A SENSITIVE EFFLUENT METHOD FOR MEASURING RADON GAS EMANATION FROM LOW-EMANATING MATERIALS

The fraction of radon (Rn-222) gas emanated from soils and building ma terials is critical in estimating radiation source strengths for human dosimetry. A sensitive method has been developed to measure emanation fractions (E) from sample radon effluents. The method equilibrates sa mples with their emanated radon in sealed cans for 24-30 days. Samples are then assayed for radium (Ra-226) by high-efficiency gamma scintil lation spectrometry that eliminates thorium (Th-232) interferences. Ra don in the can head space is then measured, and E is calculated as the ratio of emanated radon activity to sample radium activity. Values of E measured by the effluent method were compared with corresponding me asurements by the differential gamma assay method. Precisions evaluate d on 259 Florida soil samples indicated 1000-s detection limits for em anating radium of Ra(.)E = 0.02 pCi g(-1) by the effluent method and R a(.)E = 0.5 pCi g(-1) by the differential gamma method. The effluent m ethod has superior precision by a factor of eight for background soils containing Ra(.)E = 0.25 pCi g(-1). The effluent method averaged abou t 8% lower than the differential gamma method on 21 comparison samples . Twenty were within a +/-20% data accuracy objective.