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

用CR-39径迹探测器对氡、钍射气及其子体浓度进行了同步判别测量。用6.0MeV（~ 1 <218>Po，~ 1Bi<212>）、7.7MeV（~ 1 <214>Po）和8.8MeV（~ 1 <212>Po）的α粒子能量对探测器上的蚀坑进行了大小和形状的鉴别。通过在检测器上安装降能器，提高了鉴别能力。使用计算机辅助计数系统自动对刻蚀坑的大小和形状进行分类。氡和钍射子体被静电收集到降能器表面上，以消除从探测器表面附近的空间以降低的能量撞击的α粒子。设计了一个静电收集杯，以防止从附着在杯壁上的子体发射的α粒子，并获得在检测器表面上收集的子体的平坦分布。将该方法应用于富钍射气田氡和钍射气平衡当量浓度的测量。

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.