P-PARTICLE, D-PARTICLE AND ALPHA-PARTICLE DISCRIMINATION IN NRA - THIN, ADJUSTABLE SENSITIVE ZONE SEMICONDUCTOR-DETECTORS REVISITED

Overlapping peaks arising from particles of different types in complex NRA energy spectra may be unscrambled by using partially depleted semiconductor detectors with well chosen sensitive zone thicknesses. The latter should range from approximately 30 to approximately 100-mu-m for removing proton or deuteron peaks from a typical alpha particle energy interval between 1.5 and 12 MeV. It is difficult to find commercial detectors with such characteristics as they are usually made from silicon of too high a resistivity. Special, large area detectors prepared in nominal 500 OMEGA-cm silicon were investigated for their response, both in energy equivalent amplitude and spread, to protons, deuterons and alpha particles as a function of their energy and of the applied bias voltage. The results may be interpreted in terms of charge collection efficiency depth profiles extending behind the depletion region. If turns out that the effective sensitive thickness of such detectors may be varied continuously over a wide range so that it may be tuned, in combination with a well chosen Mylar absorber, to the optimal value required for unscrambling a large variety of complex spectra, arising from deuteron or He-3 beam induced reactions. The results suggest that it is possible and desirable to produce detectors with well defined discrimination characteristics. The advantages of this simple method with respect to dE/dx telescope based particle identification techniques are discussed. Various applications to the NRA of light isotopes are presented.