The Absorbed Dose in Air of Photons Generated from Secondary Cosmic Rays at Sea Level at Nagoya, Japan

Abstract

Investigations have been carried out to determine the absorbed dose in air of photons generated from secondary cosmic radiation at sea level at Nagoya, Japan. To isolate the contribution from cosmic photons, the pulse-height distributions due to µ particles and electrons were eliminated from the observed pulse-height distribution of a measurement with a 3" diam. spherical NaI(Tl) detector. The pulse height due to µ particles and electrons was inferred from the coincidence technique using two types of scintillation detectors with different sensitivities to photons. To obtain the photon fluence rate for further dose calculation, the pulse-height distribution of cosmic photons was unfolded by the iterative method. The mean and its standard deviation of the absorbed dose in air and fluence rate due to cosmic photons calculated from a one year observation are 2.86±0.05 nGy.h-1 and 0.1342±0.0015 photons.cm-2.s-1, respectively. The absorbed dose in air from cosmic photons was 0.5% lower during autumn to winter and 0.6% higher during spring to summer than the mean taken over the year.