A new portable Ge-detector and some data

When the gamma-ray count rate distribution in the office room of the prefabricated house was measured using a portable germanium (Ge) detector, the closer to the window, the greater the gamma-ray effect of radioactive cesium from the surrounding soil was. When the background count rate was measured by applying a simple shield to the detector and the lower limit of detection was examined, the net count rate of Cs-137 became about 1/20 of that without the shield, and the net count rate of Bi-214 and K-40 as natural nuclides became about 1/10 or less and about 1/5, respectively. Under this condition, when a soil sample of about 60 g was measured for 70,000 seconds, the lower limit of detection concentration was about 8 Bq/kg. In situ measurements were performed at l meter height on two open flat lands in Miyagi Prefecture, and the gamma ray dose rate was roughly in agreement with the value obtained by the survey meter. At the northern sites of the prefecture, the contributions of Cs-137 and -134 were larger than those in Sendai City. (A.O.)