Pulse discrimination between recoil protons and secondary electrons for a silicon diode based neutron spectrometer

The feasibility of the discrimination between protons and secondary electrons was investigated in order to decrease the lower limit of a recoil-proton spectrometer for neutrons based on a silicon p-i-n diode. The simulation of the ionization generated in the detector by protons and electrons and the simulation of the relevant induced currents show that such discrimination is feasible provided that the "rear side injection" configuration and a low noise setup are adopted. The difference between the collecting times of the two pulses is maximized and used for the rising time based discrimination. The neutron spectrometer consists of a 3 mm(2) area, 300 mum-thick silicon p-i-n diode covered with a polyethylene foil on the n-side. The ENC is 720 rms electrons at 20 ns shaping time. Experimental results on monoenergetic neutrons show the effectiveness of this discrimination in decreasing the lower limit of the recoil proton energy spectrum from 1.1 to 0.6 MeV.