Research On The Performance Of Filters For α-Radioactive Aerosol Sampling

With the rapid development of society, people pay more attentions to the healthproblems caused by radiation in the environment, most of the radiation comes fromnatural radioactive aerosols, as the major component of natural radioactive aerosols,radon daughters should be monitored as rapidly and accurately as possible. Nowadays,it is most used that using filters to collect radon daughters, so choosing right filters isvery important.In our country, most studies on the performance of filters for radioactive aerosolcollecting has been reported in the1980s and1990s,at that time,the main filters wereplastic fiber filters and glass fiber filter,so most studies were about glass fiber filterand mixed cellulose ester membrane which were made in the laboratory,but littleabout nuclear pore membrane.And the samples were measured by total alphameasuring instrument using total alpha measurement.In this paper,several typical mixed cellulose ester membranes produced at homeor abroad were studied,especially for the heavy ion membrane(nuclear poremembrane),which filling the gap between our country and abroad on the use ofcollecting radioactive aerosol.The experimental part of this paper was finished in theradon laboratory of South China University. The Concentration of Radon daughterswas monitored by ELPI, and the sampling system was improved and calibrated.Filters with radon daughters were measured by the ORTEC eight channels alphaspectroscopy workstation,which can measure several samples in the same time andstudy the overlap factor and surface collection performance of the alpha spectrum,thiscannot achieve in the past.In this paper,the measurement of filters performance wasimproved.Considering that the thickness of the filters should not be larger than a half of the range while alpha particles pass through the filters, when measuring theself-absorption factor in use of positive-negative-cover method. In this paper, mixedcellulose ester membrane produced by Milipore corporation was chosen as thestandard filter, the self-absorption factor was measured both ofpositive-negative-cover method and series method. The overlap factor while staticdeposition and dynamic sampling were studied.Comparison on the performance of different filters for radioactive aerosolsampling shown, Mixed cellulose ester membrane produced by Milipore corporationwould be the best choice, and have many types. Heavy ion membrane has rather lowself-absorption loss and high surface collection characteristics, is more suitable forsmall flow sampling. Although the low resistance of glass fiber filters, it’s used forlarge flow sampling in most cases due to its large mass thickness and highself-absorption loss. In this paper, monitoring means for performance of filters forradioactive aerosol sampling was further improved, meanwhile, references andsuggestions of selecting filters for radioactive aerosol sampling were provided.In this paper, performances include filter efficiency,self-absorption,surfacecollection performance and resistance were studied,which provide the basis for filterchoosing,testing and correction.The studied also shown that, mixed cellulose estermembrane would be the best choice which have many types,heavy ion membrane hasrather low self-absorption loss and high surface collection characteristics,which ismore suitable for small flow sampling. Although the low resistance,glass fiber filterswould be used for large flow sampling in most cases due to the large mass thicknessand high self-absorption loss.