Tokonami S, Takahashi F, Iimoto T, Kurosawa R
Division of Human Radiation Environment, National Institute of Radiological Sciences, Chiba, Japan.
Health Phys. 1997 Sep;73(3):494-7. doi: 10.1097/00004032-199709000-00008.
In order to easily measure the activity size distribution of radon progeny, a new instrument was developed that can determine their activity median diameter in a low level environment within 90 min. A four stage low-pressure cascade impactor was used. The particle size cut-off points were >2,100, 700, 210 and 70 nm, based on a particle density of 1 g cm(-3). A 300 metal wire screen diffusion collector facing with a silicon semiconductor detector was placed within the first air inlet in order to measure unattached radon progeny concentrations and also to prevent unattached progeny from entering the impactor. Silicon photodiodes, from which the ceramic windows were removed, were installed in each stage of the impactor. Alpha particles could be effectively detected with 46.2% efficiency as radon progeny were directly collected on the detecting surface of the photodiode. The surface of the photodiodes was coated with silicon grease to prevent particle bounce-off. An inline-type filter holder with a silicon semiconductor detector was connected at the exit of the impactor in order to collect the remaining radon progeny and to measure their concentrations. The instrument was used to concurrently measure the size distribution of radon progeny and the aerosol in the natural environment. The results indicated that the activity median diameter fell in between the median diameter of the aerosol derived from number statistics and that derived from surface-area statistics. A negative correlation was found between the unattached fraction (f(p)) and the activity median diameter.
为了便于测量氡子体的活度粒径分布，开发了一种新仪器，该仪器能够在低水平环境中于90分钟内测定其活度中值直径。使用了一台四级低压串级冲击器。基于颗粒密度为1 g cm(-3)，颗粒尺寸截止点分别为>2100、700、210和70 nm。在第一个进气口内放置了一个面对硅半导体探测器的300目金属丝网扩散收集器，以测量未附着的氡子体浓度，并防止未附着的子体进入冲击器。在冲击器的每个级中都安装了去除了陶瓷窗口的硅光电二极管。由于氡子体直接收集在光电二极管的检测表面上，因此能够以46.2%的效率有效检测α粒子。光电二极管表面涂有硅脂以防止颗粒反弹。在冲击器出口处连接了一个带有硅半导体探测器的在线式过滤器支架，以收集剩余的氡子体并测量其浓度。该仪器用于同时测量自然环境中氡子体和气溶胶的粒径分布。结果表明，活度中值直径介于数量统计得出的气溶胶中值直径和表面积统计得出的气溶胶中值直径之间。发现未附着分数（f(p)）与活度中值直径之间存在负相关。
