A Micro Pixel Chamber Based Neutron Imaging Detector with Boron Converter for Energy-Resolved Neutron Imaging at J-PARC

Energy-resolved neutron imaging at a pulsed source utilizes the energy-dependent neutron transmission, measured via time-of-flight, to extract quantitative information on the internal microstructure of an object in situ. These techniques, however, are currently limited by the count-rate capability of available imaging detector systems, resulting in long measurement times and reduced spatial resolution. At RADEN, we are building on our previous detector development work to provide nearly three times improvement in rate performance of our micro-pixel chamber based neutron imaging detector $(_{\mu }$ NID) by changing from 3 He to a boron-based neutron converter and optimizing the shape for a much reduced event size and maximized detection efficiency. We are also designing a new micro-pattern readout element with an additional readout axis to facilitate clean event separation under high-rate conditions. Proof-of-principle testing at RADEN of the $_{\mu }$ NID with a flat, $1.2{\mu }m$ thick $^{10}B$ conversion layer confirmed a spatial resolution of 0.45 to 0.5 mm and indicated an improvement in rate capacity up to 22 Mcps or more. Once the boron converter is optimized for detection efficiency, this detector will help to unlock the full potential of these energyresolved neutron imaging techniques at pulsed sources.