arXiv subjects

Estrid Buhl Naver

Publications and source records attributed to Estrid Buhl Naver.

3 recordsLinked to original sources

arXiv2026

Direct detection of hydrogen reveals a new macroscopic crustal water reservoir on early Mars

The next great leap in Martian exploration will be the return of samples to Earth. To ensure the maximum scientific return from studying these samples, the development and utilisation of nondestructive analytical techniques are essential to enable early three-dimensional characterisation of their interiors. Neutron computed tomography is a powerful method in this context: it is highly sensitive to hydrogen and complements the more conventional X-ray computed tomography. Because the distribution and nature of hydrous phases are central to understanding the habitability, the climatic and geological evolution, and potential biosignatures of Mars, identifying hydrogenbearing phases in Martian crustal rocks is of particular importance. Using the only Martian crustal material available on Earth, the NWA 7034 meteorite and its pairs, we show that combined neutron and X-ray computed tomography enables non-destructive sample-wide mapping of hydrogen and reveals the distribution and petrographic contexts of hydrous phases. We identify hydrogen-rich iron oxyhydroxides within ancient igneous clasts, forming a macroscopic mineralogical water reservoir within the meteorite. These alteration assemblages closely resemble those observed in samples collected by the Perseverance rover in Jezero crater, where hydrated iron oxyhydroxides are also present. This similarity suggests that such phases may represent a widespread near-surface water reservoir on early Mars.

astro-ph.EP↗

arXiv2024

Neutron phase filtering for separating phase- and attenuation signal in aluminium and anodic aluminium oxide

Neutron imaging has gained significant importance as a material characterisation technique and is particularly useful to visualise hydrogenous materials in objects opaque to other radiations. Particular fields of application include investigations of hydrogen in metals as well as metal corrosion, thanks to the fact that neutrons can penetrate metals better than e.g. X-rays and are at the same time highly sensitive to hydrogen. However at interfaces for example those that are prone to corrosion, refraction effects sometimes obscure the attenuation image, which is used to for hydrogen quantification. Refraction, as a differential phase effect, diverts the neutron beam away from the interface in the image which leads to intensity gain and intensity loss regions, which are superimposed to the attenuation image, thus obscuring the interface region and hindering quantitative analyses of e.g. hydrogen content in the vicinity of the interface or in an oxide layer. For corresponding effects in X-ray imaging, a phase filter approach was developed and is generally based on transport-of-intensity considerations. Here, we compare such an approach, that has been adapted to neutrons, with another simulation-based assessment using the ray-tracing software McStas. The latter appears superior and promising for future extensions which enable fitting forward models via simulations in order to separate phase and attenuation effects and thus pave the way for overcoming quantitative limitations at refracting interfaces.

cond-mat.mtrl-sci↗

arXiv2022

Polychromatic neutron phase contrast imaging of weakly absorbing samples enabled by phase retrieval

We demonstrate the use of a phase retrieval technique for propagation-based phase contrast neutron imaging with a polychromatic beam. This enables imaging samples with low absorption contrast and/or improving the signal-to-noise ratio to facilitate e.g. time resolved measurements. A metal sample, designed to be close to a pure phase object, and a bone sample with canals partially filled with D2O were used for demonstrating the technique. These samples were imaged with a polychromatic neutron beam followed by phase retrieval. For both samples the signal-to-noise ratio were significantly improved and in case of the bone sample, the phase retrieval allowed for separation of bone and D2O, which is important for example for in situ flow experiments. The use of deuteration-contrast avoids the use of chemical contrast enhancement and makes neutron imaging an interesting complementary method to X-ray imaging of bone.

physics.med-ph↗