As a result of the recent recommendations of the ICRP 60, and in anticipation of possible regulation on occupational exposure of Canadian-based aircrew, an extensive study was carried out by the Royal Military College of Canada over a one-year period to measure the cosmic radiation at commercial jet altitudes. A tissue-equivalent proportional counter was used to measure the ambient total dose equivalent rate on 62 flight routes, resulting in over 20,000 data points at one-minute intervals at various altitudes and geomagnetic latitudes (i.e. which span the full cut-off rigidity of the Earth's magnetic field). These data were then compared to similar experimental work at the Physikalisch Technische Bundesanstalt, using a different suite of equipment, to measure separately the low and high linear energy transfer components of the mixed radiation field, and to predictions with the LUIN transport code. All experimental and theoretical results were in excellent agreement. From these data, a semiempirical model was developed to allow for the interpolation of the dose rate for any global position, altitude and date (i.e. heliocentric potential). Through integration of the dose rate function over a great circle flight path, a computer code was developed to provide an estimate of the total dose equivalent on any route worldwide at any period in the solar cycle.

The assessment of the exposure to cosmic radiation onboard aircraft is one of the preoccupations of bodies responsible for radiation protection. Cosmic particle flux is significantly higher onboard aircraft than at ground level and its intensity depends on the solar activity. The dose is usually estimated using codes validated by the experimental data. In this paper, a comparison of various codes is presented, some of them are used routinely, to assess the dose received by the aircraft crew caused by the galactic cosmic radiation. Results are provided for periods close to solar maximum and minimum and for selected flights covering major commercial routes in the world. The overall agreement between the codes, particularly for those routinely used for aircraft crew dosimetry, was better than + + + + +20 % from the median in all but two cases. The agreement within the codes is considered to be fully satisfactory for radiation protection purposes.

An on-going investigation using a tissue-equivalent proportional counter (TEPC) has been carried out to measure the ambient dose equivalent rate of the cosmic radiation exposure of aircrew during a solar cycle. A semi-empirical model has been derived from these data to allow for the interpolation of the dose rate for any global position. The model has been extended to an altitude of up to 32 km with further measurements made on board aircraft and several balloon flights. The effects of changing solar modulation during the solar cycle are characterised by correlating the dose rate data to different solar potential models. Through integration of the dose-rate function over a great circle flight path or between given waypoints, a Predictive Code for Aircrew Radiation Exposure (PCAIRE) has been further developed for estimation of the route dose from galactic cosmic radiation exposure. This estimate is provided in units of ambient dose equivalent as well as effective dose, based on E/H x (10) scaling functions as determined from transport code calculations with LUIN and FLUKA. This experimentally based treatment has also been compared with the CARI-6 and EPCARD codes that are derived solely from theoretical transport calculations. Using TEPC measurements taken aboard the International Space Station, ground based neutron monitoring, GOES satellite data and transport code analysis, an empirical model has been further proposed for estimation of aircrew exposure during solar particle events. This model has been compared to results obtained during recent solar flare events.

As a result of the recent recommendations of ICRP 60 and in anticipation of possible regulation on occupational exposure of commercial aircrew, a two-part investigation was carried out over a one-year period to determine the total dose equivalent on representative Canadian-based flight routes. As part of the study, a dedicated scientific measurement flight (using both a conventional suite of powered detectors and passive dosimetry) was used to characterise the complex mixed radiation field and to intercompare the various instrumentation. In the other part of the study, volunteer aircrew carried (passive) neutron bubble detectors during their routine flight duties. From these measurements, the total dose equivalent was derived for a given route with a knowledge of the neutron fraction as determined from the scientific flight and computer code (CARI-LF) calculations. This investigation has yielded an extensive database of over 3100 measurements providing the total dose equivalent for 385 different routes. By folding in flight frequency information and the accumulated flight hours, the annual occupational exposures of 26 flight crew have also been determined. This study has indicated that most Canadian-based domestic and international aircrew will exceed the proposed annual ICRP 60 public limit of 1 mSv.y-1, but will he well below the occupational limit of 20 mSv.y-1.

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