He-ion damage and he-release from spinel MgAl2O4

Spinel is one of the candidate matrices for transmutation of radiotoxic actinides in nuclear reactors. During the transmutation process, large quantities of He are formed by alpha-decay. The behavior of He in spinel and its release upon heating are therefore of large interest. To obtain relevant information, single crystals of stoichiometric spinel MgA(2)O(4) were implanted with lie-ions of three energies: 100, 260 and 2 MeV. The Rutherford backscattering/channeling (RBS/ C) technique was used to measure damage formation as a function of He-fluence, and samples irradiated to different fluences were annealed in a Knudsen cell to measure the release of He. Depending on fluence and heating rate, spalling of the implanted layer, blister formation or release compatible with a diffusion process were observed. The RBS/C measurements showed damage areas at the end of the range of the He, and little damage between the surface and the depth of the range. Spinel is thus structurally stable against He-ions, even at very high concentrations. (C) 2000 Elsevier Science B.V. All rights reserved.