Observations of radon at the Kamioka Mine and earthquake prediction

我们新研制了一台水下测氡仪，用于水中氡浓度的测定。安装在容器内的PIN光电二极管是一种阿尔法粒子探测器，当静电充电时会吸引氡族。从^&lt；218&gt；Po(RAA)、^&lt；214&gt；Po(RAC‘)、^&lt；210&gt；Po(RAF)和^&lt；212&gt；Po(THC’)发射的α粒子彼此完全隔离。该系统可用于纯水中氡浓度从0.5(Bq/m^3)到地下水中10,000(Bq/m^3)的大范围半年的观测。对Kamiokande水箱中纯水氡浓度的观测结果表明，该技术对脱气系统的监测是有效的。测量了Kamokande公司不同探测器材料的氡析出率，估算了探测器材料呼出的预计氡浓度约为0.03(Bq/m_3)。这一数值是卡莫坎德地区测得的氡浓度0.5(Bq/m^3)的1/20。该系统可用于断裂带地下水中氡浓度变化较大的三年周期观测。对神冈煤矿1000米深度的地下水氡浓度的观测结果表明，该技术用于地震预报是有效的。赤川断裂带发生3.9级地震前两天半左右，岐阜县中部发生4.7级地震前10天左右，氡浓度显著下降。

We newly developed an underwater radon detector for ^<222>Rn concentration determinations in water. A PIN photodiode, an alpha particle detector, installed inside a container attracts radon families when charged electrostatically. Alpha particles emitted from ^<218>Po(RaA), ^<214>Po(RaC'), ^<210>Po(RaF) and ^<212>Po(ThC') are completely isolated from each other. This system cam be applied to a half year period observation for wide variation of radon concentrations from 0.5(Bq/m^3) in pure water to 10,000(Bq/m^3) in underground water. The observed results of pure water radon concentration in the KAMIOKANDE Tank showed that this technique is valid for the monitor of the degasfication system.Radon emanation rate were measured from various detector materials in KAMIOKANDE.The expected radon concentration from the exhalation in detector materials was estimated to be about 0.03(Bq/m_3). This value is 1/20 of the observed radon concentration 0.5(Bq/m^3) in KAMIOKANDE.This system can be applied to three years period observation for wide variation of radon concentrations in the fault underground water. The observed results of underground water radon concentration at a depth of 1,000(m) in the Kamioka Mine showed that this technique is valid for earthquake prediction. Significant decrease in the radon concentration were observed about two and a half days before a magnitude 3.9 earthquake occurred on Atotsugawa fault, and about ten days before a magnitude 4.7 earthquake occurred on the center of Gifu Prefecture.