Positron Annihilation with Inner-Shell Electrons in Noble Gas Atoms

Measurements are presented of the Doppler broadening of the 511-keV {gamma} -ray line from thermalized positrons annihilating with Ar, Kr, and Xe. The experiments are conducted at low pressures using positrons stored in a Penning-Malmberg trap, which ensures that only two-body interactions are involved. The contributions from annihilation on inner-shell electrons are studied quantitatively in an isolated atomic system for the first time. The spectra are compared with theoretical calculations using a simple Hartree-Fock model to identify the inner-shell contributions. {copyright} {ital 1997} {ital The American Physical Society}