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The survey of aircrew exposure required the characterisation and/or the development of a diverse array of both passive and active instruments, which were not available at any one laboratory. To ensure the availability of the most advanced dosimetric systems and the relevant calibration facilities needed for the survey, an international collaboration was formed, which was facilitated by multinational research contracts promoted by the Commission of the European Communities. Close cooperation among scientists with long-term experience in different disciplines, such as cosmic ray measurement in space and radiation protection dosimetry, made it possible to exploit successfully damage track detectors for the accurate evaluation of very low fluences of particles with high energy and high charges. For a long time, the major concern for the assessment of aircrew exposure has been the accurate evaluation of the cosmic ray neutron dose. In this paper, four different dosimetric systems are considered, the response of which is sensitive to both low and high energy neutrons. All these dosimetric systems have provided consistent results when exposed together to the high energy beam facility at CERN, which is considered to approximate the cosmic ray field.

The Italian survey of aircrew exposure has been carried out with different advanced dosimetric systems, as described in part I of this paper. The key strategy of the survey was to obtain on-board comparison of measurements for both passive and real-time detectors flown together with passengers. The survey has been carried out in the period of solar minimum (1995-1997), in which the exposure to galactic cosmic rays reaches its maximum value. Even though carrying out the survey in the period of solar minimum was entirely coincidental, this circumstance has been used to good advantage to obtain a comprehensive set of data of the galactic cosmic radiation with little or no disturbance by the solar activity modulation. This comprehensive set of data covers flight routes between -20 degrees and 75 degrees geographic latitude at different civil aviation altitudes. The survey obtained with different advanced dosimetric systems has been supplemented by a large variety of data gathered with passive stacks on different short-range and long-range flights at supersonic and subsonic altitudes. Some of the most important conclusions which can be drawn from the survey are: (i) aircrew of civil aviation receive annual doses within the range of 1 mSv to 6 mSv; (ii) data from different periods of solar minimum agree well, since the discrepancies encountered seem mainly due to the different dosimetric systems used; (iii) repeated measurements on the same route are highly consistent.

The radiation fields on board aircraft are quite complex and cover an energy range that is unusual in ordinary radiation protection work. Usually dosemeters measure only one radiation quality and the mixture found on board makes measurements complicated. There is also some doubt when it comes to the best choice of quantity for this application and no radiation standards exist for this kind of radiation field. For those reasons there is a need to find a standard measurement procedure that could serve as a reference for other, maybe simpler, measurements or for calculations of route doses. The only direct reading dosemeter that both measures the absorbed dose to tissue and the radiation quality (in terms of lineal energy) is the tissue-equivalent proportional counter (TEPC). The instrument was originally developed for scientific purposes and is still used as such. The detector consists of a gas filled cavity surrounded by a few mm thick wall. Both wall and gas consists of tissue-like material. The measurement principles are explained. Results observed with TEPC instruments are demonstrated. A preliminary collection of data reported by different groups from measurements on board aircraft will be shown. The results agree within +/- 20%. The conclusion is that TEPC instruments have the capacity of serving as reference instruments.