Retrospective assessment of historic radon concentrations in Norwegian dwellings by measuring glass implanted po-210 – an international field intercomparison

The first Norwegian study of historic radon concentrations in 17 dwellings in the high radon areas inNorway has been conducted as part of an international field intercomparison during 1998. Theinvestigation is part of SINI (an acronym for Sweden, Italy, Norway and Ireland) internationalcollaboration on retrospective radon measurements in several European countries having differentclimates and living conditions. The retrospective radon concentration is estimated via measurementsof Po-210, the long-lived decay product of Rn-222 implanted in glass surfaces of objects like pictures,mirrors, cabinet-glass etc, the method called surface trap. Three different surface trap techniques toassess the implanted Po-210 activity and two different procedures to estimate retro radon from Po-210data were used. The Po-210 and the retrospectively estimated radon results agree reasonably well overa wide range of concentrations. Historic radon concentrations were also estimated from analysis of asmaller number of volume trap samples (pieces of spongy materials), and the results compared tothose from surface traps. The retro radon results correlate with contemporary radon results withcorrelation coefficient of 0.877. To evaluate uncertainty in Po-210 measurements due to varyingposition on the glass a study of spatial homogeneity of three sample glasses was conducted andvariations between 12% and 18% were found.