Measurements Of Radon Progeny Concentration And Its Size Distribution Based On The Imaging Plate Technique

Objective Radon and its progeny are the major contributors to human exposure from natural radiation sources. The health effect due to radon exposure has become a world-widely concerned issue as the increased living standard and health requirement of the public. To estimate the health effect, the assessment of radiation dose due to the inhalation of radon and its progeny is required. In general, for accurate assessment of the exposure, the information on the radon progeny concentration, the unattached fraction and size distribution of unattached radon progeny is necessary and important. However, as the limit of measurement equipment, most of the present methods can not be used to measure multiple samples simultaneously or used in some special environments. As the obvious advantages of BaFX imaging plate (IP), such as its large detection area and excellent environmental stability, the new techniques for measuring the concentration of radon progeny, the unattached fraction and size distribution of unattached radon progeny by using IP were studied in this research in order to providing a new method for measuring multiple samples simultaneously.Methods According to the main purposes, the following four parts of researches were carried out in this study.1) Through a serie of experiments, the concentrations of radon and aerosol in the chamber were controlled, and the collection characteristics of filter and wire screen were studied by using the IP technique.2) By considering the overlap effect and the geometric detection efficiency, the optimal distance between the IP and the sample was theoretically studied through Monte Carlo simulations, and the detection efficiencies of radon progeny on the IP were determined through comparative measurements with a calibrated alpha spectrometer. Based on the alpha tracks counting method, a new method for measuring the concentrations of radon progeny by using the IP technique was proposed and testified through comparative experiments.3) Based on the theorectical analysis of the collection efficiencies for different wire screens and sampling velocities, the wire screen and sampling velocity for measuring unattached fraction of radon progeny were chosen for sampling the unattached fraction of radon progeny. By using the IP technique established in this study, a new method for measuring the unattached fraction of radon progeny was also proposed and testified through comparative experiments.4) Based on the theorectical calculations of the collection efficiencies for different combinations of wire screens and sampling velocities, an optimal combination of GSA was selected, and a new method for measuring the size distribution of unattached radon progeny base on the IP technique was also proposed and testified under different aerosol environmentResults The concentration of aerosols in the chamber could still maintain in a range of20000-30000pt-cm-3in10-50min after the injection, it could be used for our experiments. There was a negative correlation between the self-absorption correction factor and pore size of filter. The self-absorption correction factor of the glassfiber filter used in this study was0.986±0.009. The front to total activity ratio of30-,60-,200-,400-mesh wirescreen were0.68±0.10、0.80±0.01、0.90±0.05、0.96±0.03, respectively. The simulation results showed that the optimal distance between the IP and the sample was0.5mm, and the calibrated results indicated that the detection efficiencies of the IP were estimated to be0.226±0.035cts/(Bq-s) and0.345±0.020cts/(Bq-s) for RaA and RaC, respectively. The comparison experiments showed that the concentration of radon progeny measured with the new method was reliable and accurate, and the lower detection limit of EECRn was estimated to be about3.5Bq·m-3. The wire screen and sampling velocity for sampling the unattached radon progeny was chosen to be400-mesh and3.2L·min-1, respectively. The comparison results indicated that the new method by using the IP technique was well agreed with the results measured with another instrument. The new combination of wire screens and sampling velocity in our GSA used to collect the unattached radon progeny consisted of30-,60-,200-,400-mesh wire screen and3L·min-1, and the method for measuring size distribution of unattached radon progeny by the IP technique could be used in different aerosol environments.Conclusions Based on the appropriate sampling device and methods developed in this study, the BaFX imaging plate can be used to measure the concentration of radon progeny, the unattached fraction and the size distribution of unattached radon progeny, and the measurement results are reliable and accurate. Compared with other traditional methods and equipments, the new methods by using the IP have the advantages of high detection efficiency and lower limit as well as high environmental applicability, especially, the new methods can simultaneously measure multiple samples. For further promotion and application the methods established in this study, the detection characteristics for other types of imaging plate are still needed.