Pressure dependence of Doppler-broadened positron-annihilation lineshapes in copper, cadmium, aluminium and lead

We have investigated the relationship between bulk positron annihilation characteristics and metal density, independent of thermal effects, in copper, cadmium, aluminum and lead. Measurements were made of the Doppler-broadened annihilation lineshapes of these metals as a function of pressure at room temperature. The lineshapes were deconvoluted into valence (parabolic component) and core Gaussian component) electron contributions. The core fractions and the Fermi energy parameter sigma/sub p/ were obtained from the fitting parameters. The lineshape parameter, F/sub f/, was determined directly from the data. We have found core fraction, CF, and F/sub f/ are proportional to volume, as expected. The extrapolated zero-pressure core fractions, CF(O), agree with other works. The proportionality between the core fraction change and the volume change, #betta#/sub cf/, is approximately one for cadmium and lead, and two for copper and aluminum. The proportionality between F/sub f/ and the volume change, #betta#/sub f//sup p/ is approximately one for cadmium, aluminum and lead, and two for copper. The analogous thermal expansion coefficient, #betta#/sub f//sup T/, generally agrees with #betta#/sub f//sup p/ around the value one. The Fermi energy parameter, sigma/sub p/, is found qualitatively to increase with pressure but at a faster rate than predicted by the free-electron model