Computer simulation of collision cascades in monazite

Collision cascades in the monoclinic mineral monazite have been studied with a modified version of the computer-simulation program marlowe. Most of the calculations were made for the irradiation of polycrystalline CePO/sub 4/ by normally incident 50-eV to 100-keV Ar atoms. A few calculations were made for 1-keV Cu atoms recoiling from lattice sites in a hypothetical form of Cu with the monazite structure. Although there are many fewer replacements and substantially more channeling in the mineral, collision cascades in monazite are generally similar to those in metals in size and shape. The dimensions of the calculated cascades suggest that the amorphization of monazite by Ar-ion irradiation probably commences when collision cascades begin to overlap. The calculations give a detailed view of the structure of the cascades in monazite that should be useful in interpreting radiation effects in proposed nuclear-waste isolation media.