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The assessment of human exposure from natural, medical and occupational exposure and the associated risks

Objective

The overall aim of the project is to develop reliable methods to measure the spectral and angular distribution of external radiation in the workplace and to use the results to estimate effective dose equivalent.
The technique for the measurement of energy spectra and directional distribution of photon fields has been reviewed and equipment changes made to reduce the risk of contamination in the workplace and increase the speed of measurement. Preliminary results have been obtained on the feasibility of using sodium iodine detectors, involving the use of special filters so that they can provide spectral and dose rate information at the same time. Installation of suitable collimation, so that directional information can also be obtained, is under investigation.

Work has started on the EGSA Monte Carlo computer code to determine theoretically the response of photon detection systems as a function of energy and angle. Work has been carried out to install the code onto personal computers and to validate its operation.

Operational improvements have been made on the neutron spectrometry system to reduce the time required to produce neutron spectra from raw data. A new version of the MCNP Monte Carlo code has been written that transports electronics besides neutrons and photons, incorporating the EG54 electron modules.

A tissue equivalent ion cyclotron resonance unit (ICRU) sphere is being used to determine backscatter factors with different X-ray beams from the ISO catalogue in roder to validate MCNP-E in this range of energies. Preliminary calculations have been performed in the kerma approximation in order to determine backscatter factors, mean energy and energy spectrum of the backscattered radiation on the axis of the beam frontally of the ICRU sphere for ISO narrow spectrum series and BIPM series ranging from 10 kV to 300 kV.

In roder to take into account the most recent trends of the ICRU the previous program has to be modified and a revised program is now under consideration.

An extensive review of the literature relating to particle clearance from the human respiratory tract was carried out. Draft documents were completed on: justification of the approach and assumptions in the proposed clearance model; particle clearance from the extrathoracic airways; partical retention in the thoracic lymph nodes. The results were used to select reference values for the proposed compartment model to describe particle clearance from the human respiratory tract.

The model proposed is intended for both dosimetry and bioassay. Target cells have been identified in each respiratory tract region, and the doses to these have to be evaluated, rather than simply the mean lung dose. A microcomputer program, LUDEP, has been developed to calculate doses to each region of the respiratory tract, doses to all other specified body organs, and excretion rates and retention curves. Test calculations were made. For example, for a 1 um AMAD aerosol of a long lived alpha emitter such as plutonium-239 in oxide or nitrate form, it was found that the main contribution to the effective dose from irradiation of the respiratory tract arises from the dose to the bronchial epithelium.

Comparison of the National Radiological Protection Board (NPRB) compendium of dose per unit intake values with data from the Bundesant fuer Strahlenschutz (BFS) has been undertaken. Agreement was very good for adults (97% of nuclides agreeing to within 10%), and slightly poorer for children.

The implications of the draft recommendations of the ICRP on internal dosimetry have been examined. The low weighting factor for bone surfaces allows an excessive dose per year from certain nuclides. Suggestions are made to remedy this, although it may not be relevant to practical situations.

An electronically controlled servopump for dispersion experiments in models of airways has been constructed, to study regional deposition in the human respiratory tract. The effect on particle dispersion of holding the breath for up to 1 minute has been investigated.

A method has been developed to produce submicron monodisperse radioactive particles at a sufficiently high concentration for measurements of clearance and regional deposition in humans.

The retention of radioactive particles deposited from small aerosol boluses in the conducting airways has been measured for different sizes of particles. The slowly cleared portion has been found to decrease from 60% for 1.6 um particles to about 25% for 6 um particles. Estimates of tracheobronchial and alveolar deposition as functions of particle size have been made. Error introduced by assuming the whole tracheobronchial tree to be cleared rapidly in significant, but within the natural biological variation of the data.

An improved spinning top aerosol generator has been constructed to produce spherical iron oxide (Fe 304) particles with a high degree of monodispersity and a high particle number concentration. Using these particles, the intracellular viscosity and the cell activity of lung macrophages have been studied in vivo. The intracellular viscosity has been found to be 65.3 Pa s. The macrophage activity has been characterised as a randomization process with randomization energy of 6.7 E18 J.

The algebraic regional deposition model, based on a statistical analysis of available data, has been extended to make allowance for age and sex, disease, and natural biological varability.

A review of breathing parameters and lung volumes for use in respiratory tract dosimetric models was made. Reference values were recommended for adults and children of several ethnic groups.

A study of the deposition of inhaled particles in the nose of adults suffering from rhinitis was made. Nasal deposition of a polydisperse aerosol of isopropyl myristate was measured in a group of 25 healthy subjects and 24 suffering from infections rhinitis. Anterior rhinomanometry was measured in each subject. Mass deposition was measured by comparing inhaled and expired aerosol concentrations. Nasal depositions of certain masses of particles (in the size range 0.5 to 6 um, 97% of the aerosol) were found to be significantly higher in subjects with rhinitis.

Eight subjects were studied twice, while healthy and while suffering from the disease, and showed clear differences in nasal resistances, pressure drop and aerosol deposition, before and during rhinitis.

An investigation was made of the slow clearance of particles administered by inhalation from the large airways of rats. Fischer-344 rats were exposed to an aerosol of fused aluminosilicate particles labelled with cobalt-57. At 1, 7, 28 and 112 days afar inhalation the animals were killed and the tracheas examined for cobalt-57. A measured length of trachea was defined in situ, then removed and washed repeadally with saline. The region of the first bifurcation was similarly removed and washed. The cobalt-578 content in the washings and the airway wall was determined by scintillation counting.

From 3 days after inhalation, the animals were regularly monitored in a small animal whole body counter, and excretion measurements, of cobalt-57 were made.

The retention of particles in the trachea has been analysed into 3 functional compartments. T1 represents material cleared rapidly, Ts represents slow or stationary material remaining on the surface of the epithelium, and Tur particles sequestered in the airway well. Expressed as fraction of the whole body retention at 1 day after inhalation, multiplied by 1E5 and normalized to a measured tracheal length of 20 mm, T1 decreased from 22 at 7 days to 0.6 after 112 days. Ts was 39 at 7 days and fell to 37 by 28 days and 7.0 by 112 days. Tw remained between 10 and 15 throughout.

The fraction of the inhaled particles estimated to remain stationary or slow moving on the epitherial surface was the largest of the 3 compartments at 7 and 28 days after inhalation, as order of magnitude greater than the rapidly cleared component at 28 and 112 days. It was found that nearly all the cobalt-57 was within macrophages. The study demonstrates that long term retention of particles on the surface of large airways in possible.

About 40 samples of foetal tissues and placentae from abortions at 14 to 19 weeks were obtained. For initial measurements of plutonium-239, combined samples of foetal and placental tissues were analyzed by mass spectrometry. Separate analyses of foetal and placental tissues are now in progress. Measurements of polonium-210, by radiochemistry, have shown concentrations to be about 3 orders of magnitude greater than for plutonium-239, with about 2/3 of the total activity in the placenta.

The transfer of plutonium to the developing embryo and foetus is being studied using rats and guinea pigs. Plutonium-238 was administered to the animals at different stages of pregnancy and transfer to the embryo and foetus determined by autoradiography and tissue analysis. Retention in the total foetoplacental unit (FPU) was similar in the 2 species and increased with advancing gestation. However, distribution of plutonium-238 within the FPU was different, with the yolk sac concentrating the greatest proportion in the rat while the placenta showed greater retention in the guinea pig. Transfer to the embryo or foetus accounted for a small proportion of total FPU activity, with greatest concentrations in early and late gestation and lowest in mid gestation. Preliminary data on the transfer of polunium-210 to the foetus in rats and guinea pigs show that, as far plutonium, the greatest concentrations were in the yolk sac. Concentrations of polonium-210 in the foetus were greater than for plutonium-238 at mid gestation but lower in late gestation.

The animal data have been used to estimate doses to the human foetus from material intakes. For a chronic material intake of plutonium-239 throughout pregnancy taking account of both in utero doses and activity retained by the newborn child, the overall lifetime dose to haemopoietic tissue of the offspring was estimated to be 2 orders of magnitude less than the equivalent material dose.

The rodent foetal gonads have been established as a more sensitive indicator of radiation damage than the foetal brain and levels of irradiation from incorporated radionuclides could be estimated up to 0.37 Gy/day protracted irradiation throughout gestation. The limits of this model are animal survival for the studies of brain histology and germ cell survival for the effect of the gonads. With acute gamma irradiation of 1 Gy on day 15 of gestation, a dose rate effect was observed in brain tissue at dose rates of 23.9 Gy/day and 239 Gy/day but the greatest effect on the testes was observed with 0.87 Gy/day. However, the results obtained after acute irradiation are not applicable to protracted irradiations.

A detailed investigation is underway of the distribution within the human foetus of natural alpha radioactivity using autopsy samples obtained from various stages of foetal development from 18 weeks to stillborn. Where possible samples comprising placenta, cord, liver, spleen, thymus and spine have been obtained. These were loaded against TASTRAK (CR-39) alpha track detector and stored for at least 1 year. The technique allows total alpha activity in a sample as small as 1 gram to be determined with a detection limit of approximately 0.01 Bq/kg. Of 45 cases currently under examination a completed analysis is available for 14 cases.

The alpha activity in the foetoplacental unit appears to be dominated by polonium-210 which is believed largely to be supported by lead-210. Total alpha activity in the placenta is around 0.025 Bq/kg with levels in the liver, spleen and thymus ranging up to 0.05 Bq/kg. Values in the cord appear to be higher at around 0.1 Bq/kg. The highest activities in the foetus are in the spine where values up to 2 Bq/kg with an average of 0.75 Bq/kg are found. The activity in the spine is sufficiently high that it is possible to resolve the level of radium-226 from the total alpha activity present. Here the ratio of total alpha activity to that from radium-226 is around 40 to 1 in comparison with adult bone where the ratio is around 10 to 1. The reasons for this difference could be due to different transplacental transfer factors for radium-226 and lead-210.

The work of mapping radon sources on a large scale have been progressing, with large numbers of measurements of radon in soil gas made and mapped. A method has been developed for transferring data on radon in homes in a given area in a way that preserves the detailed geographical information for correlation with geology without compromising the confidentiality of the radon results.

Measurements have been made of radon levels in new and existing homes with various antiradon measures. About 30 new homes on 3 building sites in a radon affected area are under investigation. The homes all have suspended concrete floors, some incorporating radon preventive measures such as a continuous membrane across the whole floor area and provision for subfloor ventilation. Measurements have shown low radon levels in homes both with and without preventive measures, due to the warm summer. Measurements are continuing through the winter to determine the effectiveness of the preventive measures.

Tests have been carried out in various existing homes and other buildings where radon remedial measures have been installed. In buildings with soild concrete floors, subfloor sumps attached to extract fans have been shown to be effective and durable. Remedial measures on suspended timber floors have proved to be more problematical. Sealing the top surface of the floors has proved to be difficult and disruptive for the householder. The provision of a continuous flow of air across the subfloor space in providing promising results. Underpressuring the space has proved to be less effective in reducing radon levels and more likely to cause problems with dampness. Tests in buildings where the natural underfloor ventilation has been increased by the provision of extra vents have shown this to be unreliable in reducing radon levels.

In order to measure the transport of radon in soil as a function of various soil parameters such as porosity, permeability, grain size distribution, radium content and water content, it was first necessary to design and construct equipment. A cylindrical stainless steel vessel with an inner diameter of 2 m and a height of 2 m was designed. Around the upper metre there is a ring filled with water to close off the air under the lid from the air in the laboratory. In the wall of the vessel are 12 pots for inserting probes. The design of the vessel has been completed and its is now under construction.

A multifunctional probe to measure the radon concentration in the soil gas, the permeability of the soil and the water content of the soil was designed and a prototype constructed. The main problem is the determination of the shape factor of the probe. The shape factor has to be measured to derive values for the soil permeability. For this purpose a perforated box has been designed to be placed near the bottom of the vessel and covering almost the complete cross section of the vessel. The vessel is filled with dry sand through which an airflow is induced via the perforated box. Using this simple geometry the permeability of the sand can be measured without the probes. Afterwards the shape factor can be deduced by measuring the permeability with the probes. In order to select the most suitable type of sand, various samples of commercially available sand are currently being tested for radium content, radon emanation factor, grain size distribution and pF curve.

A set of drilling tools has been made. This includes 4 20 mm coarsie drills with extension rods for depths down to 5 m, and 3 12 mm drills for sampling and for preparation of probe positioning. Also 2 soil samplers, capable of removing 25 cm{3} samplers of soft soil from depths down to 4 m have been made. In addition accessories like a 2.5 m long chisel and a hauling tool have been made. The drills are operated with a hand held electrical machine supplied from a portable generator. Experience with the drilling tools and a borehole casing technique have been gained during the period.

A radon emanation measurement system for small samples (50g) of soil has been assembled and tested. The system is based on scintillation cells with renewable scintillation foils. The air volume of the total system is kept as low as 150 cm{3} in order not to dilute the radon concentration. The results achieved so far indicate that the background count rate, even with fresh scintillation foils, is too high.

A probe for gas permeability measurements in soil has been made. The probe, which has a diameter of 16 mm, is led through the borehole casing tube to the measurement position. A packing procedure designed to prevent gas leaking along the casing has been tested in the laboratory. The necessary field instrument for the permeability probe has been assembled and preliminary laboratory and field measurements have been performed.

Soil gas radon concentrations at a depth of 0.5 m have been measured at a number of potential test site locations at Risoe National Laboratory and an area has been selected, where the test structure is to be established. The soil in the area is mainly moraine clay. This type of soil is typical of a large part of Denmark. In addition, the soil gas radon concentrations have been measured at 6 locations and the permeability at 1 location close to the planned site at depths of 0.5 m to 0.7 m.

Initial modelling efforts have been directed towards the design of the experimental site. Analytical expressions for a linear, cylindrical and spherical geometry have been used for estimating the effective soil gas resistance, the depletion of soil gasradon and the radon entry as functions of the geometrical parameters and soil permeability. A 2-dimensional, finite difference model for studying soil gas transport has been developed. It has been used to examine the influence of a high permeability layer at the interface between soil and test structure. It was found that the incorporation of such a layer would make the experimental situation less sensitive to possible soil inhomogeneities close to the entry point.

The possiblity of using the 3-dimensional finite difference code TRISCO for the evaluation of radon mitigation strategies in dwellings was considered. The domain of validity of the model was delimited and the following main hypotheses were justified:
the radon transport from soil into a dwelling occurs mainly by pressure driven air flow;
the air flow under the slab is assumed to be laminar;
the steady state condition is assumed.
The program calculates the pressure fields under the floor. Because all the details of the configuration can be included in a very simple way and because of the simple and useful graphical outputs, the code appears to be particularly well suited to calculating pressure fields in the soil, therefore allowing practical evaluations of mitigation systems performances.

Measurements have been made in a school with high radon levels and remedial measures recommended. The degree of permeability to air of the studied zone of the building was measured using the pressurization method. The air tightness of the inner walls of the various rooms was also evaluated. Measurements of tracer gas (nitrous oxide injected in the basement) concentrations in different rooms for different experimental conditions were made, as a function of time, together with radon concentration measurements. Conclusions were drawn concerning the radon entry paths and the influence of a number of factors on the measured concentrations and some remedial measures were recommended.

A model was developed to estimate the dose equivalent to the public due to soils and buildings, as a function of various soil and building parameters. The model takes the following radon sources into account:
pressure driven radon transport via the soil into the underfloor space and dwelling;
diffusion of soil gas into the underfloor space successive transport into the dwelling;
exhalation of radon from building material.
To calculate the respect we contributions, the numeric values of a number of input parameters were fed into the model. These parameters relate to:
soil (porosity, emanation factor, radium-226 content);
weather (temperature gradient inside to outside, wind direction and strength);
location (watertable, geometry factors);
building materials (surfaces, thickness, emanation factor);
inhabitants (ventilation, residence time).
The calculation was performed using typical parameter values encountered in the Netherlands and radiation doses were obtained which were in the expected ranges.

Field investigations have been carried out in an area which is underlain by carboniferous rocks ranging from limestones to mudstones and sandstones with intrusions of basic igneous rocks. Uranium concentrations have been identified which could give rise to high radon emanation. Survey methods have involved the measurement of soil gas radon and thoron, gamma spectrometric determinations of bismuth-214, thallium-208 and potassium-40 photopeak intensity in soils and rocks and have included the determination of total uranium and labile radium. Analysis of the data shows that most of the variation in total gamma activity can be attributed to variation in uranium concentration in rocks and soils. Statistical analysis indicates that there is a highly significant difference in the radon values in soil gas, in relation to rock types, so that the geological map provides a useful first indication of radon in soil gas distributions. Repeated traverses covering an area of contrasting geology, land use and rock permeability shows an identity in radon distribution patterns for different seasons. Laboratory studies for the determination of emanation coefficients of soils are underway and data is being compared with studies of carrier gas concentrations already undertaken. A provisional soil gas radon concentration map has been produced. Early data indicate that this provides a good indication of areas in which houses with radon values above the action level may be found.

2 houses have been instrumented for collecting continuous data, which includes environmental temperatures in a variety of locations indoors and outdoors, pressure differences across the building shell in a variety of locations and radon gas concentrations in different indoor and subfloor zones. The data is recorded electronically and hourly averaged data is stored on a computer located in the house. The 2 houses both have indoor radon concentrations which average between 100 Bq/m{3} and 200 Bq/m{3} in the living level and the source of the radon is the soil. The first house, labelled 901, consists of a basement with 2 attached crawlspaces and a single floor living level above the substructure. The second house, labelled 902, consists of a rectangular 2 storied house on top of a small crawlspace on top of the ground.

A radon flow model has been developed which takes as input time varying measured airflows and predicts the time varying radon concentrations in each zone specified indoors. Modelling efforts have been concentrated in 2 areas. The first has been to develop a simple formula for air infiltration into a dwelling which calculates the air infiltrating from the soil gas separately from the air infiltrating from the outdoor air. Also, the mechanisms driving air inflitration are limited to temperature differences between the indoors and the outdoors and to wind and these mechanisms are treated as separately as possible. The second effort has been to develop a procedure for calculating airflows between zones for use in the radon flow model. Some preliminary tracer gas measurements in house 901 have been completed, to give total infiltration into different zones but not interzone flows.

A hydroxypyridone derivative of desferrioxamine (DFO-HOPO), diethylenetriamine pentaacetic acid (DPTA) and a dihydroxamic derivative of DTPA (DTPA-DX) were tested at dosages of 30 umol/kg for their ability to remove plutonium-238 and americium-241 from rats after their intravenous injection as citrate or inhalation as nitrate. The 2 siderophore analogues were provided free of charge by Professor K Raymond, Department of Chemistry, University of California, Berkeley.
The most effective treatment regimen for onjected plutonium-238 was the repeated administration of DFO-HOPO. After 7 days the body content was reduced to 8% of that in untreated animals; the value after DTPA treatment was 15%. Repeated dosages of 3 umol/kg DFO-HOPO were as effective as those of 30 umol/kg DTPA. After inhalation of plutonium-238, repeated treatment with DTPA, DTPA-DX or DFO-HOPO reduced the body content and day 7 to, respectively, 10, 15 and 31% of controls. After inhalation of americium-241 DTPA-DX and DTPA were equally effective, the body content being reduced to 7% of control values with repeated treatment. Injection of DFO-HOPO was ineffective for enhancing the elimination of inhaled or injected americium-241. These results support the strategy of examining the use of siderophore analogues for the decorporation plutonium and americium. However, at present, DTPA should remain the agent of choice, particularly after inhalation.

The efficacy of calcium DTPA and zinc DTPA have been evaluated for removing thorium from the rat after its deposition as nitrate in the lungs. When the initial mass concentration in the lungs simulated human exposure to 4 times the average life intake (ALI) for thorium-232, the prompt (300 or 1000 umol/kg body weight at 30 min) or repeated (30 or 300 umol/kg body weight at 30 min, 6 h, 1, 2, 3 day) administration of calcium DTPA was at best only moderatly successful forenhancing the elimination of thorium-232. By day 7 after exposure, the body content was res pectively 74%, 65%, 90% and 74% of that present in untreated animals. When the mass concentration in the lungs simulated acute exposure to 1.7E-3 times the ALI for thorium-232, the efficacy of treatment was not increased appreciably despite the substantial reduction in mass. After the repeated administration of calcium DTPA at dosages of 30 and 300 umol/kg using the protocol above, the body content of thorium by day 7 was respectively 69% and 51% of that in untreated animals. Under comparable conditions, the efficacy of zinc DTPA was less than calcium DTPA.
The results of these experiments suggest that more effective chelating agents are needed for the treatment of workers overexposed to water soluble thorium compounds.

In the past decade, several phenolic compounds have been investigated in animals for their ability to prevent fatal uranium poisoning. The most promising derivative appears to be sodium 4,5-dihydroxybenzene-1,3-disulphonate (Tiron). In experiments conducted at National Radiological Protection Board (NRPB), the compound was administered to rats in dosages of 30, 300 or 1000 umol/kg at 20, 60 and 180 min after the intratracheal instillation of uranyl nitrate. The amounts of uranium deposited in the lungs of rats were equivalent to intakes by workers of about 12 times the permitted daily limit of 2.5 mg. The average body content of uranium 5 days after exposure, using the treatment regimens above, was respectivly about 100%, 78% and 65% of that in untreated animals.
These results suggest that the administration of Tiron is of limited practical value for enhancing the elimination of uranium from the bodies of overexposed workers.

This investigation concerns:
the efficacy of the siderophore analogues code named DFO-HOPO (a hydroxypyridone derivative of desferriozamine) and DTPA-DX (a dihydroxamic derivative of diethylenetriamine pentaacetic acid) for enhancing the removal of plutonium and americium from the body of the rat after intravenous injection of the actinides; and the study of the reduction of bone tumour risk in plutonium-239 treated rats through the near lifetime administration of zinc diethylenetriamine pentaacetic acid (zinc DTPA) in drinking water.

The study of the effects of continous oral zinc DTPA on bone tumour induction in male Sprague-Dawley rats injected with 37 kBq plutonium-239/kg body weight was completed when the last rat died. Preliminary analysis of the results indicates that treatment with 10E-3 M zinc DTPA as drinking water, beginning 4 days after plutonium-239 injection, reduced the bone tumour incidence from 3.75 + or - 2.0% to 15.0 + or - 2.5%. When the start of treatment was delayed until 30 days post plutonium-239 injection the tumour incidence was reduced only marginally but the survival time to death with a bone tumour was increased by about 17% as compared to untreated rats.

The effects of the 2 new chelators, DFO-HOPO and DTPA-DZ, were compared with that of DTPA in male Sprague-Dawley rats following a single intravenous injection of plutonium-238 and americium-241. Following subcutaneous injection of 30 umoles/kg at 1 hour after radionuclide injection, DFO-HOPO reduced plutonium retention in skeleton and liver, at 7 days postradionuclide injection, to 19% and 6%, respectively, of that in untreated animals. Similar treatment with calcium DTPA was less effective, reducing the skeletal retention to 39% and that in liver to 25% of that found in the untreated controls. DFO-HOPO had no effect on the retention of americium-241. The combination of DFO-HOPO with calcium DTPA was even more effective than DFO-HOPO alone in reducing retention in skeleton and li ver. DFO-HOPO given orally at a dose of 100 umoles/kg 3 minutes after the nuclides was as effective as the injected substance in reducing retention of plutonium-238 in the skeleton and liver.
DTPA-DX, following either subcutaneous injection or oral administration, was less effective than calcium DTPA in removing plutonium from the skeleton and liver, or americium from the skeleton. Injected DTPA-DX did reduce the liver retention of americium by a factor of about 3 compared to calcium DTPA.
The effectiveness of DFO-HOPO was found to decrease exponentially with time after plutonium-238 injection, the approximate half-times for the mobilization of the nuclide from skeleton and liver were 6 and 12 hours, respectivley. Within the dose range 0.3 to 10 umoles/kg, a negative linear relationship was observed when the mobilizing effect was plotted against the logarithm of the injected dose of chelator.

Continous chelate infusion, for 14 days aftr radionuclide injection, was achieved by means of implanted mini-pumps. In general, tissue retention was reduced to a greater extent than by the single injections of the chelators. However, with DFO-HOPO the continous infusion was no more effective than the single injection for mobilizing plutonium from skeleton and liver.

This work concerns the investigation of the efficacy of the siderophore analog 3, 4, 3-LIHOPO (containing 4 hydroxypyridinone groups) in comparison to diethylenetriamine pentaacetic acid (DTPA) for enhancing the decorporation of plutonium-238 as a tributylphosphate complex (plutonium-238 TBP) after inhalation in Sprague Dawley rats.
The first purified sample of 3,4,3-LIHOPO (50 mg) was tested by intravenous injections in rats previously exposed to an aerosol plutonium-238 TBP. 3 groups of rats were used: group 1, 5 rats exposed to plutonium-238 TBP as untreated control animals;groups 2 and 3 exposed to plutonium-238 and injected respectively by DTPA and 3,4,3-LIHOPO. The average initial lung burden was about 3.7 kBq (5.7 ng plutonium). Unique intravenous injection of the different chelates was performed 1 hour after the end of inhalation at a concentration of 30 umole/kg. The rats were killed 7 and 14 days after contamination and lungs, livers, kidneys and femurs collected. The different organs will be counted, results are not yet available.

This investgation concerns the study of the effect of haematopoietic growth factors o
At present, techniques for measuring neutron spectra in the workplace are well developed and measurements will be made at various nuclear installations. For photons, NRPB has designed a simple method to obtain spectral and angular information using Geiger-Muller detectors. Alternative methods of obtaining such information will be investigated, using sodium iodide and germanium detectors.

These devices will be used for measurements in the workplace, and calculational methods will be developed to use these measurements to estimate effective dose equivalent from external photon radiations. Calculations and experimental measurements will be extended to other irradiation geometries for the evaluation of the response of personal dosemeters. The implications of such measurements for personal dosimetry will be investigated and the relationship between operational dose equivalent quantities and effective dose equivalent will be evaluated.

NRPB will coordinate this project, which deals with methods of measurement of the spectral and angular distribution of external radiations in the workplace and draws on experimental investigations and photon transport calculations by the Monte Carlo method. It will provide the expertise and facilities to develop reliable methods for measuring the spectral and spatial distributions. The implications of such measurements for personal dosimetry will be considered, including their utility in making estimates of worker doses.

In collaboration with the UKAEA, ENEA and CEA, NRPB will evaluate various methods to obtain spectral and angular information on external radiations and examine ways in which the data obtained can be used to estimate effective dose equivalent. The NRPB secondary standard calibration laboratory will be used to test various measurement techniques before they are used in the workplace. At present, the techniques for measuring neutron radiation spectra in the workplace are relatively well developed, so efforts will be concentrated on evaluating methods to measure the spatial and spectral distributions of photon radiations. Furthermore, the feasibility of obtaining useful spectral information for beta radiation in the workplace will be investigated.

Funding Scheme

CSC - Cost-sharing contracts
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Coordinator

NATIONAL RADIOLOGICAL PROTECTION BOARD (NRPB)
Address
Chilton
OX11 0RQ Didcot
United Kingdom