Abstract
The energy-dependence of the neutron cross section provides vastly different contrast mechanisms than polychromatic neutron radiography if neutron energies can be selected for imaging applications. In recent years, energy-resolved neutron imaging (ERNI) with epi-thermal neutrons, utilizing neutron absorption resonances for contrast as well as for quantitative density measurements, was pioneered at the Flight Path 5 beam line at LANSCE and continues to be refined. Here we present event centroiding, i.e., the determination of the center-of-gravity of a detection event on an imaging detector to allow sub-pixel spatial resolution and apply it to the many frames collected for energy-resolved neutron imaging at a pulsed neutron source. While event centroiding was demonstrated at thermal neutron sources, it has not been applied to energy-resolved neutron imaging, where the energy resolution requires to be preserved, and we present a quantification of the possible resolution as a function of neutron energy. For the 55 μm pixel size of the detector used for this study, we found a resolution improvement from ~80 μm to ~22 μm using pixel centroiding while fully preserving the energy resolution.
Highlights
Material characterization by radiographic methods is driven by the contrast mechanism of the probing radiation with the sample
While X-rays interact with the electronic shell of the nuclei and provide contrast approximately proportional to the gravimetric density of a sample, neutrons interact with the nuclei and the imaging contrast has no correlation with the atomic number, but varies for thermal neutrons over orders of magnitude in cross section from isotope to isotope
Applying centroiding improves overall butOne is limited would be to increase the number of iterations for each image, but the centroiding pattern by solution the incident neutron flux and in the case of microchannel plate (MCP) detectors, by the channel size
Summary
Material characterization by radiographic methods is driven by the contrast mechanism of the probing radiation with the sample. While X-rays interact with the electronic shell of the nuclei and provide contrast approximately proportional to the gravimetric density of a sample, neutrons interact with the nuclei and the imaging contrast has no correlation with the atomic number, but varies for thermal neutrons over orders of magnitude in cross section from isotope to isotope. This is applied routinely as an imaging modality at neutron facilities worldwide [1,2,3,4]. By measuring full transmission spectra, i.e., with the ability to record thousands of TOF channels in each pixel as provided by modern neutron imaging detectors [8,9,10] installed at modern intense pulsed neutron sources [11,12,13,14,15], data analysis codes such as Oak Ridge National Lab’s SAMMY [16]
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