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In 1988, a 3×1012 s-1 neutron generator named ZF-300 was built at Lanzhou University. The neutron source was used in the programs involving basic nuclear data measurements, irradiation effect researches of materials. Recently, a new intense neutron generator named ZF-400, is being developed for the purposes of fast neutron physics research, such as fast neutron nuclear data measurement by activation method and fission physics. The Cockcroft-Walton accelerator was designed to accelerate the D+ beam of 30 mA to the energy of 400 keV. The designed neutron yields of ZF-400 neutron generator were greater than 5×1010 s-1 for D-D and 5×1012 s-1 for D-T, respectively. In the field of fission physics, a potential-driving model by uniting the empirical asymmetric fission potential and the empirical symmetric fission potential was successfully developed to precisely calculate the pre-neutron-emission mass distributions for neutron-induced actinide nuclei fission. A Monte-Carlo method based on the potential-driving model and Geant4 code was also developed to simulate the fission-fragment yield distribution, kinetic energy distribution and fission neutron spectrum. A twin frisch-grid ionization chamber (TFGIC) detector for the measurement of fission products was also designed and tested. In the field of neutron application technology, in order to meet the development requirements of neutron application technology system, a compact neutron generator with a length of 984 mm and a diameter of 234 mm was successfully developed at Lanzhou University. A bias voltage between the target and the extraction accelerating electrode was produced by a resistance to suppress the secondary electron from the target. D-D neutron yield of the compact neutron generator could be greater than 5×108 s-1 under a pure molybdenum as the drive-in target and the beam energy of 150 keV. The compact neutron generator has the potential to produce D-T neutrons with a yield of more than 1010 s-1. A beam-shaping-assembly (BSA) based on a compact D-T neutron generator was designed for fast neutron radiography, and a fast neutron imaging detector based on micro-channel plates was also developed. Preliminary fast neutron imaging test using D-T neutron generator shows that the spatial resolution of the image is about 500 μm. A detection system to measure 235U enrichment uniformity in nuclear fuel rods based on a compact D-D neutron generator was also designed. Simulation results show that the confidence probability can reach 99% for a relative 235U enrichment deviation of 10% under a D-D neutron yield of 5×108 s-1.

BackgroundBoron Neutron Capture Therapy (BNCT) has been widely recognized around the world as an effective cancer treatment. The accelerator neutron source based on 7Li(p,n) reaction has the advantages of low reaction threshold, high neutron yield, low average neutron energy and easy slowing down. It is the most promising accelerator neutron source for BNCT.PurposeThis study aims to design an accelerator-based neutron source for BNCT, and design a reasonable beam shaping model.MethodsThe Geant4 (GEometry And Tracking) program was used to simulate the neutron source characteristics of protons bombarding lithium targets with different thicknesses at different energies. The accelerator parameter design scheme was proposed by using a 0.2 mm thick lithium target bombarded with 3 MeV protons. Then, the neutron beam shaping assembly (BSA) model was designed and optimized. A combination of "26 cm MgF2 + 10 cm TiF3" was taken as the moderating layer structure with 6Li of 0.08 cm taken as thermal neutron absorption layer and Bi of 1.5 cm taken as γ absorption layer. Finally, simulation of accelerator proton beam at 15 mA was carried out to calculate the optimal material combination and thickness.ResultsSimulation results show that the rate of epithermal neutron flux at the outlet of the moderator reaches 1.16×109 n·cm-2·s-1, the ratio of fast neutron to epithermal neutron Φepi / Φfast is 21.64, the ratio of thermal neutron to epithermal neutron Φepi /Φth is 125.23, and the γ component Dγ /Φepi reaches 1.82×10-13 Gy·cm2·n-1 (epi).ConclusionsThe parameters at the BSA exit designed in this study meet BNCT requirements.

In this research, we used a self-developed compact D-D neutron generator and designed a neutron radiation biological device. The research results showed that lead was the material with the best neutron permeability; thus, hard lead was selected as the structural material for this device. Our research disclosed a phenomenon that differed from conventional wisdom, namely, the dose contribution of the neutrons reflected from the hard lead material at the top of the device was about twice that of the polyethylene material. Therefore, hard lead was also selected for the material of the top reflector in this device. The study also showed that the device had good dose uniformity, and the standard neutron absorption dose in each irradiation zone could be obtained according to the simulation results. This device may further promote the development of future research work such as neutron radiation biological effects and mutation breeding. [ABSTRACT FROM AUTHOR]