新潟県中越沖地震直後の空間放射能  [in Japanese] Variation of atmospheric and ground fissure radon concentration using portable natural gamma ray system while the Niigata Prefecture Chuetsu-Oki Earthquake in 2007  [in Japanese]

The magnitude-6.8 Chuetsu-Oki Earthquake struck at 10:13 a.m. 16^<th> July 2007, off the northwestern coast of Japan in Niigata Prefecture, Japan. The hypocenter was Chuetsu-Oki region 37.33N, 138.36E (17km in depth). The quake started under the ocean about 9km North of Kashiwazaki Kariwa nuclear plant, killing 11 peoples, and flattening several hundreds of buildings. In this study, Radon has measured in air and ground fissures using portable natural gamma ray system on July 16-17, and 20-21^<th>, 2007. The quite high gamma ray of 300-340 cpm was detected on July 21^<th> at Ohminato, Kariwa village which is the nearest of the fault fissure zone. The abnormal increase (200-300cpm) was detected at large deep subsidence and new crack on the paved road. For comparison, normal air radon without earthquake was counted as low as 60-80cpm. The car-borne and hand-borne measurement system was assembled for easily and rapidly detecting full features of the fissures buried in the ground.