Radiological characterisation and inter-laboratory comparison of naturally occurring radioactive materials (NORM) in...

Naturally occurring radioactive materials (NORM), primarily derived from the uranium-238 and thorium-232 decay series and potassium-40, are present in raw and processed construction materials and can contribute to indoor gamma radiation exposure. This study evaluates the activity concentrations of Ra-226, Th-232 and K-40 in building materials used in Ireland and assesses their radiological suitability for construction applications. Twenty representative building materials were analysed in two phases. The first phase included aggregates, construction sands, plaster and concretes from pre-1964 residential demolition sites. The second phase focused on twelve materials, including particle-size fractions of concrete and aggregates, and aggregates from low- and high-radioactivity regions, cementitious additives (ground granulated blast-furnace slag (GGBS) and two fly ash samples), and imported ceramic tiles. High-resolution gamma spectrometry measurements were conducted in up to three laboratories (Environmental Protection Agency, EPA; University College Dublin, UCD; and University of Cantabria, UC) for inter-laboratory comparison. The Gamma Index (Iγ) was calculated in accordance with European Commission guidelines. Ra-226 activity concentrations ranged from 5.5 to 169 Bq·kg^-1, Th-232 from below detection limits to 206 Bq·kg^-1, and K-40 from 5.4 to 1155 Bq·kg^-1. Concrete, plaster, sands and low-activity aggregates exhibited low radionuclide levels, with Iγ values ≤ 0.4, well below the screening limit for unrestricted use. Particle-size fractionation had little effect on radionuclide concentrations in concrete, while greater variation was observed in Ra-226 in aggregate fractions. One aggregate source showed elevated activity (Iγ ≈ 2.0 ± 0.03), highlighting the importance of geological screening. Cementitious additives and ceramic tiles showed higher activity levels than concrete but remained below regulatory limits. This study supports more sustainable construction practices by providing data for the safe reuse and recycling of building materials. The findings expand the available NORM dataset for Irish construction materials and support their safe use in the built environment.