²²² Rn and ²²⁰ Rn emanations as a function of the absorbed α-doses from select metamict minerals

Abstract

Metamict minerals contain uranium and thorium, which contribute to physical degradation or metamictization of their crystal structures over geologic time. The damage occurs primarily through progressive overlapping recoil nuclei collision cascades from ɑ-decay of 238U, 232Th, 235U, and their daughter products. We measured 222Rn and 220Rn emanations from metamict samples of nine oxides (brannerite, davidite, fergusonites, pyrochlores, samarskites, and uraninite), two phosphates (monazites), and eight silicates (cerite, gadolinites, perrierite, rinkite, thorite, turkestanite, and vesuvianite). The total absorbed a-doses ranged from 1.4 × 1015 to 6.1 × 1018 a-decay mg-1 for cerite and uraninite, respectively. The 222Rn emanation coefficients varied from 5 × 10-5% (uraninite) to 2.5% (turkestanite). The 220Rn emanation coefficients varied from 7 × 10-3% (gadolinite Ytterby) to 6.2% (gadolinite Marysin). The lowest 222Rn emanation coefficients occurred among metamict minerals containing the highest concentrations of 238U (i.e., uraninite, samarskites, and brannerite). Overall, the 222Rn and 220Rn emanation coefficients observed in this study fall significantly below previously reported values.