HEAVY ION BOMBARDMENT OF ZIRCON, MONAZITE AND OTHER CRYSTAL STRUCTURES
Heavy ion bombardment with Ar('+) and Kr('+) (3 MeV) ions has been carried out of zircon crystal structures, ZrSiO(,4), ThSiO(,4), DyVO(,4), YPO(,4) and CaCrO(,4), as well as monazite, huttonite, a range of nitrides and several crystals having the fluorite structure. Although X-ray diffraction peak positions and line widths do not vary significantly with fluence for the crystal structures studied, the corrected peak intensities decrease exponentially with fluence. This permits the definition of a Metamict Damage Cross-section D(,M), by (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) where I(,F), I(,O) are X-ray diffraction intensities at fluence F and O respectively. Monazite has a high D(,M) value and is readily converted into a non-crystalline condition and ZrSiO(,4) is found to have a lower D(,M) value. However, whilst metamict zircon is a very common mineral, the mineral monazite is usually found in a crystalline condition. Annealing studies by Differential Scanning Calorimetry show that the crystallization of damaged monazite is completed by about 720K with an annealing rate constant, (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) Thus, monazite would recrystallize in a few hours at the relatively low temperature of 600K. In the case of zircon, recrystallization occurs at much higher temperatures of 1200K. Hence, the metamict condition of naturally occurring minerals can be explained as due to an equillibrium between the damaging process due to radioactive impurities and the annealing process at ambient temperature. Whilst zircon and monazite structures become metamict, CaF(,2), ThO(,2), AIN, GaN, alpha-Si(,3)N(,4) and beta-Si(,3)N(,4) are stable and remain crystalline when irradiated by heavy ions. This leads to a consideration of possible host materials for radioactive waste encapsulation. The constituents of Synroc, Perovskite, Zirconolite and Ba-Hollandite and Pollucite, proposed for ceramic radwaste storage have been examined to determine their relative stabilities to heavy ion bombardment. Studies of heavy ion bombardment of crystal structures can facilitate the evaluation of host materials for radioactive waste encapsulation. Whilst actinide doping experiments take several years to accomplish, heavy ion bombardment studies take of the order of minutes.
KARIGOWDA APPAJI GOWDA,
"HEAVY ION BOMBARDMENT OF ZIRCON, MONAZITE AND OTHER CRYSTAL STRUCTURES"
(January 1, 1982).
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