Regensburg 2000 – wissenschaftliches Programm

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DS: Dünne Schichten

DS 32: Ionenimplantation V

DS 32.3: Fachvortrag

Donnerstag, 30. März 2000, 16:15–16:30, H31

He-Ion Damage and He-Release from Spinel MgAl₂O₄ — •R. Fromknecht¹, J.-P. Hiernaut², Hj. Matzke², and T. Wiss² — ¹Forschungszentrum Karlsruhe, IFP, 76021 Karlsruhe — ²European Commission, Institute of Transuranium Elements, 76021 Karlsruhe

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 a-decay. The behaviour of He in spinel and its release upon heating are therefore of large interest. To obtain relevant information, single crystals of stoichiometric spinel MgAl₂O₄ were implanted with He-ions of two energies: 260 keV and 2 MeV. The Rutherford backscattering/channeling 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. Upon fast heating and at high fluence (∼5·10¹⁶ ions/cm²), a large release peak was observed at ∼1150 K, followed by diffusion-like release. Profilometry showed that a cylinder defined by beam spot size and range of the He-ions was spalled off, probably due to the formation of overpressurized He-bubbles. At lower fluences and/or slower heating, this spalling was not observed and He-release was more compatible with a diffusion process. The RBS/channeling measurements showed damage peaks at the end of the range of the He, and little damage between the surface and the depth of the range. These results are discussed in the context of the innovative concept of nuclear transmutation of long-lived actinides.