A Monte-Carlo Calculation of the Neutron Sensitivity of Self-Powered Detectors

Self-powered (s-p) detectors are useful for incore neutron measurements in nuclear reactors because of their small size, ruggedness and simplicity. In one type of detector, a delayed current results from the beta activity induced in the device by the neutron flux while a second type gives an instantaneous response due to the compton electrons produced by the gammas released following the capture of neutrons in the device. To test these physical models and more importantly, to point the way to improvements in design without having to resort to excessive experimentation, a Monte-Carlo model was constructed to allow computations to be made of the response of both types of detector. The calculations were performed for Rh and V delayed and Co instantaneous detectors with emitter diameters of .051 cm and insulator thickness of .025 cm in all cases. The agreement with experiment was fairly good and the small discrepancies which occur are discussed in the paper.