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

用带CR-39径迹探测器的无源监测仪同时和区分地测量了氡、钍及其子体的浓度。探测器上腐蚀坑的大小和形状分别为6.0 MeV(^&lt；218&gt；Po；^&lt；212&gt；Bi)、7.7 MeV(^&lt；214&gt；Po)和8.8 MeV(^&lt；212&gt；Po)。通过使用安装在探测器上的降解器，提高了识别能力。使用计算机辅助计数系统对蚀刻坑的大小和形状进行自动分类。为了消除从探测器表面附近撞击的能量降低的阿尔法粒子，将氡和Thoron子体静电收集到降解器表面上。设计了一种用于静电收集的杯子，以防止附着在杯壁上的子体发射的阿尔法粒子，并获得收集在探测器表面上的平坦分布的子体。将该方法应用于富Thoron场中氡和Thoron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.