Helium irradiation effects in single crystals of MgAl2O4

Magnesium aluminate spinel, (MgAl2O4), is a promising material as a uranium free matrix for the transmutation of americium. Fission products and alpha -particles are produced during the transmutation. The impact of alpha-parti cles is simulated by 30 keV He-3 ion implantations at room temperature (RT) with the doses 6.2, 16, 20 and 53 x 10(15) cm(-2). In another set of exper iments a single crystal MgAl2O4 (1 0 0) sample is irradiated with ct-partic les (4.5 MeV) from a Am-241 source at RT to a dose of 1.3 x 10(12) cm(-2). Helium release from the implanted samples was studied by thermal desorption spectrometry (TDS), The numerical analysis of the experimental thermal des orption results of alpha-implanted samples to a very low helium concentrati on (0.0288 appm in the irradiation zone of 12.4 mu m) show that helium rele ase is dominated by helium interstitial diffusion with an activation energy of 1.8 eV. In the case of high dose implantation to 1.74 at.% in the impla ntation zone approximately of 100 nm, helium is released from He-vacancy cl usters with the activation energy of 2.35 eV. The evolution of the helium c oncentration profile in the temperature range from RT to 1483 K is monitore d by neutron depth profiling (NDP), It confirms that the release of helium is governed by dissociation from vacancy clusters, (C) 2000 Elsevier Scienc e B.V, All rights reserved.