ALPHA-DECAY-INDUCED AMORPHIZATION IN COMPLEX SILICATE STRUCTURES

Alpha decay in Cm-doped Ca2Nd8(SiO4)6O2, Pu-doped ZrSiO4, and natural ZrSiO4 minerals results in the simultaneous accumulation of point defects and amorphous regions that both contribute to the macroscopic swelling. A composite model for the macroscopic swelling is used to determine the amorphous fraction as a function of cumulative alpha-decay events. The dependence of the derived amorphous fraction in Ca2Nd8(SiO4)6O2 on cumulative alpha-decay events is consistent with amorphization occurring directly within an individual displacement cascade. In ZrSiO4, on the other hand, the rate of amorphization is lower and the derived amorphous fraction as a function of cumulative alpha-decay events is consistent with models for amorphization occurring as a result of the local accumulation of high-defect concentrations from the multiple overlapping of displacement cascades.