Green D G
Centre for Theoretical Atomic, Molecular and Optical Physics, School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, Northern Ireland, United Kingdom.
Phys Rev Lett. 2017 Nov 17;119(20):203404. doi: 10.1103/PhysRevLett.119.203404. Epub 2017 Nov 16.
γ spectra for positron annihilation in noble-gas atoms are calculated using many-body theory for positron momenta up to the positronium-formation threshold. These data are used, together with time-evolving positron-momentum distributions determined in the preceding Letter [Phys. Rev. Lett. 119, 203403 (2017)PRLTAO0031-9007], to calculate the time-varying γ spectra produced during positron cooling in noble gases. The γ spectra and their S[over ¯] and W[over ¯] shape parameters are shown to be sensitive probes of the time evolution of the positron momentum distribution and thus provide a means of studying positron cooling that is complementary to positron lifetime spectroscopy.
