Research On A Microchannel Plate Used For Thermal Neutron Imaging

As an important nondestructive testing technique,neutron radiography has many special advantages over X-ray radiography and has been applied to many areas,ranging from the inspection of turbine blades of aircraft engines to the visualization of two phase flow of operating proton exchange membrane fuel cells.Therefore,neutron radiography has much value.Due to good spatial resolution and high neutron detection efficiency,neutron sensitive microchannel plate(nMCP)and neutron imaging detectors based on nMCP have played an important role among various neutron imaging facilities.nMCP has been applied to many areas such as dynamic neutron radiography,energy resolved imaging and neutron resonance imaging.Therefore,research on nMCP is very meaningful to conduct high-quality neutron imaging.This study is based on 106 mm diameter neutron sensitive microchannel plates(nMCPs)doped with 3 mol % natGd2O3.Neutron imaging detectors have been developed using neutron sensitive and normal MCPs.Vacuum level of ~10-11 atm has been achieved and a series of effective detector assembling methods have been developed.New detector chamber and nMCP fixtures have been designed,which will make the assembling process more convenient and the weight of the detector chamber much lighter.In the neutron detection efficiency research,neutron absorption efficiencies and neutron detection efficiencies have been studied by MonteCarlo simulations.Detection efficiency measurements were conducted at the CPHS of Tsinghua University,tests show the detection efficiency @25.3 meV thermal neutron is 34%,which is currently the highest for the neutron sensitive microchannel plate detectors worldwide.In the spatial resolution research,neutron absorption positions and neutron spatial resolution for the nMCP-MCP assembly have been studied by Monte Carlo simulations.Readout methods based on Wedge-and-Strip anode(WSA)and delay line anode have been studied,the spatial resolution of the large area WSA has been tested.Analysis shows the spatial resolution of the WSA is proportional to the cube of anode's diameter.Delay line readout was then used,spatial resolutions and rate capabilities for low energy X-rays and thermal neutrons were studied.Factors affecting the spatial resolution have been studied,including the bias voltage of the MCP V-stack,the readout distance and the readout voltage.Spatial resolution of 65 microns with 15 kV X-rays and 88 microns with thermal neutrons have been achieved,with a rate capability higher than 100 kcps and an imaging area of 8012mm2,which is the biggest fornMCP detectorsworldwide.This study lays foundations and has much significance for further studies on larger area nMCP imaging,including using new readout methods,optimizing the vacuum chamber and the manufacture of larger area nMCPs and MCPs.