Development of aerial gamma radiation survey system, 4

Field experiments have been performed by JAERI since 1982 to obtain fundamental data required for development of aerial radiation survey system. In order to supplement the fundamental radiation data, theoretical calculations have been carried out. The utilized Monte Carlo transport program was verified by simulative calculations of the field experiments, and characteristics data on environmental gamma rays have been accumulated. In this report, the field experiments in 1981 and 1982 were simulated making use of the Monte Carlo transport calculation code YURI developed in JAERI. Comparisons were made between experimental and calculated results for exposure rate and flux density originated from terrestrial sources, and from a point source at height of 2.5 m above the ground. Good agreements between the data verified the transport program. As fundamental characteristics data on environmental gamma rays, spatial distributions of exposure, fluence, energy spectra, angular spectra and average energy were reported and discussed, for terrestrial sources of 40K, 232Th-series and 238U-series, for a plane source on the ground and for a point source at 2.5 m above the ground. (author)