Study On The Performance Of NMCP Detectors With Different Neutron Conversion Modes

With the construction and development of high flux neutron sources,neutron imaging has become an important non-destructive testing method,which has the characteristics of complementing the advantages of X-rays.In recent years,energy-selective neutron imaging has gradually become a hot research topic.By selecting neutron energy,it can realize the analysis of the microstructure,defects,morphology,and other information inside materials and devices.It will provide a powerful means for non-destructive testing in the manufacturing process of space shuttle blade,aircraft carrier deck and other major engineering equipment components.Energy selective neutron imaging requires detector has high spatial resolution and fast time response.Neutron sensitive microchannel plate（n MCP）is one of the favorable choices for energy selective neutron imaging detectors due to its high detection efficiency,spatial resolution and excellent time resolution.In this paper,the performance of n MCP detectors with different neutron conversion methods are studied through simulation and experiment.The neutron beam experiment was carried out to study the performance of ^natGd₂O₃-n MCP doped with 3%mol of substrate was studied,The neutron detector was formed by stacking n MCP and traditional MCP back-to-back to explore a set of effective detector installation methods.Finally,the design reference was proposed for the improvement of the vacuum cavity of the detector.In terms of n MCP detector performance,the characteristics of typical neutron and gamma signals are obtained experimentally.For the output charge of the neutron signal at about 170 fc,the rise time of the signal is about 4 ns,the fall time is about 16 ns,and the characteristic width of the signal is about 20 ns.For gamma signal,the output charge is about 140 fc,the rise time of the signal is about 40 ns,the fall time is about 100 ns,and the characteristic width of the signal is about 140 ns.According to the signal characteristics,on the one hand,it is found that the signal amplitude difference between the two signals is not big,therefore,it is difficult to realize the scheme of neutron gamma screening by signal amplitude.As for the study of neutron detection efficiency,the experimental was carried out on the 20 beamline of China Spallation Neutron Source,and neutron detection efficiencies of 35%@2.9（?）and 40%@4.8（?）were obtained.Finally,the topmetal-II chip and readout electronics provided by Central China Normal University were preliminarily tested by GEM detector.The results show that the channel structure of the GEM film can be distinguished,and it has relatively good spatial resolution.The performance of ALD-¹⁰B-n MCP based on atomic layer deposition technology was simulated.Geant4 and mathematical modeling were performed to optimize the pore diameter,wall thickness,bias angle and coating thickness of n MCP.It was shown that the thermal neutron detection efficiency was about 56%and the spatial resolution was about 22μm when the pore diameter was 10μm,the wall thickness was 1μm,the bias angle was 3°and the coating thickness of 1μm.At the same time,through empirical formula calculation,reasonable increase of MCP-Andoe voltage and decrease of the distance between them have positive significance for reducing the diffusion radius of electron cloud and improving spatial resolution.The work of this study lays a foundation for further research on neutron sensitive microchannel plate,including detection efficiency,spatial resolution and optimization of vacuum system,which has an important reference significance.