Global Measurements of the Radiation Exposure of Civil Air Crews from 1997 to 1999

Abstract

The exposure of aircrew to the increased cosmic radiation at aviation flight altitudes will soon be treated in the European Union as an occupational risk, with the consequence that the radiation exposure of aircrew must be determined. This work describes about 200 h of in-flight measurements performed during a period of 22 months from 1997 to 1999 on cargo aircraft. Various monitors were used to measure different radiation field components and to investigate the spatial dose equivalent rate distribution and the spatial radiation field composition. The monitors were rem counters for neutrons, and a scintillator and an ionisation chamber for the directly ionising and photon components. One of the main goals was to calibrate the monitors in the cosmic radiation field at flight altitudes against a tissue-equivalent proportional counter (TEPC) used as a reference instrument for the quantity ambient dose equivalent. The sum of the readings of a neutron rem counter with its response extended to high energy neutrons and of an ionisation chamber was found to be a fair approximation of the total dose equivalent as measured by the TEPC. The 'field calibration factor' determined is 1.0 ± 0.1. The global dose equivalent distributions as a function of magnetic latitude and cut-off rigidity were obtained for the range of altitudes encountered in civil aviation and can be described by simple mathematical functions for use in rough dose-equivalent rate estimates. Surrounding the TEPC with an active shielding detector and the application of coincidence techniques allowed dose equivalent fractions of charged and uncharged particles in the cosmic radiation to be separated. The low-LET radiation component was found to consist of 90% charged particles and 10% photons while the high-LET component contains a fraction of 30% from protons (pions) and 70% from neutrons.