Non-Destructive Study of Bulk Crystallinity and Elemental Composition of Natural Gold Single Crystal Samples by Energy-Resolved Neutron Imaging

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.

Neutron microtomography of voids in gold

“…Imaging with neutrons has been utilized for number of niche applications in which imaging with other types of radiation (such as X-rays) provides less convenient probe. One such example of niche application is imaging of microstructure of some very high atomic number materials [1] , [2] , [3] , in which radiation in (hard) X-ray regime does not provide sufficient transmission signal to reveal the inner structure of such materials. The different contrast mechanisms of neutrons with matter (to that of X-rays) allow for investigation of materials based on high atomic number elements.…”

Neutron Imaging at LANSCE—From Cold to Ultrafast

“…The results of these efforts are reported in several publications [55][56][57]. Furthermore, the unique capabilities of energy-resolved neutron imaging for single crystal characterization were applied to characterize natural gold single crystals [58]. In an effort partially supported by the New Mexico Consortium and DOE/NNSA science campaigns, LANL was able to characterize fossilized skulls with both neutron and hard X-ray CT.…”

Asic developments for radiation imaging applications: The medipix and timepix family

“…The MCP can be doped with a neutron absorber such as Boron for direct neutron imaging [89], providing unique contrast in neutron imaging experiments where other conventional methods fail due to sample opacity e.g. High-Z materials such as nuclear fuels, [90], inclusions of Pd within natural gold single crystals, [91] or have low contrast (e.g. hydrogenous substance such as oil imaged within shale samples).…”