The positron annihilation peak coincidence rate was measured in thorium from 20 to 1460C. A gradual S-shaped rise due to positron trapping at vacancies was observed above 700C. The peak rate remained unchanged across the FCC to BCC transition at approximately 1345C, which indicated that positron trapping at vacancies was saturated at this temperature. A trapping-model analysis of the data yielded a vacancy formation energy in alpha (FCC)-thorium of 1.28eV.

Vacancy Formation Energy in Thorium by Positron Annihilation. S.M.Kim, J.A.Jackman, W.J.L.Buyers, D.T.Peterson: Journal of Physics F, 1984, 14[10], 2323-8