Different systems of detectors for the measurement of high and low energy neutrons were set up and calibrated. As a result of this work, it was concluded that a passive multidetector stack would provide a simple method for measurement of the different components of the radiation field experienced at aviation altitudes. This had the advantage that it would provide average exposure data if left on an aircraft over an extended period of time.
The study of HZE particles in the radiation flux at aviation altitudes was carried out using track etch detectors, which were incorporated into the multidetector package. The track etch detectors were utilised on flights carried out at a number of different altitudes and have confirmed the presence of particles with Z values up to and including magnesium (Z = 12) at the highest altitudes relevant to civil aviation.
The main objectives in respect of active instrumentation were the use of the extended rem counter (LINUS) at aviation altitudes and the development of the HANDI (Homburg Area Neutron Dosimeter). Calibration and testing of both these instruments has proceeded in accordance with the plans set out in the proposal.
The most successful source of new in-flight measurements using active instrumentation provided measurements on some 20 return commercial flights to various destinations during the course of the Contract.
Differences in the results obtained using the LUIN and FLUKA codes were studied and it was generally found that the latter predicted higher fluxes. Discrepancies remain between expected and observed results and it is concluded that the LUIN code needs improvement with respect to the neutron contribution to dose.
The calculation of dosimetric quantities concludes that ambient dose equivalent is a conservative estimate of the quantities effective dose and effective dose equivalent for the fields encountered at aviation altitudes.
Contract Project 6 was primarily concerned with the establishment of reference radiation fields at the high energy proton accelerator facility at CERN. These reference fields proved to be most valuable in enabling comparisons to be made of the instruments used by the various Contractors. One of the most important results established using these experimental fields was that the dose limit of 2 mSv recommended in IRCP 60 at the surface of the abdomen for a pregnant woman does not assure a dose limit to the foetus of 1 mSv.
The results obtained within this Contract confirm the view that air crew normally employed on medium and long haul flight duties are likely to receive doses in excess of the annual dose limit of 1mSv for members of the public. This conclusion implies that such workers fall within the classification of Category B radiation workers and requires that an assessment of their doses should be made. Project 1 considers a number of options for assessing the dose and concludes that a route dose can be allocated for each flight, the total of such doses providing a satisfactory estimate of total dose in compliance with the European Radiation protection Directive.
In the case of pregnant female air crew, the possibility exists that continuing flight duties for the first trimester of pregnancy could result in exceeding the relevant dose limit. This must not be permitted to occur and appropriate legislative steps will need to be considered in the near future to obviate the possibility. The results obtained within the Contract suggest that normal flight duties with the aviation industry should not result in any air crew falling into the Category A for radiation workers. It is therefore not likely that elaborate procedures require to be introduced for minimisation of doses.
DETECTION AND DOSIMETRY OF NEUTRONS AND CHARGED PARTICLES AT AVIATION ALTITUDES IN THE EARTH'S ATMOSPHERE
The objectives of this proposal are to improve and adapt existing types of instrumentation for the measurement of neutron and cosmic ray particle flux at altitudes used in aviation. The instruments will be calibrated as a multidetector system for the appropriate energy ranges and species of particles in suitably equipped laboratories. They will then be flown in aircraft at altitudes and latitudes in normal use for aviation purposes. This should enable the measurement of the flux of the high energy neutron component of cosmic radiation and of the charged particles which penetrate through the upper layers of the atmosphere. The neutron component will be measured by track counting in mylar films of fissions induced in sheets of bismuth, gold and other materials. Solid state nuclear track detectors will be used to register and identify the charged particles. A modified Anderson-Braun counter will be used for the determination of dose rates due to neutrons up to 400 Mev. Determination 0E the organ response functions and modelling based on the measurements should enable predictions to be made of the dose associated With various patterns of travel involved Eor flight crew employed in civil aviation.
Funding SchemeCSC - Cost-sharing contracts