EVALUATION OF EQUILIBRIUM-EQUIVALENT CONCENTRATIONS OF RADON AND THORON WITH A HIGH-SENSITIVE PASSIVE MONITOR

采用带CR-39径迹检测器的无源监测仪对氡、钍及其子体浓度进行了同步判别测量。在α粒子能量为6.0MeV(^<218>Po, ^<212>Bi), 7.7MeV（^<214>Po）和8.8MeV（^<212>Po）的情况下，利用探测器上的蚀刻坑的大小和形状进行了区分。利用安装在探测器上的降级器增强了识别能力。蚀刻坑的大小和形状由计算机辅助计数系统自动分类。将氡和钍子体静电收集到降解器表面，以消除从探测器表面附近空间以降低能量撞击的α粒子。设计了一种静电收集杯，防止α粒子从附着在杯壁上的子粒子发射，并使收集到的子粒子在探测器表面呈平坦分布。该方法应用于富钍田氡、钍平衡当量浓度的测定。

Simultaneous and discriminative measurement of the concentrations of radon, thoron and their daughters was performed using a passive monitor with CR-39 track detector. Etch pits on a detector were discriminated with their sized and shapes for alpha particle energy of 6.0MeV(^<218>Po, ^<212>Bi), 7.7MeV(^<214>Po) and 8.8MeV(^<212>Po). Discriminating capability was enhanced by use of a degrader mounted on the detector. Etch pits were automatically classified for their sized and shapes using a computer-aided counting system. Radon and thoron daughters were electrostatically collected onto the degrader surface in order to eliminate alpha particles impinged from the space near the detector surface with reduced energy. A cup for electrostatic collection was designed to prevent the alpha particles emitted from daughters attached on the cup wall and to obtain a flat distribution of daughters collected on the detector surface. This method was applied to the measurement of equilibrium-equivalent concentrations of radon and thoron in thoron-rich fields.