Dose-Equivalent Rate from Cosmic Ray Neutrons

Abstract

On the basis of published data from cosmic ray studies, the dose-equivalent rate due to naturally occurring neutron radiation is calculated to be 11.8 ± 1.0 mrem/yr for a small piece of tissue in air at sea-level and at a location with geographical coordinates (lat. 55°2′N, long. 3°21′W). It is deduced that the neutron dose-equivalent experienced by the population at sea-level for isotropic irradiation varies from 6.2 ± 0.5 mrem/yr at the surface of the body to 56 per cent of this value at 10 cm deep, assuming the body is represented by a semi-infinite slab of tissue 20 cm thick. The average D.E. rate at the surface of the body for persons flying at supersonic transport altitudes (∼65,000 ft) ranges from 0.20 mrem/hr to 0.40 mrem/hr depending upon whether the sun is at sunspot maximum or minimum. Experimental measurements, using the spherical moderator technique, confirm the calculated value for the natural dose-equivalent rate.