Continuous Measurement of Environmental Gamma Radiation in Tokyo Using Ge Semiconductor Detector

INTRODUCTION Radon and its progeny are natural radioactive nuclides and exist in various places on the earth. Some of the radon progeny in air and clouds is transferred into rainwater. It has often been observed that gamma radiation at ground level increases on a rainy day. The increase of natural background gamma radiation disturbs the estimates of the influence of artificial radioactive nuclides from the data obtained using monitoring instruments such as a NaI(Tl) scintillation counter. Excessive effort is required to collect rainwater and measure the radioactivity of nuclides for every rainfall event. In order to overcome the disturbance from the natural radioactive nuclides, we developed a gamma ray monitoring system using a Ge semiconductor detector. The energy resolution of the detector is so high that it can identify the nuclides from the energy information. In this paper, we describe the characteristics of the monitoring system and discuss the possibility of the determination of radioactivity in precipitation from the data obtained using the system.