Temperature dependence of positron trapping in silver and nickel

The Doppler broadened annihilation gamma ray lineshape has been measured for Ag and Ni between room temperature and the melting points by a new technique employing an inert gas positron source. Trapping model analyses yield vacancy formation energies of 1.20 and 1.73 eV respectively, assuming linear temperature dependence of the untrapped positron lineshape. A value of 1.45+or-0.07 eV can be obtained for Ni using an empirical linear relationship between formation energy and the threshold temperature for trapping.