Optimization of the n/γ separation algorithm for a digital neutron spectrometer

An algorithm for the selection of the recoil protons resulting from the neutron interaction with the scintillator is proposed. It is based on the dynamic change of the separation parameter threshold depending on the pulse area. The distributions of the separation parameter for electrons and recoil protons strongly overlap for small pulse areas. In this case, the threshold for the separation parameter is chosen on the basis of the fixed probability of the event false identification. In our work, for example, the contribution of false events was fixed at 1%. With the increase of the pulse area, the distributions for electrons and protons begin to separate well. In this case it is convenient to set the threshold on the separation parameter at the point of their intersection. The use of this algorithm makes it possible to control the fraction of the falsely identified events for the entire range of the pulse areas. This is especially important for low-energy recoil protons, for which the probability of false event identification reaches its maximum. This algorithm was applied to the measurements performed by the time-of-flight method with a 252Cf source. The suppression degree of the prompt gamma-ray peak was 1100 at the neutron detection threshold of 275 keV. The contribution of the falsely identified events for the different parts of the time-of-flight spectrum using the proposed event selection algorithm was studied. The largest contribution to the false pulses was found for the neutron distribution edges - for the neutrons with the energies above 8 MeV and below 0.5 MeV, and it did not exceed 0.23% in the entire range of the pulse areas.