Comparison of environmental radiation dosimetry and gamma-ray spectroscopy

During the period 1975-1980, direct radiation dose rates were measured at 16 fixed locations in the vicinity of the Joseph M. Farley Nuclear Plant, Houston County, AL, by exposure of TLDs which were read quarterly. The average quarterly dose rates using LiF chips varied widely over the 6-yr period and were divided into 2 distinct population groups of 4 and 2 yr each, corresponding to the vendor labs supplying and reading the TLDs. The simultaneous exposure of CaSO4:Dy TLDs for 2 yr gave a third set of values which fell between the 2 LiF groups. During the period December 1976-November 1980, simultaneous pressurized ion chamber (PIC) and in situ Ge(Li) gamma-ray spectroscopy measurements were made at the same locations at approx. 6-month intervals. The PIC exposure rate values were relatively constant for each location except for 1 measurement at the end of a long dry period broken by showers of rain. The average PIC dose rate values were in good agreement with the average 2-yr LiF TLD values. Also, good agreement resulted from converting the in situ radioactivity values to dose rates using conversion values previously published. Using the in situ Ge(Li) gross gamma count rates, and a new equation developed by the authors for calculating exposure rate, resulted in excellent agreement with both individual and average PIC values. The natural radioactivity and fallout 137Cs in the soil showed little variation for a specific site, but varied widely between some sites. With the event of rain at the end of a long dry period, there was a large increase in 214Bi and 214Pb activity detected. Short half-life manmade radionuclides were seen for a few months following several atmospheric nuclear tests by the People's Republic of China.