Electron capture to the continuum and binary ridge structures in positron-hydrogen collisions

The electronic spectrum arising from positron impact of an atom differs greatly from that due to equivelocity proton impact because of the much smaller momentum of the lighter particle. In particular, the authors demonstrate that the features known as the electron capture to the continuum peak and the binary peak in the doubly differential ionisation cross section for 100 eV positron impact of hydrogen reflect the fact that the positron is readily deflected to large angles and suffers substantial energy loss in the collision. They show that the electron capture to the continuum process forms a ridge both in ejected-electron angle and energy and that the shape and position of the binary peak are determined by the great loss of energy by the impinging positron. These results have been obtained from a large-scale simulation of positron-hydrogen collisions using the classical trajectory Monte Carlo technique.