Directional characteristics of a monitoring post with triple scintillators

A conventional monitoring post is the equipment useful for check of leakage of radiation or radioactive substance from a nuclear facility. This device regularly offers the data of radiation dose rate (μSv/h, nGy/h) and counting rate (cpm, cps). We have developed a new one which can also measure an incoming direction of gamma ray flux for early discovery of a nuclear accident or adequate interpretation of abnormal data caused from other reasons. This detector is composed of three kinds of scintillators, NaI(Tl), CsI(Tl), and BGO with a photomultiplier tube. The measurement principle is based on the relative change of photoelectric peak counts made by each scintillator depending on the incident direction. This principle in the middle energy range has already been proven by the experiment using 137Cs(662 keV). Then, here the characteristics of the directional sensitivity for low energy (241Am, 60 keV), middle energy (133Ba, 356 keV) and high energy gamma rays (60Co, 1250 keV) have been simulated by using Electron Gamma Shower Program (EGS4), and evaluated by experiments. As a result, this detector has been confirmed to measure the incident direction in a wide energy range. (author)