Possibility of observing the second Born contribution to electron capture at high impact velocities

Abstract

The second Born contribution to electron capture has not yet been unambiguously detected even though it almost surely dominates over the first Born term at sufficiently high energies. Three methods are suggested whereby it might be possible to detect the second Born contribution to the cross section for forward electron capture from a hydrogen atom or molecule or from a helium atom by a lightly charged (bare) ion incident with an energy in the range 10-80 MeV per nucleon. The first method involves measuring the cross section for 1s to 3d capture to check that this cross section exhibits a 1/v¹¹ velocity dependence. The second method involves measuring the angular distribution for scattering angles ranging from zero to a few minutes; at a small but non-zero angle there should be a sharp peak in the angular distribution. For the target a He atom or H₂ molecule, a third possibility is to detect a peak in the energy spectrum of electrons ejected from the target in a direction perpendicular to the beam direction, in coincidence with capture.