Study on influence of radioactive contamination derived from nuclear power plant accident on building space, 2; Study on measurement method of direction radiation dose rate intended for field survey

Yamamori, Ryo*; Kobayashi, Hikaru*; Honta, Shohei*; Yoshino, Hiroshi*; Nozaki, Atsuo*; Ichijo, Yusuke*; Yoshida, Hiroko*; Furuta, Takuya   

Understanding radiation field is important to predict radiation dose rate in newly constructing buildings in an area widely contaminated by radioactive nuclei. Radiation dose rate at the site is not sufficient, and directional spectra of the radiations are important to consider the shielding effect of the building. Radiation directional spectra can be measured by scintillator partially shielded by lead collimators but the angle of view highly depends on the combination of the scintillator and the collimators. We adopts a method to measure the directional spectra by adopting 3 inch scintillator with placing a plate of lead collimator in front of the scintillator and subtract the values from the spectra measured without lead collimator. We simulates the optimal size of the lead collimator and found that the 15 cm diameter plate placing at 3 cm from the scintillator is the best for our purpose, 90 degree angle of view.