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

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 238 U, 232 Th, 235 U, and their daughter products. We measured 222 Rn and 220 Rn 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 × 10 15 to 6.1 × 10 18 a-decay mg-1 for cerite and uraninite, respectively. The 222 Rn emanation coefficients varied from 5 × 10 -5 % (uraninite) to 2.5% (turkestanite). The 220 Rn emanation coefficients varied from 7 × 10 -3 % (gadolinite Ytterby) to 6.2% (gadolinite Marysin). The lowest 222 Rn emanation coefficients occurred among metamict minerals containing the highest concentrations of 238 U (i.e., uraninite, samarskites, and brannerite). Overall, the 222 Rn and 220 Rn emanation coefficients observed in this study fall significantly below previously reported values.