concerned the peculiarity of the conditions encountered by detectors within the MATROSHKA experiment, that is, the complexity of the radiation field and a very long time of exposure. The second requirement for detector characterization came from the great variety of radiation detectors that have been used within the MATROSHKA experiment. Each of the investigators also applied their own measurement and calibration protocols. It was therefore essential to compare performance of detectors and evaluation procedures applied by individual participants to have full understanding of the detector properties and to use this information for the combination of data as performed in Work Package 1.
The main effort of Work Package 2 activities was in the characterization of radiation detectors in ground-based radiation fields available from high-energy particle accelerators, which may be considered as a simulation of sub-sets of the space radiation environment. The HAMLET consortium was granted with two research projects by the National Institute of Radiological Sciences (NIRS), Chiba, Japan and the ESA European Space Research and Technology Centre (ESTEC), Nordwiijk, The Netherlands, for using machine times at the Heavy Ion Medical Accelerator (HIMAC) at NIRS in Chiba, Japan, and the Heavy-Ion Synchrotron (SIS) of the GSI Helmholtz Centre for Heavy-Ion Research in Darmstadt, Germany, as shown in Figure WP2-1: HIMAC-GSI. Within the realized five irradiation campaigns at the HIMAC and two at the GSI, the detectors were exposed to the monoenergetic beams of fully ionized helium, carbon, silicon, neon, argon, iron and nickel nuclei with energies up to 1000 MeV/u.
(See also: Figure WP2-1: HIMAC-GSI)
Due to an international cooperation of DLR with NASA it was further possible to irradiate detectors with protons of energies up to 450 MeV in order to simulate a solar particle event in the NASA Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory (BNL), Upton, NY, USA, as shown in Figure WP2-2: NSRL.
(See also: Figure WP2-2: NSRL)
One focus of the accelerator experiments was the comparison of the response of thermoluminescence detectors (TLD) applied by the HAMLET partners TUW, Vienna, Austria, DLR, Cologne, Germany and IFJ-PAN, Krakow, Poland, within the MATROSHKA experiment. TLDs are solid-state passive dosimeters, their principle of operation being the emission of light upon heating following the previous absorption of radiation energy. The amount of emitted light is a measure of the absorbed dose. The relative radiation detection efficiency of a particular TLD phosphor depends on the ionization density, so it is different for densely ionizing particles and for sparsely ionizing gamma-rays, which are commonly used for calibration. While the occurence of these effects was in principle known, the existing knowledge on this subject was mostly general and qualitative. Analysis of the MATROSHKA data required systematic quantitative investigations of the dependence of thermoluminescence efficiency on radiation type and ionization density, for actual detector types, which were used in space. Some of the obtained results are illustrated in Figure WP2-2: TLD -1 and
Figure WP2-2: TLD -2. The main conclusion from these results is that there is a very good agreement between the different laboratories, in spite of differences of detectors origin and evaluation methods. It also very important, that for all investigated types of detectors, the dependence of the termoluminescence efficiency on LET for high-energy ions may be described by a unique empirical function. This is a remarkable finding, as in general (i.e. considering the full energy range), the dependence of efficiency on LET splits into many branches, corresponding with different ion charges. Thus, in case of cosmic radiation, which is dominated by high-energy ions, it was possible to use functions correcting TL efficiency.
(See also: Figure WP2-2: TLD -1)
(See also: Figure WP2-2: TLD -2)
Another type of the studied detectors were the nuclear track etch detectors (NTD). They permit to determine the radiation dose above a given threshold value of ionization density, parameterized by LET (linear energy transfer), depending on type of the detector material and the evaluation method. To visualize the latent tracks induced in the detector sheets by the different ionizing particles a chemical etching procedure is applied. The detectors are evaluated after etching by an image analyser system, which recognizes the tracks and measures their geometrical and optical parameters, which allow obtaining the track etch rate ratio (V) for each particle. V is converted into LET using the appropriate calibration functions and then the dose can be calculated from the LET spectra. A calibration function can be determined by exposing detectors with particles of known charge Z, mass M, energy E and LET. Determining of such calibration curves was one of the goals of the WP2 investigations. An example of a calibration curve is given in the Figure WP2-4: CR-39. The HIMAC investigations enabled also evaluation of the angular dependence of NTD efficiency.
(See also: Figure WP2-4: CR-39)
The third type of detectors studied with the high-energy ion beams were "Silicon-Scintillator Devices" (SSD) operated by HAMLET partner CAU, Kiel, Germany which have been positioned inside various organs within the MATROSHKA experiment. The SSD detectors consists of an organic scintillator fully covered by semiconductor photo diodes. The scintillator is used to measure charged particles as well as neutrals. To distinguish charged and neutral particles the photo diodes are used since they are also detecting charged particles directly.
(See also: Figure WP2-5: SSD)
Besides the calibration and efficiency studies, in frame of the irradiation campaigns at the accelerator centres, also exposures of the head of the MTR phantom were realized. In this way, the dose distributions inside the head were measured for various ions, as given in
Figure WP2-6: HIMAC - Depth Dose, which were further used for serve as benchmark of the computer transport codes in Work Package 4.
(See also: Figure WP2-1: HIMAC-GSI)
(See also: Figure WP2-6: HIMAC - Depth Dose)
Another study realized within the Work Package 2 was devoted to the investigation of long term stability of the performance of thermoluminescence detectors - taking into account the very long duration of the various MATROSHKA phases. This study was accomplished at IFJ, Krakow, Poland and consisted of the over one-year storage of various types TLDs, with irradiations realized at different times during the storage period. Two storage temperatures (room temperature and -18°C) and two radiation modalities (gamma-rays and thermal neutrons) were used. Results showed that there are no significant instabilities of TLD signals.
For a precise comparison of measured data it is necessary to prove, that also the calibration performed by the various research groups is consistent. For this an intercomparison experiment was realized, in which TLDs from DLR, TUW and IFJ were exposed to gamma calibration doses in each of the three participating laboratories. The results of this experiment show that agreement between calibration factors used by different groups is better than 3%.
(See also: Figure WP2-6: TLD - Properties).
Work Package 2 and the relevant results gathered within this Work Package proofed, that the combination of the measured data from the different groups from the MATROSHKA space experiments can be pooled together to construct a 3 D dose model.
WP3: ISS Space Data Intercomparison
In view of exploiting the maximum possible information regarding projection of acute and late radiation risks for space travellers on current and future missions of exploration, it did not seem appropriate to treat MATROSHKA as a stand-alone investigation, but rather put its outcome into the context of other radiation measurements conducted in timely parallel. For that to be done deserved particular attention to be paid to the instrument responses and detection principles in order to facilitate cross-comparison and harmonization of the measured data.
On the HAMLET website, a reference database has been set up and updated frequently to enable public access of all articles published in topical journals of the Science Citation Index or presented at international conferences that are related to space-borne phantom experiments and radiation measurements on board the ISS since launch of its first components in 1998 (Figure WP3-1: HAMLET-Database-Literature). The papers are linked to by categories and the ISO-standardized Digital Object Identifier system. As with 30 September 2011, the subcategories contained the following number of references grouped by instrument:
* Active radiation monitoring: 81 articles (including supplementary publications)
* Passive radiation monitoring: 79 articles (including supplementary publications)
* Phantom experiments: 42 articles (including supplementary publications)
(See: Figure WP3-1: HAMLET-Database-Literature)
The subsection "Active radiation monitoring" addresses instrumentation used for area dosimetry and science-driven experiments, which is based on silicon detector and ionization chamber principles, such as
* ALTEA detector suite
* Bonner Ball Neutron Detector
* Charged-Particle Directional Spectrometer
* DB-8 silicon detector
* Dosimetry Telescope
* Liulin Mobile Dosimetry Unit
* R-16 ionization chamber
* Sileye-3/Alteino silicon strip telescope
* Tissue-Equivalent Proportional Counter
* TriTel silicon telescope
The entries under the subsection "Passive radiation monitoring" comprise references to measurements applying to area and personal dosimetry as well as science-driven investigations as:
* Nuclear and superheated emulsions
* Thermally and optically stimulated luminescence dosimeters
* Nuclear track detectors
* Combinations of the above methods
Under the category "Phantom experiments" publications related to various phantoms experiments as:
* Phantom head and torso "Fred" flown by NASA on the Space Shuttle and the ISS
* Russian spherical phantom experiment on board the Mir orbital station
* Polyurethane-based spherical phantom MATROSHKA-R installed in the Russian Segment of the ISS
have been listed. A selection of review and supplementary papers in each category should support understanding of the detector principles and calibration as well as interpretation of experimental results.
As it turned out, only those investigations related to area monitoring or science-driven experiments were of relevance to MATROSHKA, which had been conducted in the same segment of the ISS, be it either the Zvezda Service Module or the less shielded Pirs Module.
(See: Table WP3-1: Space Experiments)
For all other studies, in particular measurements outside the station, the very different shielding configurations did not allow for meaningful cross-comparison. The dose rates measured at the surface of the MATROSHKA facility during MTR-2A in Pirs and MTR-2B in Zvezda, respectively, proved to be in overall agreement with data evaluated from Pille-MKS thermoluminescence dosimeter measurements, which are the backbone of area monitoring on board the Russian Segment of the ISS (Figure WP3-2: PILLE -Results). Dose distributions determined in the MATROSHKA-R spherical phantom showed a high level of both qualitative and (particularly for the heavier shielded Service Module) quantitative consistency with the skin and depth dose profile measured in the anthropomorphic MATROSHKA mannequin (Figure WP3-3: MTR-Skin dose).
(See: Figure WP3-2: PILLE -Results)
(See: Figure WP3-3: MTR-Skin dose)
WP4: Experimental and Calculated 3D Radiation Model
For this work package two computer tomography (CT) scans of the MATROSHKA phantom were first performed. The data from the CT scans were then used to build a Voxel model called NUNDO (Numerical RANDO) of the phantom. Figure WP4-1: CT-Model shows the real MATROSHKA phantom and the CT scans of it, the Voxel phantom NUNDO. The material density of the skeleton is equal to 1.3 g/cm3.
(See: Figure WP4-1: CT-Model)
After that a computer program, OrDoCal (Organ Dose Calculation), was developed for the interpolation of the discrete 3D point dose measurements over the whole phantom volume and for calculation of the organ doses based on the data input from Work Package 1. Using this software, the data obtained within the three MATROSHKA experiment phases experiment were analyzed and a 3D dose distribution based on the measurements within the phantom was calculated. The relevant continuous 3D dose distributions are given in Figure WP4-2: MTR-1 3D for the MATROSHA-1 exposure outside the ISS; in Figure WP4-3: MTR-2A 3D for the 1st inside exposure in the PIRS module and in Figure WP4-4: MTR-2B 3D for the 2nd inside exposure in the Zvzeda module.
(See: Figure WP4-2: MTR-1 3D)
(See: Figure WP4-3: MTR-2A 3D)
(See: Figure WP4-4: MTR-2B 3D)
Clearly seen in the comparison of the three figures is the high dose gradient for the MTR-1 outside exposure from the skin to the inner organs due to the high contribution of electrons and protons from the South Atlantic Anomaly. Due to shielding of the International Space Station this contribution is reduced and the gradient is way flatter for the inside exposures. Based on the development of the NUNDO phantom it is now possible to include the organs inside the continuous 3D dose distribution and calculate the relevant organ absorbed doses as given in Figure WP4-5: MTR Organ Absorbed Dose for the three MATROSHKA missions. Adding the data from the nuclear track etch detectors one can further calculate the organ dose equivalents as given in Figure WP4-6: MTR Organ Dose Equivalent. With this information the effective dose for the three MATROSHKA mission could be calculated and is given in Figure WP4-7: MTR Effective Dose.
(See: Figure WP4-5: MTR Organ Absorbed Dose)
(See: Figure WP4-6: MTR Organ Dose Equivalent)
(See: Figure WP4-7: MTR Effective Dose)
The results for the effective dose, which is pre-requisite for the calculation of the radiation risk for long duration space missions, indicate an effective dose of 0.69 mSv/day for the outside exposure and a variation of the effective dose from 0.53 to 0.57 mSv/day for the exposures inside the Russian part of the International Space Station.
The radiation transport calculations for the MTR experiments were performed using the 3D multi-purpose particle and heavy ion Monte Carlo transport code PHITS coupled to the constructed Voxel Phantom NUNDO. The external space radiation environment was calculated with models from the CREME96 and SPENVIS model packages. For the MTR-1 simulations, the phantom, together with the container, was placed on the aluminium foundation of 1 g/cm2 thickness and the inside of the foundation as well as the inside of the container were filled with 1 atm. air. The container was made of 0.35 g/cm2 of carbon fibre composed by hydrogen (4.2%), carbon (42.2%), oxygen (4.2%), nitrogen (28.5) fluorine (8.4) silicon (11.7) chlorine (0.6) and sulphur (0.3). The container together with the foundation, were located on the simplified ISS geometry, chosen as an aluminium cylinder shape with a thickness of 15 g/cm2, as shown in Figure WP4-8: MTR-1 Simulation Set up.
(See: Figure WP4-8: MTR-1 Simulation Set up)
Everything was placed in a spherical radiation source where the particles were emitted inward and isotropically. Heavy ions with atomic numbers up to 28 and energies up to 100 GeV/n were considered in the GCR, and GCR fluxes were from year 2004, where the apogee 365 km, perigee 345 km and inclination 52o approximated the ISS flight path. During the MTR experimental period, February 2004 to October 2005, the solar activity gradually decreased from solar maximum to solar minimum, so the TP component of the cosmic radiation described by the AP-8 model for minimum solar activity was here adopted.
The phantom and results of simulations of the measurements performed with TLDs in tubes 3B, 4B and 5A located in the head region (marked with a red rectangle) of the phantom is shown in Figure WP4-9: Simulation Results 1. Both, the simulated and experimental data are given as doses in water, with TL efficiency corrections. Simulations were performed separately for Trapped Protons (TP) and Galactic Cosmic Radiation (GCR), and the total dose is given as the sum of the TP and GCR contributions. The comparison for all the measured 3D dose data with the simulated data is given in Figure WP4-9: Simulation Results 2.
(See: Figure WP4-9: Simulation Results 1)
(See: Figure WP4-9: Simulation Results 2)
The absorbed dose in each organ of the phantom NUNDO was defined as the total energy deposited in the organ divided by the mass of this organ. The dose equivalent was calculated with calculated according to the Report 60 of the International Commission on Radiological Protection. Simulations of the organ doses and the dose equivalents were done separately for TP, GCR and Trapped Electrons (TE). The calculated organ dose and dose equivalent rates for MTR-1 experiment are summarized and compared to the corresponding experimental data in Figure WP4-10: Organ Dose and Table WP4-1: Organ Dose. The simulated results are both shown as the sum of all radiation components contributed to the total dose (GCR, TP and TE), and when the TE component is subtracted, to clearly show the significance of TE on the most outer tissue doses. The TE contributions are negligibly small to the doses deep inside the human body, since the energies of the trapped electrons are so low that they generally stop very close to the surface of the body. When comparing the simulated data with the MTR experimental results, the agreement is good for the inner structures but rather large discrepancies are observed for the most outer organs, like skin or breast due to an underestimation of the container thickness. The disagreement of the calculated outer organ doses with the experimental values suggested that the container thickness of in our simulations was too thin compared to the experimental setup, where additional NOMEX® poncho and multilayer insulation covered the phantom. To check how the container thickness influences the results, additional simulations with the same geometry but with a thicker container were performed. These simulations gave better agreement between the simulated and measured dose for the outer organs, e.g. the skin.
(See: Figure WP4-10: Organ Dose)
(See: Table WP4-1: Organ Dose)
Simulations of the MTR-2B experiment, inside the ISS, were also performed. In
Figure WP4-11: MTR-2B Simulation Set up, the geometry of the phantom, container and foundation (a), and the simplified geometry of the ISS module with the phantom (b), is shown. However due to large uncertainties in the shielding (wall thicknesses, experimental racks, etc.), the simulated doses underestimated the measured ones as given in
Figure WP4-11: Organ Dose MTR-2B.
(See: Figure WP4-11: MTR-2B Simulation Set up)
(See: Figure WP4-11: Organ Dose MTR-2B)
To summarize WP4, simulations of the MTR-1 and MTR-2B were performed with the PHITS code, and the organ dose and the dose equivalent rates were calculated. Comparison to the experimental data taken during the MTR-1 experiment, simulating an EVA, showed a good agreement for the inner organs, considering all the approximations, uncertainties in the geometry of the ISS, and the measured data. The simulated doses in the outer organs had a larger disagreement with the measured values, than for the inner organs due to a strong dependence of the thickness of the container to the dose levels in these outer structures. Since measurements were performed with passive detectors over a long time period, there were changes of local shielding inside the ISS, altitude and phase in the solar cycle during the measurements. As the MTR-1 experiment was performed during a long time period, 1.5 year, it is most probably not enough to only adopt the fluxes from 2004, as done in this study. It would have been more correct to make averages of the energy spectra of GCR and TP at solar minimum and maximum conditions. The performed study showed that the best agreement between the simulated and measured doses was obtained for a container thickness of above 0.35 g/cm2 but below 0.7 g/cm2. This study also showed that the contribution from the TP component to the total dose and the dose equivalent decreases with the depth in a phantom, when outside the ISS, and when calculating the mean values for the solar minimum and the solar maximum activities. The GCR dose and the dose equivalent values increase 20% when the mean dose values for the solar minimum and the solar maximum are calculated comparing to the dose values calculated from the spectra from 2004. A higher altitude does not significantly change the dose contribution from the GCR during an EVA.
The simulations performed for MTR-2B, simulating an IntraVehicular Activity (IVA), deviated more from the measured values than for MTR-1, most likely due to the oversimplified geometry used in these simulations.
In addition to the simulations of the MTR phantom in space with PHITS, simulations of irradiations of the head of MTR phantom performed at the HIMAC accelerator in Chiba, Japan, was performed with the 3D multipurpose particle and heavy ion transport package GEANT4 resulting in very good agreement between the measured and calculated results. These results confirm the importance to know the local shielding configuration in detail when performing simulations of experiments on board the ISS.
WP5: Dissemination of Results:
The overall goal of Work Package 5 was the dissemination of the results of the HAMLET project to the scientific community as well as the public audience.
The presentation of scientific data to the public audience was strongly emphasized within the HAMLET project. Raising the public awareness and educating the audience, especially in the well-debated field of radiation, was taken as an essential task. The HAMLET project gives us a perfect 'tool' by connecting the issues of 'space radiation' and 'radiation on manned flights to Moon and to Mars' with the human 'subjects', especially considering that MTR simulates a human in the space radiation environment.
The Public Outreach of HAMLET was optimized by installation of the HAMLET web page under http://www.fp7-hamlet.eu. The scope of this page is not only to inform the public about the project itself, but rather provide a comprehensive but concise overview of the space radiation environment, detector instrumentation, radiation transport models and associated topics, and highlight the expertise of the participating institutions. An image gallery serves as an online repository of digital images pertaining to the MATROSHKA experiment and HAMLET activities.
Five dedicated Public Outreach Events, hosted and organized at the bases of the participating institutions, further increased the awareness of the public audience to the significance of radiation exposure for the future development of human spaceflight.
http://www.fp7-hamlet.eu/index.php/public-outreach-days/general-information
The science achievements of the HAMLET project are disseminated publicly through a web database. Following the definition of a unified structure for the experimental data provided by the individual participants, a front end of the web database has been designed which allows for convenient and reliable uploading of the processed dosimetric data under
http://www.fp7-hamlet.eu/index.php/database. The data archive currently contains absorbed dose rates measured under extravehicular activity (EVA) conditions during the MTR-1 experiment by miniature luminescence detectors at about 4,800 sites within the anthropomorphic phantom body. The user is graphically assisted in navigating through the torso. The data archive will be expanded in the future with data from the MTR-2A and MTR-2B experiment phases, as well as with the data from the active radiation detectors upon publication of these results in scientific journals.
(See: Figure WP5-1: HAMLET-Science-Database)
(See: Figure WP5-2: HAMLET-Science-Database II)
Besides the presentation of the data generated within the HAMLET project on the HAMLET webpage in the frame of the web database big emphasises was laid on the presentation of scientific data related to the four HAMLET Work Packages at numerous conferences, workshops and seminars over the lifetime of the HAMLET project. The outcome was further presented in peer reviewed publications.
Potential Impact:
Introduction
The main purpose of science is the increase of knowledge to help mankind. Knowledge, based on international joined experiments in space, can only be increased by the close cooperation of the participating investigators. If this cooperation is not strongly emphasized, the community will miss vast amounts of collected experimental data which will be lost for science, and therefore for the advancement of knowledge. The goal of the HAMLET project as described in the HAMLET Mission Statement implements in detail these thoughts.
"The aim of HAMLET is the effective scientific exploitation of data obtained from the ESA MATROSHKA project. This will be achieved by bringing together leading European scientists in the field of space dosimetry to increase and enhance the output of the project and present it to the European scientific community as well as the public audience."(HAMLET MISSION STATEMENT)
Scientific endeavours like the MATROSHKA project are only possible with strong international cooperation. HAMLET includes seven European research institutes all of whom participate in the MATROSHKA project. MATROSHKA is the largest international research initiative ever performed in the field of space dosimetry and combines the expertise of leading research institutions around the world. It consequently generates an extensive pool of data of exceptional value to the scientific community. This potential can only be fully utilized by close cooperation and extensive joint research actions of the investigating groups. Individually, all groups produced valuable scientific data sets, but only the strong cooperation and close integration of multiple, highly skilled scientific groups, leads to the acquisition of new and important knowledge about the effects of space radiation on the human body. The goal of HAMLET was therefore not the local or national organization of expert scientists, but the building of cooperation on a European scale, to utilize the collected data to greatly advance the field of space dosimetry. The long-term MATROSHKA experiment is an exceptional chance for scientific advancement in the field of space dosimetry, and as such, the scientific community shall aim to extract the maximum information from its output. European
"Current space exploration programmes, in Europe and elsewhere, intend to extend the human presence, in a real or virtual way, through missions to the Moon and to Mars or through automatic missions in direction to objects of the solar system." (European Commission- FP7 Call)
The exploration of space as seen in specific projects from ESA within the Aurora Programme, for example, the search for life on MARS (EXOMARS) or other initiatives such as the further exploration of the Moon, act as groundwork for human long duration space missions. However, one of the main constraints for long duration human missions in space, besides the psychological factors and the impact of microgravity on the human physiological system, is radiation. The radiation load on astronauts and cosmonauts in space (as for the ISS) is a factor of 100 higher than on earth. This radiation load will further increase should humans travel to MARS. In preparation for long duration space missions it is important to ensure that ESA has an excellent capability to evaluate the impact of space radiation in order to secure the safety of the astronaut/cosmonaut and minimize their risks. It is therefore essential to gather and focus all possible knowledge in terms of space radiation experiments to enable future generations to travel where nobody has gone before.
Dissemination & Exploitation of Results
The dissemination of the research results is one of the key concerns of the HAMLET project. As a general rule, all the knowledge gained through realization of the HAMLET project is open and available to the scientific community and public alike. A strong intention of the project consortium was the public availability of not only the summary of the main results, as is usual in scientific articles and reports, but to also provide the basic data sets to all interested groups and persons. We believed that the data produced in this project, including in particular, experimental and calculated 3D dose distributions inside the phantom, are potentially of great value for space radiation scientists world-wide. Therefore, the free and convenient access to numerical, tabulated results of HAMLET is one of the main responsibilities of this project.
HAMLET WEBPAGE
Apart from the scientists the other important audience is the general public. The presentation of scientific data to the public is strongly emphasized within the project. The Public Outreach of HAMLET was optimized by installation of the HAMLET web page under
http://www.fp7-hamlet.eu with the following content:
* Introduction to the HAMLET project - including updates of project schedule
* The space radiation environment
* Human presence in space and the risks due to radiation
* Space radiation measurements
* Phantom experiments in space
* MATROSHKA Experiment - Timeline, Documentation
* MATROSHKA Experiment - Scientific Data
* MATROSHKA Experiment - 3 D Dose Distribution Model
* Literature database
* Download Section
* Public Outreach Section
The scope of this page is not only to inform the public about the project itself, but rather provide a comprehensive but concise overview of the space radiation environment, detector instrumentation, radiation transport models and associated topics, and highlight the expertise of the participating institutions. An image gallery serves as an online repository of digital images pertaining to the MATROSHKA experiment and HAMLET activities.
(See: Figure MAIN-1: HAMLET Webpage)
HAMLET Public Outreach Events
The HAMLET consortium held five dedicated HAMLET Public Outreach (PO) Events within the timeframe of the HAMLET project, hosted and organized at the bases of the participating institutions, to further increase the awareness of the public audience to the significance of radiation exposure for the future development of human spaceflight.
The intention of these 'Public Outreach Events' was the presentation of the 'science background', the 'current state of research' and the 'further planned activities' of the group to a scientific interested public audience as also given in the overall topics:
* Human Space Exploration
* Hazards from Space Radiation
* How Do We Measure Space Radiation?
* The Matroshka Project
* From Apollo to the ISS
* To Moon, Mars and Beyond ...
The HAMLET project partners gave talks about the baselines of radiation protection in space, the risks of long-duration space flight to humans, the scientific reason behind the MATROSHKA experiment, and the current status of the HAMLET project. This was accompanied with 'hands-on experience' for the general public to space radiation hardware, e.g. a training model of the MATROSHKA phantom.
The 1st HAMLET Public Outreach (PO) Event was held on 1-2 April 2009 at Vienna University of Technology, Vienna, Austria. The keynote lecture on radiation risk in human spaceflight was given by Prof. em. Dr. Jürgen Kiefer, from 1970 to 2002 Professor of Biophysics at Justus Liebig University Giessen, Germany. The event was acknowledged also by the Vienna City Council for Cultural Affairs and Science Policies and included a space:?rt Exhibition that attracted considerable audience. The 2nd HAMLET PO Event was held on 21 January 2010 at St. Catherine's College in Oxford, organized by HAMLET partner HPA followed by the 3rd HAMLET Public Outreach at the 12 October 2010 organized by HAMLET partner AERI at the Budapest University of Technology, Hungary. The 4th Public Outreach Event organized by HAMLET project partner IFJ was held on the 05th April 2011 at the Polish Academy of Arts and Science, Krakow, Poland. HAMLET partner DLR organized the 5th HAMLET Public Outreach event at the 15. September 2011 at the Bonn-Rhine-Sieg University of Applied Sciences, Campus Rheinbach in Rheinbach, Germany in the frame of the Annual Meeting of the German Radiation Research Society. The events attracted attendees with scientific and academic background but also students and an interested public audience. The HAMLET PO Events were advertised trough press releases, magazine articles, leaflets and posters. In addition TV and radio interviews documented the public interest.
(See: Figure MAIN-2: PO-1 Vienna)
(See: Figure MAIN-3: PO-2 Oxford)
(See: Figure MAIN-4: PO-3 Budapest)
(See: Figure MAIN-5: PO-4 Krakow)
(See: Figure MAIN-6: PO-5 Rheinbach)
HAMLET Science achievements
The science achievements of the HAMLET project are disseminated publicly through a web database. Following the definition of a unified structure for the experimental data provided by the individual participants, a front end of the web database has been designed which allows for convenient and reliable uploading of the processed dosimetric data under
http://www.fp7-hamlet.eu/index.php/database. The data archive currently contains absorbed dose rates measured under extravehicular activity (EVA) conditions during the MTR-1 experiment by miniature luminescence detectors at about 4,800 sites within the anthropomorphic phantom body. The user is graphically assisted in navigating through the torso. The data archive will be expanded in the future with data from the MTR-2A and MTR-2B experiment phases, as well as with the data from the active radiation detectors upon publication of these results in scientific journals.
HAMLET Exploitation of results
Besides the web-based activities, the participants aimed for publishing in high rated scientific journals - and presenting summaries of the output of their work to the scientific community at relevant international conferences and workshops. As an example the presentations were aimed for interdisciplinary international conferences as the biannual Committee on Space Research (COSPAR), the annual International Astronautical Federation (IAF), as well as for meetings directly related to space radiation research, as the annual International Workshop for Space Radiation Monitoring (WRMISS) http://www.wrmiss.org organized by Guenther Reitz (DLR). Presentations at the mentioned meetings increased the public awareness as well as initiate discussions within the scientific community.
Dissemination Plan after HAMLET
The dissemination of results gathered within the HAMLET project will not stop after the end of HAMLET. The intention of the project partners is the following:
HAMLET Webpage: The HAMLET webpage will be kept online under http://www.fp7-hamlet.eu for the upcoming years with updates related to the MATROSHKA project and the work still performed by the project partners. This update of the webpage will also include the update of the Literature database which was set up in the frame of Work Package 3 of HAMLET.
HAMLET Database: The database for the science data generated within HAMLET - both for the passive radiation detectors, as well as for the active radiation detectors - will be kept online as part of the HAMLET webpage and populated upon final publication of the scientific data gathered within the HAMLET project by the project partners.
HAMLET Publications and Presentations: A vast amount of data has been analysed and compared and put into perspective within the three years of the project lifetime. This data was not only limited to the data evaluation performed for the MATROSHKA space experiments, but also focused on the ground based intercalibration of radiation detector purposes and submitted as part of the deliverables and milestones of the HAMLET project. The main aim of the HAMLET project partners for the upcoming time to come will be the final presentation and publication in peer reviewed journals of the outcome of the HAMLET project.
Impact
The HAMLET consortium aimed to advance the current knowledge by focussing and connecting the leading European scientists in space radiation dosimetry, to explore and exploit the vast amount of data gathered within the European MATROSHKA project, thereby:
* Developing tools to archive, access and process data obtained from different sources
* Mobilising the best expertise for the analysis and interpretation of space data, selecting the most innovative and challenging objectives in emerging scientific fields
* Promoting the contribution of space assets to the scientific and technological knowledge and foster its transfer to educational bodies
The development of tools to archive and analyse raw and processed data was one of the main goals of the HAMLET project. By providing the investigators with a common tool, in the form of a web-based infrastructure, they were able to upload their individual data sets, and bring these data sets in alignment with data sets from the other participants, therefore enabling the integration and full exploitation of the data.
The HAMLET consortium brought together the leading European scientists in space dosimetry, for radiation monitoring using both active and passive detectors, for theoretical calculations of the radiation environment in space, and for the assessment of doses to personnel inside and outside of space vehicles. This comprehensive expertise in the different methods of radiation detection and calculation lead to a unique data set now available to the scientific community.
After the accomplishment of the work, Europe has now acquired an added exceptional scientific value, which up to now, did not exist world-wide. This knowledge will not only be disseminated in the scientific community, but will also kept as an open source and brought to the public audience. A result of the the HAMLET project already fostered the cooperation with GSI, Darmstadt, Germany and NIRS, Chiba, Japan in the field of radiation protection and cancer research.
DLR provided GSI, Darmstadt, Germany an MATROSHKA phantom for the usage as „patient" in the frame of the FP7 ALLEGRO project aiming for the determination of the out of field radiation doses received during cancer treatment and the comparison of different treatment modalities (IMRT, Proton and Carbon beams). DLR provided radiation detectors and its expertise for their evaluation within this project.
Irradiations have been performed at:
* Klinikum Goethe University (KGU) in Frankfurt, Germany, IMRT (Intensity Modulated Radiation Therapy) photons;
* Svedberg Laboratory (TSL) in Uppsala,Sweden, (Passively modulated protons)
* Paul Scherrer Institute (PSI) in Villigen, Switzerland (Scanned protons)
* National Institute of Radiological Sciences NIRS (HIMAC), Chiba, Japan, (Passively modulated carbon ions)
* Helmholtzzentrum für Schwerionenforschung GmbH (GSI) in Darmstadt, Germany, (Scanned carbon ions)
The outcome of this cooperation was submitted in two papers to the Journal „Radiotherapy and Oncology" at the end of September 2011.
Further on the results of the HAMLET project are considered as input by the International Commission on Radiological Protection (ICRP) Task Group 67 "Radiological Protection in Space" for the description of radiation fields and doses inside the human body as part of its report titled "Assessment of Radiation Exposure of Astronauts in Space". This will constitute the first international regulation in how to assess the radiation exposure of Astronauts. A further step will be, based on this ICRP report, a new international report on risk assessment of space radiation.
List of Websites:
http://www.fp7-hamlet.eu
http://www.fp7-hamlet.de
http://www.fp7-hamlet.at
http://www.fp7-hamlet.se
http://www.fp7-hamlet.hu
http://www.fp7-hamlet.org.uk
