Abstract
Neutron resonance absorption imaging is a non-destructive technique that can characterize the elemental composition of a sample by measuring nuclear resonances in the spectrum of a transmitted beam. Recent developments in pixelated time-of-flight imaging detectors coupled with pulsed neutron sources pose new opportunities for energy-resolved imaging. In this paper we demonstrate non-contact measurements of the partial pressure of xenon and krypton gases encapsulated in a steel pipe while simultaneously passing the neutron beam through high-Z materials. The configuration was chosen as a proof of principle demonstration of the potential to make non-destructive measurement of gas composition in nuclear fuel rods. The pressure measured from neutron transmission spectra (∼739 ± 98 kPa and ∼751 ± 154 kPa for two Xe resonances) is in relatively good agreement with the pressure value of ∼758 ± 21 kPa measured by a pressure gauge. This type of imaging has been performed previously for solids with a spatial resolution of ∼ 100 μm. In the present study it is demonstrated that the high penetration capability of epithermal neutrons enables quantitative mapping of gases encapsulate within high-Z materials such as steel, tungsten, urania and others. This technique may be beneficial for the non-destructive testing of bulk composition of objects (such as spent nuclear fuel assemblies and others) containing various elements opaque to other more conventional imaging techniques. The ability to image the gaseous substances concealed within solid materials also allows non-destructive leak testing of various containers and ultimately measurement of gas partial pressures with sub-mm spatial resolution.
Highlights
The penetrating capability of neutrons in most materials, coupled with their sensitivity to light atoms such as hydrogen, lithium and boron, make neutron radiography an attractive non-destructive option for the characterization of combinations of substances that include high-Z materials
The energy-resolved neutron imaging technique implemented at spallation neutron sources described in this paper enables simultaneous acquisition of neutron transmission spectra within each pixel of data set in a wide range of neutron energies, spanning from epithermal energies to cold neutrons
These spatially-resolved neutron transmission measurements provide a unique possibility to reconstruct the maps of bulk elemental composition within samples opaque to other more conventional imaging techniques, based on X-ray of electron interrogation
Summary
The penetrating capability of neutrons in most materials, coupled with their sensitivity to light atoms such as hydrogen, lithium and boron, make neutron radiography an attractive non-destructive option for the characterization of combinations of substances that include high-Z materials. Whereas the technique is frequently performed with a white spectrum using a thermal or cold neutron beam[1,2,3] the characterization options are greatly expanded by energy-resolved imaging[4,5,6] in which transmission spectra are measured for each pixel of the image. This allows spatially-resolved imaging of features related to microstructure variation such as texture and mosaicity,[7,8,9,10] residual strain[7,10,11,12,13] and phase distributions,[14] when thermal and cold neutrons are used. Studies that employ resonances appearing in the epithermal range of energies have been reported for the investigation of elemental composition[15,16,17,18,19,20,21] and remote measurement of temperature.[22,23,24]
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