RECOVERY OF NEUTRON-INDUCED DEFECTS IN NEAR-STOICHIOMETRIC SPINEL CERAMICS IRRADIATED AT AROUND 500-DEGREES-C

Magnesium aluminate spinel ceramics with different stoichiometry were irradiated with fast neutrons up to 2.3 x 10(24) n/m(2) (E > 0.1 MeV) at around 500 degrees C. Near stoichiometric compositions, average len gth change and corresponding lattice: parameter change by the irradiat ion were very small, but some specimens contracted relatively large am ount. These: specimens were isochronally annealed up to 1000 degrees C . During the annealing, macroscopic length of the specimens whose: len gth reduced by the irradiation showed stepwise increase at around 650 degrees C, acid returned to the pre-irradiation value. On the other ha nd, macroscopic length of the specimens whose length increased very sl ightly due to the irradiation almost: unchanged. The changes in macros copic length matched well with the changes in lattice parameter of all specimens due to the irradiation and post-irradiation annealing. The reason of the stepwise increase in length and lattice parameter during , annealing may be related to the order-disorder transition of cation distribution in spinel.