DOSE-EQUIVALENT RATE FROM COSMIC RAY NEUTRONS

On the basis of published cosmic ray studies, the dose-equivalent [D. E.] rate due to naturally occurring neutron radiation is calculated to be 11.8 [plus or minus] 1.0 mrem/yr for a small piece of tissue in air at sea-level and at a location with geographical coordinates (lat. 55[degree]2[image]N, long. 3[degree]21[image]W). It is deduced that the neutron dose-equivalent experienced by the population at sea-level for isotropic irradiation varies from 6.2 [plus or minus] 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 ([image]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.