Diffusion of helium in a silver-lithium-alloy after neutron irradiation

A helium concentration of 1.1 x 10-5 At% was produced in Li-doped silver by the nuclear reaction Li-6(n,T)He-4. In post-activation diffusion tests, the noble gas production was measured continuously with a mass spectrometer in a static vacumm system in the temperature region between 4100C and 8090C. The isothermal kinetics can be satisfactorily described by the assumption of simultaneous processes of diffusion and capture in traps with vanishing emission probability as stated by Gaus. In accordance with this assumption, the rate of degasification (F) shows an initial rise of tsup(1/2). Diffusion coefficients were determined from this initial region. Owing to the permanent capture, the maximum rate of degasification (Fsub(max)) remains smaller as 1 and increases with increasing temperature, reduced thickness of the probe, and decreasing neutron dose. After maximum degasification below 7000C, further degasification could be observed above 7000C. (orig./AK)