Vacancy formation energy in thorium by positron annihilation

Abstract
The positron annihilation peak coincidence rate has been measured in thorium from 20 to 1460 degrees C. A gradual S-shaped rise due to positron trapping at vacancies has been observed above 700 degrees C. The peak rate remained unchanged across the FCC to BCC transition at approximately=1345 degrees C, which indicates that positron trapping at vacancies is saturated at this temperature. A trapping-model analysis of the data yields a vacancy formation energy in alpha (FCC)-thorium of (1.28+or-0.23) eV.