Measurements of Radiation Doses due to Background Gamma Rays by Plastic Scintillators

Abstract

Relative responses of the two cylindrical plastic scintillators (1″ φ × 1″ height, and 2″ φ × 2″) to air doses were calculated for gamma rays of energy ranging from 0.1 to 2.0 MeV with variation of the incident directions. The results of the calculations showed that the relative responses did not practically depend upon the energies and incident directions of gamma rays. On the bases of these results, we measured the dose rates from background gamma rays both out-door and in-door. The dose rates obtained by our measurements inside buildings were 48-68 mr/year. On the other hand, the dose rate from the terrestrial gamma rays was 27.5 mr/ year, which was only one third of the world average. Such lower value was ascribed to the low activity of the soil (composed of volcanic ash) in Kanto district. Also, we estimated the accumulated dose from fission products deposited on the ground (in Chiba City) to be about 30 mr during the period from November 1958 to December 1959.