Environmental Radiation Exposure Rate in Louisiana

Abstract

The environmental radiation exposure rate has been measured using thermolumineseent dosimetry at 26 monitoring stations in Louisiana over a period of 2 yr. Sets of LiF dosimeters that are essentially tissue equivalent in their energy response characteristics were left at each station for 90 d, replaced, and the exposure they received determined. The chips were exposed to a standard source three times during the 2‐yr period to assure their accuracy. On at least two occasions during the study period, samples of soil were taken at each station. These samples were dried, ground, sieved for uniformity, and analyzed by gamma ray spectroscopy. The specific activity of 40K, 137Cs, and some of the decay products of U and Th were determined. The average exposure rate for all stations was found to be 19.6 ± 2.8 µC kg−1 yr−1 (76 ± 11 mR yr−1). The range in values, from 15.0 to 25.5 µC kg−1 yr−1 is generally explained by the variation of the 40K specific activity in the natural soil bodies where the stations are located. The 40K specific activity ranges from 100 to 900 Bq kg−1 across the state. The other activities are also related to soil type, but none vary as dramatically as 40K. The results obtained agree with other more limited surveys and provide a large, reliable baseline to which future studies can be referred when assessing changes in environmental radiation levels.