著者
石川 徹夫 安岡 由美 長濱 裕幸 川田 祐介 大森 康孝 床次 眞司 志野木 正樹
出版者
Japan Health Physics Society
雑誌
保健物理 (ISSN:03676110)
巻号頁・発行日
vol.43, no.3, pp.253-267, 2008 (Released:2010-08-05)
参考文献数
70
被引用文献数
2 3

Before the 1995 Hyogoken-Nanbu earthquake, various geochemical precursors were observed in the aftershock area: chloride ion concentration, groundwater discharge rate, groundwater radon concentration and so on. Kobe Pharmaceutical University (KPU) is located about 25km northeast from the epicenter and within the aftershock area. Atmospheric radon concentration had been continuously measured from 1984 at KPU, using a flow-type ionization chamber. The radon concentration data were analyzed using the smoothed residual values which represent the daily minimum of radon concentration with the exclusion of normalized seasonal variation. The radon concentration (smoothed residual values) demonstrated an upward trend about two months before the Hyogoken-Nanbu earthquake. The trend can be well fitted to a log-periodic model related to earthquake fault dynamics. As a result of model fitting, a critical point was calculated to be between 13 and 27 January 1995, which was in good agreement with the occurrence date of earthquake (17 January 1995). The mechanism of radon anomaly before earthquakes is not fully understood. However, it might be possible to detect atmospheric radon anomaly as a precursor before a large earthquake, if (1) the measurement is conducted near the earthquake fault, (2) the monitoring station is located on granite (radon-rich) areas, and (3) the measurement is conducted for more than several years before the earthquake to obtain background data.
著者
石川 徹夫 安岡 由美 楢崎 幸範 床次 眞司 石井 忠 須田 博文 山田 裕司
出版者
公益社団法人 日本アイソトープ協会
雑誌
RADIOISOTOPES (ISSN:00338303)
巻号頁・発行日
vol.53, no.3, pp.133-140, 2004-03-15 (Released:2011-03-01)
参考文献数
21
被引用文献数
1 1

Measurements of radon in water have been conducted by many investigators so far. While liquid scintillation counting is widely used for radon-in-water measurements in Japan, there are other available devices such as IM-fontactoscopes and atmospheric radon monitors with bubbling kits. In the present study, an intercomparison exercise was conducted for four devices using water samples with two different radon concentrations. The devices used are : a liquid scintillation counter, an IM-fontactoscope, a pulse ionization chamber with a bubbling kit and a radon monitor (which employs a silicon semiconductor detector) with a bubbling kit. As a result, there was a good agreement among the measured values for other devices than the IM-fontactoscope (differences were within±3%), The atmospheric radon monitors (with bubbling kits) could be useful for field surveys of radon-in-water, considering their portability. On the other hand, the values measured with the IM-fontactoscope deviated from other measure-ment values (47% for sample A and 22% for sample B) . The deviation might be caused by a calibration method for the IM-fontactoscope. Since the IM-fontactoscopes are used at some institutes in Japan even nowadays, it is necessary to check values measured with them for determination of radon-in-water concentrations.
著者
安岡 由美 川田 祐介 長濱 裕幸 大森 康孝 石川 徹夫 床次 眞司 志野木 正樹
出版者
日本地球化学会
巻号頁・発行日
pp.39-39, 2008 (Released:2008-09-06)

神戸薬科大学において,電離箱を用いて、大気中ラドン濃度の連続測定(1984年1月から1996年2月,1989年欠測)をしていたところ,兵庫県南部地震(1995年1月17日)前に,ラドン濃度の異常な上昇が観測された。地殻歪の変化によって,岩石・土壌中の空隙率・空隙連結度が変化し,その結果ラドン散逸量も変化したと考えられる。また,地下水中ラドン濃度や地下水湧水量の変化は,観測地点の局所的な地殻歪を反映しているのに対し,大気中ラドン濃度変化は,ある程度広範囲の平均的な地殻歪変化を反映している。さらに,大気中ラドン濃度の変動パターンは臨界モデル式で回帰することができる。以上のことから,大気中ラドン濃度変化は,地震前兆の観測項目として有用だといえる。