Investigation of environmental dose in the site of nifs, Toki city

The environmental radiation monitoring at site of the National Institute for Fusion Science (NIFS), Toki city. were conducted to examine time variation of environmental dose and its component for CaSO4 (Tm)-UD 200 S thermoluminescence dosimeters measurement. In addition, the simulation using pre-irradiated TLD under real environmental condition was also conducted to estimate its ability in isolation of manmade dose contribution due to nuclear installation.

Using data obtained from the monitoring post which was designed to measure environmental dose components and several time of in situ measurements with various dosimetric methods. it is found that the response of UD 200 S TLD to environmental gamma ray is in good agreement with other dosimetric methods, but in case of cosmic ray there is discrepancy with ratio 0.80±0.13 in comparison with the ionization chamber response. If the published cosmic rays data is adopted for the comparison, then the ratio is 0.87. Based on almost 1.5 years monitoring data there is trend that the pattern of time variation in environmental dose for NIFS site is higher during winter periods than the middle of the year due to time variation of cosmic and terrestrial gamma rays. At given monitoring locations where environmental dose level is reasonably low (at points AA and BB). it was proved by the two-way ANOVA that the TLD system is able to measure an increment as low as 26.2 μ Gy/y or 3 mR/y.