The enhanced yield of nitrogen ions backscattered at 1800

The charge-state dependence of the enhanced surface yield of 3 MeV nitrogen ions scattered within a narrow acceptance angle dTHETA about 1800 has been measured for targets of Au, Ta and Ag. An enhancement of greater than two, together with a slightly larger enhancement for the higher charge states than the lower charge states, was seen for all targets studies. The dependence of the enhancement on dTHETA about exactly 1800 has been measured for Au targets for 0.10 < dTHETA < 1.00. The energy spectra show that the enhancement persists to a depth of about 30 nm and peaks at about 8 nm in each case. The enhancement ratio has its peak value at the surface, which might reflect the fact that a smaller value of dE/dx is operative for the anomalous component of the 1800 scattered particles. This in itself would be responsible for a component of the yield enhancement observed. The data are qualitatively in accord with the concept of path reversibility, although the extent of the enhancement for the silver data is surprising, since the kinematic energy loss in scattering, in this case, is large. (orig.)