Sources of radioactivity in heavy mineral concentrate (HMC) from the Holocene beach sand placer at Barrytown, Central Westland were investigated using analytical scanning electron microscopy and radiometric counting. The primary radioactive species are thorium, uranium and daughter radon in monazite and uranothorite. Both minerals exhibit evidence of in‐situ alteration, facilitating release of radon and other radionuclides into the environment. The measured radioactivity of the bulk HMC is 0.22 Bequerels/gram for the solids and 505 Bequerels/per cubic meter for radon off‐gas. Magnetic separation into 0.25, 0.45, 0.75, 1.2, and >1.2 (nonmagnetic) Franz isodynamic separator fractions segregates and (magnetically) concentrates radioactivity. The uranothorite‐rich 1.2 Amp fraction is the most radioactive at 78 Bequerels/gram (solids) and 9665 Bequerels/per cubic meter (radon). Median radon levels measured at residences in and around the Barrytown community exceed those measured elsewhere in New Zealand.
Bradley et al. (Sun,) studied this question.