Abstract

Zircon (ZrSiO4) contains small amounts of U and Th substituted for Zr in the crystal matrix. This can cause structural damage through progressive overlap of recoil nuclei collision cascading from α-decay of 238U, 232Th, 235U, and their daughter products. Radioactivity can ultimately lead to metamictization and associated open-system behavior of parent-daughter radionuclides within the mineral. We measured 222Rn and 220Rn emanations, along with uranium and thorium concentrations, from 10 large zircon crystals of differing ages and from different global locations. The calculated total absorbed α-doses ranged from 1.6 × 1014 α-decay mg–1 (Seiland zircon) to 5.3 × 1015 α-decay mg–1 (Grass Lake zircon). 222Rn emanation coefficients ranged from 10–4 % (Renfrew zircon) to 4 × 10–2 % (Miask zircon), while 220Rn emanation coefficients varied from 3 × 10–4 % (Minas Gerais zircon) to 7 × 10–2 % (Miask zircon). Both 222Rn and 220Rn emanation coefficients observed in this study correlate strongly with the absorbed α-dose from the 232Th decay series. Radon emanations, however, do not correlate with the total absorbed α-dose.

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