Performance study of the neutron-TPC

Fast neutron spectrometers will play an important role in the future of the nuclear industry and nuclear physics experiments, in tasks such as fast neutron reactor monitoring, thermo-nuclear fusion plasma diagnostics,nuclear reaction cross-section measurement, and special nuclear material detection. Recently, a new fast neutron spectrometer based on a GEM（Gas Electron Multiplier amplification）-TPC（Time Projection Chamber）, named the neutron-TPC, has been under development at Tsinghua University. It is designed to have a high energy resolution,high detection efficiency, easy access to the medium material, an outstanding n/γ suppression ratio, and a wide range of applications. This paper presents the design, test, and experimental study of the neutron-TPC. Based on the experimental results, the energy resolution（FWHM） of the neutron-TPC can reach 15.7%, 10.3% and 7.0% with detection efficiency higher than 10^-5 for 1.2 Me V, 1.81 Me V and 2.5 Me V neutrons respectively.

Design of a neutron-TPC prototype and its performance evaluation based on an alpha-particle test

A neutron-TPC （nTPC） is being developed for use as a fast neutron spectrometer in the fields of nuclear physics, nuclear reactor operation monitoring, and thermo-nuclear fusion plasma diagnostics. An nTPC prototype based on a GEM-TPC （Time Projection Chamber with Gas Electron Multiplier amplification） has been assembled and tested using argon-hydrocarbon mixture as the working gas. By measuring the energy deposition of the recoil proton in the sensitive volume and the angle of the proton track, the incident neutron energy can be deduced. A Monte Carlo simulation was carried out to analyze the parameters affecting the energy resolution of the nTPC, and gave an optimized resolution under ideal conditions. An alpha particle experiment was performed to verify its feasibility, and to characterize its performance, including energy resolution and spatial resolution. Based on the experimental measurement and analysis, the energy resolution （FW-HM） of the nTPC prototype is predicted to be better than 3.2% for 5 MeV incident neutrons, meeting the performance requirement （FWHM〈5%） for the nTPC prototype.

Track reconstruction based on Hough-transform for nTPC

A GEM-TPC prototype, which will be used as a fast neutron spectrometer based on the recoil proton method, is designed and being constructed in Tsinghua University. In order to derive the recoil angle of the recoil proton, tracks of recoil proton in the TPC sensitive volume must be reconstructed. An algorithm based on Houghtransform for track finding and least square method for track fitting was developed in this paper. Based on the Monte Carlo simulation data given by Geant 4, a detailed track reconstruction process was introduced and the spectrum of induced fast neutron was derived here. The results show that the algorithm was effective and high-performance.With the recoil angle of the proton less than 30°, a 4.4% FWHM neutron energy resolution was derived for 5 Me V induced fast neutron, and the detection efficiency was about 2×10^-4.