THE MEASUREMENT USING PASSIVE DOSIMETERS OF THE NEUTRON COMPONENT OF AIRCRAFT CREW DOSE

The cosmic radiation field at aviation altitudes can be measured with simple passive detectors. The non-neutron component may be measured by means of thermoluminescence dosimetry or other techniques, and the ne utron component may be measured using poly allyl diglycol carbonate (P ADC) dosemeters as described in this paper. Effective dose from neutro n radiation becomes the larger component for altitudes above about 10 km, in general. The dominance is more pronounced for higher latitudes. The neutron energies range up to the maximum of the incident protons, that is many GeV. However the majority of the dose is contributed by neutrons of a few hundred MeV and less, with two maxima in the fluence spectrum, one between 1 and 10 MeV and the other between 50 and 150 M eV. We have used PADC dosemeters, electrochemically etched, to estimat e the neutron component of effective dose. Up to 50 dosemeters are use d in a single measurement to obtain an estimate of sufficient precisio n for total neutron effective doses of 50 mu Sv and less. The neutron fluence response characteristics of the dosemeter have been measured u p to 70 MeV. These are extrapolated up to 180 MeV. This extrapolation is validated, partially, by a comparison of measured and predicted rea dings in the CERN reference field. From the dosemeter readings for exp osure on board aircraft, neutron fluence may be estimated assuming an isotropic radiation field and the estimated neutron fluence spectrum. The neutron fluence may then be converted to effective dose using publ ished values of conversion coefficients with the same assumptions of i sotropy and known fluence spectrum. For the measurement results report ed here, the calculated spectrum for the CERN concrete shielded field is used.