Energy-resolving neutron transmission radiography at the ISIS pulsed spallation source with a high-resolution neutron counting detector

Neutron transmission radiography can be strongly enhanced by adding spectroscopic data spatially correlated with the attenuation coefficient. This can now be achieved at pulsed neutron sources, utilizing a neutron detector with high spatial and temporal resolution. The energy of transmitted neutrons can be recovered from their time-of-flight, simultaneously with the acquisition of the transmission radiographic image by a pixilated detector. From this, the positions of Bragg edges can be obtained for each pixel of the radiographic image. The combination of both spectroscopic and transmission information enables high spatial resolution studies to be carried out on material composition, phase transitions, texture variations, as well as strain analysis, as long as the resolution and statistics are favorable. This paper presents initial results from proof-of-principle experiments on energy-resolved neutron transmission radiography, using a neutron counting detector consisting of neutron-sensitive microchannel plates (MCPs) and a Medipix2 electronic readout. These experiments demonstrate that the position of Bragg edges are measurable with a few mÅ resolution in each 55 μm pixel of the detector, corresponding to ΔE/E ∼ 0.1%. However, the limited intensity of most current neutron sources requires a compromise between the energy resolution and the area over which it was integrated. Still, the latter limitation can be overcome by combining energy information for several neighboring pixels, while transmission radiography can still be done at the limit of the detector spatial resolution.