Secondary electron emission from a C-foil resulting from the passage of orientation selected He 2+ molecular ions

Abstract

We have measured the effect of the orientation of the molecular axis on average numbers and number distributions of multiply emitted secondary electrons (MUSE) from a very thin (∼ 50 Å) carbon foil both in the forward and backward directions resulting from the passage of 1 MeV/u He 2 + molecular ions. MUSE was observed in coincidence with a pair of outgoing He 2+ ions detected 3.5 m downstream from the carbon foil. Average numbers of MUSE in the forward and backward directions per incident projectile are 11.5 and 7.5, respectively, when the orientation of the molecular axis is disregarded. Number distributions of MUSE are much wider than the Poisson distribution in any case. They are compared with those which are calculated from the data for 1 MeV/u He + ions. A negative correlation of the number distributions of MUSE in the forward and backward directions was observed. The average number of MUSE in the forward directions is larger when the molecular axis is parallel to the beam direction than when it is perpendicular, but no orientation dependence was observed in the backward direction.