Electron emission yields from condensed targets following 2-MeV H+ impact

We have designed an experiment to measure angular and energy double differential low-energy electron emission yields following 2-MeV H+ impact on frozen targets under UHV conditions. We have used thin self supporting films of Cu and Au held at 33K, as substrates onto which the frozen targets are deposited. Initial yield measurements from the Cu and Au substrates show weak features (Auger lines) characteristic of these elements in agreement with previous studies and are very sensitive to surface cleanliness. Although the yields for the frozen targets are highly dependent on target species and thickness, they are relatively independent of substrate material or surface cleanliness. For example the spectra for water-ice show a weak but distinct peak around 15 eV which is independent of water-ice film thickness, whereas our yields from frozen SF_6 show two peaks around 4 and 10 eV respectively which shift with condensate thickness. We also show yields from frozen CO_2 and C_2H_6 and compare them to their gas-phase equivalent double differential cross sections. The motivation for this study lies in testing electron transport Monte Carlo (MC) codes that predict the detailed even-by-event electron distributions produced by ionizing radiation. [Supported by the NIH/NCI Grant No. 1R01CA93351-01A1.]