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Environmental Radiation Exposure Rate in Louisiana¹

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.

Key Words: dosimetry • thermoluminescent dosimeters • ⁴⁰K • soils

¹ The research reported here was part of a larger study to determine values of environmental radiation and radioactivity, a study supported by the Research and Development Fund of the Louisiana Board of Regents.

² James N. Beck is Professor of Chemistry at McNeese State Univ. in Lake Charles, LA 70609. Dean F. Keeley and John R. Meriwether are Professors of Chemistry and Physics, respectively, at the Univ. of Southwestern Louisiana, Lafayette, LA 70504. Ronald H. Thompson is Professor of Chemical Engineering at Louisiana Tech Univ. in Ruston, LA 71272.

Received for publication March 26, 1986.