Direct annihilation fraction of positrons in a neutral low- density galactic environment.
01 January 1986
The fraction of positrons which survive below the positronium (Ps) formation energy in a low density galactic environment can directly annihilate with bound electrons in the gas. The details of the measurement of the survival (direct annihilation) fraction using a low energy laboratory positron beam are presented for H(2) and He. The fraction is found to be higher in H (2) than had been predicted by Bussard, Ramaty and Drachman. The galactic positron line has been shown to be consistent with the lineshape expected for annihilation in a neutral medium based on this measurement and on a theoretical prediction of the direct annihilation linewidth.