Positron lifetime spectroscopy in copper

Abstract

The temperature dependence of positron annihilation in copper was investigated by measuring the positron lifetime between 20 and 1070 degrees C. A high-resolution lifetime spectrometer (FWHM 170 ps) with a stability better than +or-1.5 ps over a period of four weeks was used. Data treatment in terms of the two-state trapping model showed the strong temperature dependence of the bulk lifetime tau 'f above 620 degrees C. the rapid increase in tau 'f can be explained by the assumption of trapping during thermalisation of the positrons. The evaluation of vacancy-formation enthalpies is only weakly influenced by such effects if one uses the I2( lambda 1- lambda 2) or the tau methods. For copper the extracted vacancy-formation enthalpy is Evf=1.28+or-0.04 eV.