The Spectrum - dose conversion operator, G(E) function, for air dose rate measurement in contaminated environment

Tsuda, Shuichi  ; Saito, Kimiaki  

Air dose rate monitoring in the environment has been performed since the Fukushima Dai-ichi Nuclear Power Plant accident happened. In the measurement, NaI(Tl) and CsI(Tl) scintillation surveymeters/detectors are used, which are usually used in nuclear power plants and calibrated in a uniform irradiation condition in a radiation calibration field. In general, however, the detector responses are dependent on incident direction and in reality, the incident direction of the photons is not uniform in the environment. In this study, to evaluate the dependence of dose on the photon incident direction, the spectrum - dose conversion operator (G(E) function) for air kerma in a semi-infinite radiation field were obtained using the PHITS code for commonly used NaI(Tl) and CsI(Tl) scintillation detectors. The results indicate that the dose based on the G(E) in AP geometry, which is a common calibration geometry, is approximately 40% higher than that for the environmental monitoring. In the presentation, the results based on measured data will be reported.