Study of the sensitivity of neutron sensors consisting of a converter plus Si charged-particle detector

With the aim of improving neutron sensors for monitoring external neutron exposure, we have analysed the workings of a converter plus silicon PIN diode detector arrangement. A phenomenological analysis of the conversion and signal generation of different converter materials and their effectiveness is given. The results are compared with experimental measurements. Because of the fundamentally different interactions of thermal neutrons versus high energy neutrons, we study the two species separately. For thermal neutrons, two types of neutron converters were examined, 6LiF (crystalline) and Kodak 10B films. For fast neutrons in the energy range from 1 to 20 MeV hydrogen rich Lucite—PMMA (H8C5O2) and Polyethylene—PE (CH2) converters were studied. ermal neutrons and a pure 10B-converter the theoretical response in counts/neutron reaches a value of BSTOT=0.0684 and for a pure 6LiF-converter LiFSTOT=0.0543. The corresponding experimental responses are 0.0062 for KODAK 10B film and 0.0223 for 6LiF converters. The difference between theory and experiment is understood by the necessity to use a lower level discriminator to eliminate unwanted counts coming from electrons and gammas. In the case of the 10B converter impurities in the converter material reduce the signal. Our analysis for fast neutrons allows us to calculate the ratio of sensitivity for Polyethylene to Lucite, for which we predict a value of 1.6. For the measured sensitivities for PE and PMMA, using an 241Am–Be neutron source, we obtain the values of 0.00225 and 0.0015 respectively, the ratio being 1.5.