Impact of alpha self-absorption on personal air sampling in NORM operations

Personal air sampling (PAS) is used to assess worker intake of airborne radioactivity in operations processing minerals containing naturally occurring radionuclides. Subsequent alpha particle counting of the PAS filter may be affected by self-absorption of the alpha particles in the dust matrix or filter, depending on the dust loading on the filter and the size of particles collected. This review investigates the potential for self-absorption on air sampling filters via a literature review and by applying a formula to correct past PAS data from the mineral sand industry. The findings indicate that PAS estimates of intake were consistently under-stated by at least 40% across work categories engaged in the operation and maintenance of mineral sand separation plants. An alpha particle self-absorption greater than 50% was derived when dust loading on the PAS filter exceeded 3 mg·cm^-2. The findings demonstrate that historical PAS data in industries where self-absorption effects are neglected can substantially underestimate worker radionuclide intakes and doses, with important implications for retrospective dose assessment.