A) Micro-channel plate B) Parallel micro-pillar 2D array C) Oblique micro-pillar 2D array. Credit: Science China PressTo increase the neutron detection efficiency of bulk-micromegas (MICRO-MEsh GAseous Structure) neutron detectors, researchers from Lanzhou University in China and the University of Tennessee-Knoxville have proposed three new types of thin-film converters: micro-channel, parallel micro-pillar, and oblique micro-pillar 2D array. When validated using Monte Carlo simulations, the latter design showed a threefold increase in neutron detection efficiencies.

The team has now made a bulk-micromegas based neutron imaging detector with a traditional thin-film neutron converter. The dimensions of the detector's sensitive area are 57.4 mm × 88.6 mm, which is composed of 1,728 rectangular pads (36 pads in the X direction and 48 pads in the Y direction). Each pad has an area of 1.50 mm × 1.75 mm.

Although the detector has a relatively low neutron detection efficiency, very good mask images are obtained. Without any modification, the detector can be used as a 2D neutron beam monitor for projects that require low detection efficiency (detectors with high detection efficiency cannot operate with high intensity neutron beams). At the IEEE Nuclear Science Symposium and Medical Imaging Conference, CA, USA (2012), Dr. Xiaodong Zhang presented this work on behalf of the FNI collaboration.

The team is currently collaborating with companies to make detectors using micro-machining and new printed circuit board techniques.

Additionally, the novel detectors can be used to improve thermal neutron, cold neutron and ultra-cold neutron efficiencies, through simply changing the detection conversion material from polyethylene to boron-10, or lithium-7. Zhang is optimistic about the impact of these detectors in different research fields: "By choosing different conversion materials I envisage that at least a 10% detection efficiency can be achieved for thermal neutron detection. Our detectors can be used to replace the current neutron detectors which use helium-3, and hence reduce the demand for helium-3."

Currently, his team is developing this technique at Spallation Neutron Source in Oak Ridge National Laboratory.

Development of Fast Neutron Imaging Detector based on Mini-Micromegas TPC

Optimization of neutron convertor inside Bulk-Micromegas based fast neutron imaging system with Geant4 simulation

Source: Science China Press Co., Ltd.