Comparison of measurements with active and passive Bonner sphere spectrometers

Because of its high biological efficiency, neutron radiation can be a serious source-and not only around accelerators and nuclear fusion reactors. Roughly half of the radiation exposure of aircrew members is caused by cosmic ray-induced neutrons in a wide energy range. Therefore, following the International Commission on Radiological Protection's recommendations, aircrew are treated as occupationally exposed workers by a recent directive of the European Council, which implies various safety precautions including the dosimetric surveillance. The accurate assessment of operational and limiting quantities such as ambient dose equivalent H*(10) and effective dose E requires the knowledge of the neutron energy spectrum. The CERN-CEC neutron reference field has been designed to resemble the neutron spectrum at an average subsonic aviation altitude. Therefore, it provides an excellent calibration facility for all instruments with intended applications in this field. The stray radiation field is created by a mixed beam of charged hadrons with momenta of 120 GeV/c (about 2/3 protons and 1/3 pions) incident on a cylindrical copper target (50 cm length, 7 cm diam), which is located either under a 40- cm-thick iron shielding or under a 80-cm-thick concrete shielding. The beam monitoring is provided by a precision ionization chamber (PIG) with one PIC count corresponding to ~2.2*10/sup 4/ primary particles. The radiation field can be simulated to a good level of detail by the Monte Carlo code FLUKA. (5 refs).