Distribution of Natural Radionuclides at the Nevada National Security Site.

According to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) publications, contributions of terrestrial gamma doses are mainly from the presence of 40K, and of 238U and 232Th together with their progeny in various rocks and soils. A survey of soil distributions of radionuclides 40K, 238U, and 232Th was performed at the Nevada National Security Site (NNSS) using in situ gamma-ray spectrometry with a high-purity germanium (HPGe) detector. The average activity concentrations of 40K, 238U, and 232Th in natural soils at the NNSS are 867 Bq kg-1 (range from 150 ± 8 to 1297 ± 56 Bq kg-1), 50 Bq kg-1 (range from 29 ± 3 to 74 ± 8 Bq kg-1), and 56 Bq kg-1 (range from 11 ± 2 to 96 ± 10 Bq kg-1), respectively. The concentration at each location is significantly associated with its geological lithology. The terrestrial gamma dose rates around the NNSS were estimated from 26 to 144 nSv h-1 with mean value of 93 nSv h-1. Our results provide useful information about the natural background radiation and radiological effects of naturally occurring radionuclides at the NNSS.