Characterisation of a neutron spectrometer based on a P-I-N photodiode

A proton-recoil spectrometer for neutrons was realised by coupling a commercial P-I-N photodiode with a polyethylene radiator. The minimum and maximum neutron energies which can be detected depend on the thickness of the depletion layer (i.e. on the diode bias voltage). It is worth mentioning that the detector has proved to work unbiased, exploiting the filed funneling effect. This effect is due to a local distortion of the electric field in the depletion layer, leading to the collection of pairs produced in the substrate. The response functions were measured by irradiating the spectrometer with monoenergetic neutron beams, generated at the Van De Graaff accelerator of the Legnaro National Laboratories. Monte Carlo simulations were also performed with the FLUKA code. The effect of secondary charged particles produced by thermal and fast neutrons interactions in the silicon device was also investigated