Modelling of self-powered detectors for fast neutrons

Self-powered detector is a compact and reliable choice for neutron or gamma flux monitoring in fission reactor cores. In this work, experiments and calculations are done to investigate the possibilities of using this principle of measurement for fast neutron field in the test blanket modules of ITER, the fusion reactor under construction in south of France. Constraints on the physical and nuclear properties are identified for an emitter material responsive to fast neutrons. A few materials including beryllium, chromium, vanadium, silver etc. are selected for test, based on these constraints. A test device in flat geometry is constructed in-house and tested with a 14 MeV neutron generator. It has been found in the experiments that the purely neutron-induced effect is low compared to other effects. Other main contributors to the current signal are parasitic reactions due to high energy gamma and neutrons in emitter or other parts of the detector. These effects are studied with computational simulations. A multi-step Monte-Carlo particle transport method is employed to calculate the response of SPND to relevant neutron and/or gamma spectra. ... mehrA combination of emitter and collector (e.g. beryllium and stainless steel) in representative dimensions is modelled, and then its sensitivity to neutrons and gammas are calculated separately. The effect of change of dimensions of various parts is calculated and compared to find the most neutron-responsive configuration of a combination. Experimental results of gamma irradiation of commercial Rh and Cr SPNDs agree with the calculated values. Further comparison between results of experiments and computational models is underway.