Pressure Dependence of Positron Annihilation Rates in the Alkali Metals

The annihilation rate of positrons in the alkali metals has been measured at room temperature for pressures up to 55 kbar. The observed departure from simple predictions of the free-electron gas model are explainable on the basis of changes in the fraction of core annihilations. This interpretation is not, however, consistent with the changes in the Doppler-broadened line shape.