Antiproton slowing down, capture, and decay in low-pressure helium gas

Data on (p) over bar slowing down and capture in helium at 1 and 0.2 mb at room temperature are presented and compared to the corresponding previously publicated data in molecular hydrogen and deuterium. A Monte Carlo simulation containing a low-energy extrapolation of measured (p) over bar electronic stopping power in helium gas, screened Rutherford collisions, and simple cascade mechanisms is able to reproduce the gross features of the data, but cannot explain some nontrivial details of the measured distributions.