Systematic error in 238U decay chain radionuclides measurements due to 222Rn emanation from reference materials

In high-resolution γ spectrometry 238U decay chain members can be measured by comparing reference material and unknown sample count rates induced by the γ lines assigned to 214Pb and 214Bi. Both 214Pb and 214Bi are daughter radionuclides of 222Rn. This noble gas nuclide can escape from both natural samples, and reference materials. If this escape is not properly accounted for, it could become a serious source of error when determining a radioactivity of a sample. In this work we investigate systematic error due to 222Rn emanation from reference materials. We report 222Rn emanation ratios measured in the IAEA-RGU-1, IAEA-375, IAEA-385, IAEA-434, and IAEA-448 reference materials obtained from the International Atomic Energy Agency, and in materials widely accepted as geological reference materials in the trapped charge dating community, Nussy and Volkegem. In addition, we measured TLDA B-2012–1 which is a material available as a completely sealed block for γ spectrometry in the Landesamt für Denkmalpflege und Archäologie Weimar, Germany and Par 15 sample from reference profile in Lublin Upland (Poland). These materials are frequently used in γ spectrometry laboratories for routine calculations of 238U decay chain members. We found that IAEA-RGU-1, which contains uranium ore, has a negligible 222Rn emanation ratio of ca. 2.2%. Other materials, such as IAEA-385, IAEA-375, IAEA-434, IAEA-448, Nussy, Volkegem and TLDA B-2012–1, exhibited 4% – 35% 222Rn emanation. This has the potential to induce 2.4% – 35% systematic errors in radionuclide concentrations.