Design of an alpha spectrometry system for separated measurement of radon/thoron daughters' concentration by lexan PC SSNTD

摘要

A special system has been designed to measure separately the concentration of radon and thoron alpha emitter's daughters in air. The system components consist of collimators, energy degraders, a filter and a lexan PC (polycarbonate) film, which are integrated and connected to a small portable pump. In this spectrometry method, alpha peaks are resulted from registered track size distribution in a wide energy range of 0.9-5.2 MeV under new electrochemical etching (ECE) conditions. Geometric characteristics of the system components are determined based on the optimization between desirable FWHM and detection efficiency by means of the Monte Carlo simulation method using the Fluka code. The results show that ~(218)Po and ~(214)Po from radon chain and ~(216)Po (which is the representative of thoron concentration), ~(212)Bi and ~(212)Po from thoron chain can be measured separately in a mixed field with the FWHM of less than 0.2 MeV. The sensitivity was calculated to be 8.5 and 0.018 (Track cm~(-2) kBq~(-1) m~3 h~(-1)) for radon and thoron, respectively. The radon level can be measured via ~(218)Po concentration using a special measurement setting so that a short-term measurement of equilibrium factor can be performed by this spectrometry method.