Breakthrough in pulse-shape based particle identification with silicon detectors

Identification of charged particles is an important method in nuclear spectroscopy. We have achieved a major breakthrough that makes the pulse-shape discrimination (PSD) method with a single solid-state detector comparable to and sometimes better than the traditional telescope technique. By using rear-side injection in over-biased surface barrier n-type Si detectors made from homogeneously doped n-TD silicon, and extracting the pulse-shape information already at the preamplifier level we have reached improved Z and even A discrimination over a wide dynamic range. Previously good separation with the PSD technique required a major degradation of time resolution and inferior energy resolution. Currently we have pushed down the dynamical time range to below 35 ns and reached time resolution of about 200 ps fwhm while maintaining good energy resolution characteristic of silicon detectors. The lowest energy threshold for Z separation of intermediate mass fragments (IMF) achieved with a 250 μm thick detector is equivalent to a range of about 20 μm in silicon. For IMFs with ranges higher than 80 μm of silicon we got full isotope separation. Details of this study are presented, and the application of our method in recent nuclear physics experiments is briefly discussed