Events registration in a fast neutrons spectrometer

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The principle of operation, design, registration system and main characteristics of a fast neutrons spectrometer are described. The spectrometer is intended for direct measurements of ultra low fluxes of fast neutrons. It is sensitive to neutron fluxes of 10-7 neutrons/(cm² s¹) and lower with the neutron energy above 700 keV. The detection efficiency of fast neutrons with simultaneous energy measurement is within 0.02-0.06. The neutron spectrometer was designed taking into account requirements for minimizing the gamma-ray background. It is a calorimeter based on a pure liquid organic scintillator-thermalizer with helium proportional counters as capturers of thermalized neutrons distributed uniformly over the volume. Low-level signal electronics for the spectrometer were designed with signal-to-noise ratio optimization and full pulse shape analysis required for efficient rejection of background events. A data acquisition and processing system is based on fast (100 MHz) two-channel PC/AT interfaced digital oscilloscope. The acquisition software was written in the C programming language.