Damage cross-sections of heavy ions in crystal structures

Abstract

The decrease in the intensity of the X-ray diffraction pattern after bombardment by 3 MeV Ar + ions has been measured for several crystal structures. The metamict damage cross-section D M is given by I F / I 0 = exp(− D M · F), I F,0 being X-ray diffraction peak intensities at fluence F, 0. Such cross-sections vary from less than 0.01 nm 2 for materials such as the fluorite structured oxides and for many nitrides which are virtually stable to radiation damage, to cross-sections of about 3.0 nm 2 for α-quartz structured GeO 2 which becomes noncrystalline or metamict readily. Monazite damages rather easily with D M = 0.56 ± 0.13 nm 2. The principal SYNROC compounds, zirconolite, perovskite and Ba-hollandite, have D M values of 0.07 ± 0.03, 0.32 ± 0.11 and 1.0 ± 0.1 nm 2 respectively. Pollucite, spinels and magnetoplumbites have values of D M less than 0.2 nm 2. For a ceramic to remain essenially crystalline ( I F / I 0 = 0.95), after irradiation to a dpa value of about 0.1, the metamict damage cross-section D M should be about 0.02 nm 2. This dpa value corresponds to about 10 19 α-recoil/cm 3 over a period of time of about 10 6 years, as in some proposed radiation waste storage systems. Heavy ion bombardment studies afford a very simple and quick method of simulating radiation effects in solid nuclear waste-forms to complement actinide doping studies.