Abstract
It is necessary to know the incident direction of gamma rays to search for the position of radioactive materials or contamination remotely. In order to meet this demand, a new gamma ray detector, which positively raises directional sensitivity against incoming gamma rays, has been developed. This detector is composed of three kinds of different scintillators and a photomultiplier tube. The types of scintillators are NaI (Tl), CsI (Tl), and BGO. The section shape of each scintillator is sectorial of 120 degrees. The one cylindrical scintillator is made by optically connecting three sectorial scintillators. Gamma rays penetrate along a straight path through each scintillator of the detector, and the length of each path is dependent on the incident direction. Therefore the probability of photoelectric effect in each scintillator is changed, according to an incident direction of gamma rays. As a result, the gamma ray counts of three peaks observed in a spectrum obtained by a multi-channel analyzer have dependency with the direction. The response curve of each scintillator with respect to a peak count and an incident direction was made by experiments using a gamma ray source of 137Cs. It has been recognized that these response curves have sensitivity in the total range from 0 to 360 degrees. Therefore the proposed detector has the possibility that the direction can be identified.
