Properties of a PIN photodiode as a neutron detector

The properties as a neutron detector of a silicon photodiode of type Hamamatsu S3590-02 in conjunction with a multi-channel analyser Alphatron-3C were investigated in an Am-Be calibration field at the department of nuclear engineering at the University of Madrid. Since the photodiode is sensitive to charged particles, we covered it with two types of converters to enable its response to thermal and fast neutrons. To detect thermal neutrons a 2mm thick LiF converter deposited on aluminium support was used. The detector was placed in the centre of a 25 cm diameter paraffin sphere in front of the neutron source. The response of detector with the LiF converter (understood as the integrated peak count of the alphas produced in the reaction of the Li with thermal neutrons) was compared with the response of a calibration neutron dose rate probe as well as with the more accurate ambient dose equivalent rate based on spectrometric measurements of the calibration field. Good correlation between the detector response and the calibration measurements was found and the calibration coefficient of the silicon detector was determined. For the detection of fast neutrons, a polyethylene converter of 2 mm was employed in order to produce recoil protons. Initially, numerical simulations were performed to predict the efficiency of detection and the shape of the energy spectrum of the recoil protons produced in response to the neutrons emitted by the bare Am-Be source. Subsequently, measurements with the source were carried out in order to determine the sensitivity and applicability of the detector to detect fast neutrons. The counting rate as a function of distance and the angular characteristics of the detector were also determined. We discuss the possibilities of using such a photodiode as a neutron dosimeter.