Abstract
Energy-resolved neutron imaging enables non-destructive analyses of bulk structure and elemental composition, which can be resolved with high spatial resolution at bright pulsed spallation neutron sources due to recent developments and improvements of neutron counting detectors. This technique, suitable for many applications, is demonstrated here with a specific study of ~5–10 mm thick natural gold samples. Through the analysis of neutron absorption resonances the spatial distribution of palladium (with average elemental concentration of ~0.4 atom% and ~5 atom%) is mapped within the gold samples. At the same time, the analysis of coherent neutron scattering in the thermal and cold energy regimes reveals which samples have a single-crystalline bulk structure through the entire sample volume. A spatially resolved analysis is possible because neutron transmission spectra are measured simultaneously on each detector pixel in the epithermal, thermal and cold energy ranges. With a pixel size of 55 μm and a detector-area of 512 by 512 pixels, a total of 262,144 neutron transmission spectra are measured concurrently. The results of our experiments indicate that high resolution energy-resolved neutron imaging is a very attractive analytical technique in cases where other conventional non-destructive methods are ineffective due to sample opacity.
Highlights
The results of this study demonstrate the unique capabilities of energy-resolved neutron transmission and diffraction imaging for the non-destructive study of nearly cm-thick natural gold samples, which are opaque in conventional X-ray methods
The transmission spectra measured for the 4 gold samples are shown in Fig. 3 together with the transmission calculated from tabulated cross sections (ENDF database21)
The present study is limited to reconstruction of the elemental composition from the neutron transmission spectra measured at room temperature
Summary
Recent developments of high resolution neutron counting detectors combined with bright pulsed neutron sources enable high resolution energy-resolved neutron imaging with mm-scale[10] and even sub-100 μm spatial resolution[11,12]. This new generation of neutron imaging detectors can register neutrons with 10–500 ns timing resolution (varied with the neutron energy), providing the possibility to measure neutron transmission simultaneously over a wide range of energies, from epithermal keV-energy neutrons to cold ~meV neutrons, spanning six orders of magnitude in neutron energy and the corresponding changes in neutron attenuation due to different interaction mechanisms in a single experiment.
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