  Quantum Monte Carlo calculations of the relaxation energy, pair-correlation
function, and annihilating-pair momentum density are presented for a positron
immersed in a homogeneous electron gas. We find smaller relaxation energies and
contact pair-correlation functions in the important low-density regime than
predicted by earlier studies. Our annihilating-pair momentum densities have
almost zero weight above the Fermi momentum due to the cancellation of
electron-electron and electron-positron correlation effects.
