Pulse-height defects for heavy ions in a silicon surface-barrier detector

Abstract

The pulse-height vs energy response of a surface-barrier detector was measured for the ions He, C, O, Al, S, Ni, Cu, Ag, Au and U. The detector was a “heavy-ion” type, with high field strength. The ions were obtained by elastically scattering oxygen and sulfur beams on the appropriate targets. The lighter ions (up to sulfur) showed little or no pulse-height defect (PHD). Heavier ions had a significant PHD which increased with increasing energy, and their response curves were non-linear at low energies. The highest energies at which the PHD was measured were: Ni, 58 MeV; Cu, 18 MeV; Ag, 45 MeV; Au, 31 MeV; and U, 26 MeV. The total PHD is described in terms of three contributing parts: a window defect, a nuclear-stopping defect, and a residual defect, which is attributed to charge recombination. The residual defect is shown to be proportional to the difference between the electronic stopping power of the ion in silicon and a constant, in agreement with a simple model of the recombination defect. The constant is the critical value of the stopping power, below which no recombination occurs. Although there is insufficient data on which to base a practical scheme for calibrating detectors for heavy ions at the present time, some features which appear necessary to such a scheme are pointed out.