The Development Of Novel High-efficiency Fast Nurtron Detector Based On Triple GEM

Based on reading literatures, proposing concept, writing simulation program, mechanical design and assembly as well as testing, the development and test of the novel high efficiency Triple GEM-based (Triple Gas Electron Multiplier-based) fast neutron detector prototype is completed in present work. The obtained results show that the developed prototype meets the purposes, which confirms the rationality and practicality of the prototype. Detailed information and results of this work are summarized into the following four sections:Firstly, the multi layers high-density polyethylene structure as a novel neutron conversion technique is proposed. And its rationality and performance are fully simulated by the software of ANSYS, Garfield++and Geant4, especially for D T (14MeV) neutron. According to the simulation results, the value of the neutron conversion efficiency reaches the maximum value around0.38%when the single layer of HDPE thickness is2400μm and the gas interval is500μm. In addition, the2400μm thick conversion, coupled with the gas interval of500μm, is considered as a conversion unit. The results show that when the number of conversion unit is up to400layers the neutron detection efficiency can reach about2.3%, which is about one order of magnitude higher than that of the currently available data in the world. Meanwhile the different height of the incident fast neutron on the detector is reconstructed. The results show that the reconstruction accuracy is better than2.6%.Secondly, the Single GEM detector and Triple GEM detector is developed, including mechanical design, processing, assembly, and basic performance testing at55Fe of5.9keV X-ray source. Working gas is the mixture of Argon and Carbon Dioxide (volume ratio of80:20). The read out anode is a single-side PCB using micro-strip structure with a sensitive area of100×100mm2. The number of the total strips are496, each strip width is110μm and an interval of two strips is80μm. Experimental results show that,when the bias voltage of the GEM is451V, the energy resolution and the effective gain of Single GEM detector is about17.6%without any collimator and around of5.0E2, respectively. The bias voltage of Triple GEM detector is provided by a passive resistor divider. When the bias divider voltage is2373V, its energy resolution and the effective gain is respectively about19.2%with2mm hole collimator and around of5.0E4. Its detection efficiency and the time resolution is98%and22.6ns, respectively. Thirdly, the transportation of fast neutron and its different interactions with the material in the GEM detector are simulated. The neutron sources include D T, D D (2.45MeV) and Am Be source.Simulation results show that among the secondary particles generated by the incident neutron, the main contributions to the total energy deposition are from recoil protons induced in hydrogen-rich HDPE or Kapton (GEM material) and activation photons induced by neutron interaction with Ar atoms. Their contributions account for90%of the total energy deposition.Fourthly, the design of multi layers HDPE conversion, processing and combining it with a Triple GEM to form a novel high efficiency fast neutron detector is completed. Experimental results show that, when the number of conversion layer is38, its effective neutron response is more than four times higher than that of single layer conversion technique.