Issue of air dose rate measurement using survey-meters

Tsuda, Shuichi  ; Saito, Kimiaki  

Dose rate monitoring in air in the environment has been performed since the Fukushima Dai-ichi Nuclear Power Plant accident happened. The reliability of detectors such as survey-meters is ensured under a controlled set of standard conditions in a radiation calibration field. However, the calibration is performed only in a uniform irradiation condition in general, but in reality, the incident direction of the photons is random in the environment. Since detector responses are dependent on incident direction, except for spherical detectors, it is necessary to evaluate the reliability of the measured dose. In this study, using the PHITS code, dose rates in air of a common NaI(Tl) scintillation survey-meter and CsI(Tl) detectors used in the KURAMA system are calculated in a semi-infinite radiation field. In the presentation, the dependence of the dose rates on the incident direction of photons will be shown.