Study On Neutron Polarization And Detection Devices

Neutron have wide applications in fields such as physics,nuclear engineering,and materials science,and is important probes at the microscopic scale.Back-n white neutron source is an excellent neutron research platform.The magnetic field is the main factor affecting motion of neutrons for neutrons can’t be charged.Neutron Spin Filter(NSF)utilizes polarized ~3He gas to selectively filter out neutron spins of a certain direction,thereby obtaining polarized neutrons.Polarized neutron have stronger material detection capability and is specifically used to study the magnetic and detect magnetic field distributions in materials.~3He is both the working gas of a typical neutron detector proportional counter and an important material for polarized neutron production.Studying the reaction of neutrons with polarized ~3He establishes the theoretical basis for polarized neutron experiments.Study on neutron polarization and detection devices provide a foundation for future neutron polarization experiments and exploring T-Violation at Back-n.This paper introduces neutron detection technology and neutron polarization technology,with a focus on ~3He-based neutron detection and polarization devices.Firstly,in order to achieve real-time detection of neutrons during the neutron polarization process,a neutron detection element that can be installed in the polarized~3He NSF was designed,fabricated and studied.Test results showed an exponential relationship between the signal amplitude of the detection element and the external power supply and proof that it has particle detection capability.Secondly,to address the low pressure of polarized ~3He in the metastable optical pumping and the high neutron flux of the Back-n,research was carried out on low-pressure pure helium gas proportional counters,and a flow-type proportional counter with an embedded radioactive source was designed and fabricated.Theαdetection signal and electron drift of the detector were simulated with Geant4 and Garfield++Monte Carlo programs.αsource testing experiments were designed and carried out for the low-pressure pure helium gas proportional counter,determining the stable operating pressure range for the low-pressure pure helium proportional counter to be 0.25-1 atm,and demonstrating its neutron counting capability.Finally,to confirm that the white beamline can be used for polarized neutron calibration and that polarized ~3He has a neutron reaction cross section different from that of normal ~3He,a neutron spin filter for polarized ~3He was designed and fabricated.The internal ~3He polarization rate of the neutron spin filter was measured to be greater than 50%with a relaxation time of more than 220 hours using the EPR electron paramagnetic resonance system.A polarized ~3He white neutron transmission measurement experiment was conducted using an online polarization system,providing primary data for calculating the neutron reaction cross-section of polarized ~3He.The experiment was carried out in a style consistent with scientific literature.