The Research Of Thermal Neutron Position-sensitive Detector Based On GEM

Neutrons can be used to study the material's microstructure with the features of strong penetrating, distinguishable between close elements, and non-destructive. The reaction cross section of neutron with matter is inversely proportional to its momentum. Therefore, thermal neutrons with lower energy become an important tool for scientific research and new materials' development. As a series of new generation neutron sources around the world have been built to provide high-flux thermal neutron beams, large-area position-sensitive thermal neutron detectors have become an important research subject.In this paper, a solution of position-sensitive thermal neutron detector is given. The basic principle of designing model is based on the nuclear reaction of thermal neutrons with boron-10: 10B (n,α) 7Li. By using of 10B as the converter material, it is to detect emittedαparticles and the product particles 7Li. The neutrons'position information is given by using of the charge center of gravity readout method and the electronic readout system is based on Pads array.We use Monte Carlo simulation software Geant4 to simulate the process of the neutrons'reaction with 10 B and the result ofα-particle distribution within the target. The best thickness of single boron target and the detection efficiency of thermal neutron detector are given; The transportation process of the emitted ions is simulated and the intrinsic position resolution of thermal neutron detection is given; The range and energy deposition distribution of the emitted ions in the working gas are simulated to give the best spatial structure of the detector.According to the simulation results and taking into account of minimizing the spatial structure of the detector and the supply of working gas and the connections of the readout electronics, the overall framework of the detectors and components are designed by the mechanical design tools of AutoCAD.On the request of working gas for the gas detector, Ar+CO₂ are selected as the working gas of the detector. According to the Garfield simulating the multiplied results of several combinations of the mixed gas, the proportion of the gas mixture is given. And such a working gas supply system is established.According to the requirements of the position resolution and take into account of the complexity of the electronic readout system, the charge collection plate is designed based on the Pads array readout mode by the tool of Protel.The best spatial structure of THGEM is given by the electromagnetic field simulation software of Maxwell and Garfield. The strength of the transmission field and that of drift field which are needed to achieve electron multiplication are also given. And based on the above results, the THGEM for experimental testing and the voltage distribution board which can provide different voltage to the components of the detector are designed by the tool of Protel. The establishment of gas supply system and the high-voltage power supply system is completed.We study the method of preparing the thermal neutron convertor boron film. Powder metallurgy is used to prepare the boron target for the PLD experiments. According to substrate conditions of the thermal neutron converter, the aluminized polyimide film is selected as this substrate. The experimental scheme of preparing boron films by PLD is proposed and the morphology and the composition of these prepared boron films are analyzed. From the results, we can see that the surface of the prepared boron film is smooth, without cracks. It can be used as thermal neutron converter, but the content of boron on the sample surface is relatively low, and the film thickness is not ideal, so the preparation method needs to be improved.Experimentally, only a preliminary part of the experiment is carried out. The high-voltage testing experiment and the leakage current of THGEM measuring experiment are completed; The experiment to measure the energy spectrum of 5.9keVγ-ray is still in progress.