Design and performance of the Water-moderator nested spheres neutron spectrometer

Abstract In this work, a novel neutron spectrometer was designed and its performance was evaluated. The spectrometer is several nested spheres that are filled with water and in the center is a 3He proportional counter The detector part of the spectrometer consists of five concentric stainless-steel spherical shells of different sizes that are nested with each other to form four interlayers with different thicknesses. By filling the interlayers with water or air, 13 thicknesses of water moderator can be obtained. A spherical 3He proportional counter is placed in the core of the stainless-steel spherical shell to detect thermal neutrons. During measurement, different neutron moderation effects are achieved by changing the water-filled thickness of the interlayer. This work uses the Geant4 Monte Carlo code to calculate the response matrix for 100 log-equidistant energies from 10 − 3 eV to 100 MeV. In addition, a highly-integrated electronic circuit, with a STM32L4 series ARM processor as the core, is designed for signal processing and system control. Finally, the energy spectra of 241Am-Be and 252Cf neutron sources was measured using the prototype of the spectrometer. The experimental results are in good agreement with the standard neutron energy spectra given by the IAEA.