A recoil-proton spectrometer based on a p-i-n diode implementing pulse-shape discrimination

A recoil-proton spectrometer was created by coupling a p-i-n diode with a polyethylene converter. The maximum detectable energy, imposed by the thickness of the totally depleted layer, is similar to6 MeV. The minimum detectable energy is limited by the contribution of secondary electrons generated by photons in the detector assembly. This limit is similar to1.5 MeV at full-depletion voltage and was decreased using pulse-shape discrimination. The diode was set up in the 'reverse-injection' configuration (i.e. with the N+ layer adjacent to the converter). This configuration provides longer collection times for the electron-hole pairs generated by the recoil-protons. The pulse-shape discrimination was based on the zero-crossing time of bipolar signals from a (CR)(2)-(RC)(2) filter. The detector was characterised using monoenergetic neutrons generated in the Van De Graaff CN accelerator at the INFN-Laboratori Nazionali di Legnaro. The energy limit for discrimination proved to be similar to900 keV.