Trial of application of TLD to environmental monitoring in water region

Thermoluminescent dosimeters (TLD) are utilized for environmental radiation monitoring, especially for the low dose measurement around nuclear plants, in relation to the realization of ALAP criteria recently. The TLDs are available to detect the concentration of MPCw of radioactive nuclides including β-emitters such as 3H and 90Sr in water and also suitable to be used in water environment because of easiness of handling, high sensitivity and water endurance. The experimental results at the fundamental stage and the field measurement and the measurement of environmental water samples in a laboratory are presented. The experimental TLD elements used were CaSO4 (Tm) series and LiF (Mg) series. The calibration was carried out with a 60Co source for γ-ray, and 68Ni, 147Pm, 99Tc, 204Tl and 32P sources for β-ray. The experiment was conducted for 40K, 137Cs and 147Pm solutions in the water vessel of about 2000 ml inserting three TLD elements. On the other hand, the dose was calculated theoretically. The characteristics of the TLD elements CaSO4 (Tm), LiF (Mg) and LiF (Mg, Cu, P) are shown, and the calibrated results of the TLDs NTL-500G and UD-110S utilizing the 60Co source in the air are given. The relation between the measured dose and the calculated dose in the air, the relation between the calibration constants and the maximum β-ray energy used, the relation between the dose absorbed by TLDs and the distance from a point source of 60Co in water, the γ-spectrum and γ-ray emitters in sewerage water from the RI Laboratory of the Kinki University, the measuring points in the vicinity of the Mihama nuclear power plant, and the dose measurement data in the coast area of the Mihama plant utilizing NTL-500G and UD-110S, which indicate less than 1.2 mR/day, are presented as the test results. (Nakai, Y.)