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Applications of accelerator mass spectrometry in nuclear verification
(Institute of Nuclear Materials Management, 2012-07-01) Hotchkis, MAC; Child, DP; Wilcken, K
The reduction and eventual elimination of nuclear threats to global peace and security remains a high priority for governments around the world. The approach towards this goal involves multiple paths, including through existing treaties, such as the Non-proliferation Treaty (NPT), through bringing into force treaties and agreements such as the Additional Protocol and the Comprehensive Test Ban Treaty, and through the negotiation and enactment of new arms reduction measures and treaties such as the Fissile Material Cut-off Treaty. The long-lived actinides radioisotopes of interest are usually the most abundant species of that mass and radiochemical separation is sufficient to remove atomic isobars if they are present. The key advantage of accelerator mass spectrometry (AMS), compared to other forms of mass spectrometry, is its exceptional abundance sensitivity.
Global fossil methane emissions constrained by multi-isotopic atmospheric methane histories.
(American Geophysical Union, 2025-02-28) Fujita, T; Graven, H; Zazzeri, G; Hmiel, B; Petrenko, VV; Smith, AM; Michel, SE; Morimoto, S
The global CH4 budget of sources and sinks is highly uncertain, particularly the emissions from specific sources such as fossil fuels (FF) or agriculture. Here, we estimate plausible global CH4 source and sink scenarios using historical observations and simulations of atmospheric CH4 mole fraction and its stable isotopic (δ13C-CH4, δD-CH4) and radiocarbon (Δ14C-CH4) composition, combining constraints from all these tracers for the first time. We employ a one-box model along with a Monte Carlo particle filter technique, explicitly exploring the impact of each isotopic constraints and uncertainties in prior CH4 source and sink parameters on posterior sectorial source fractions. We find our posterior anthropogenic FF emissions at the global scale are 30% lower than previous isotope-based studies. Our analysis suggests previous δ13C-CH4-based studies are potentially biased because the current database-derived estimate of the global mean biogenic δ13C-CH4 source signature is too low and/or current sink-weighted total carbon kinetic isotope effect is underestimated. We find modern atmospheric Δ14C-CH4 data constrains lower global FF emissions after 1980s, which is contrary to the most recent finding that utilized atmospheric Δ14C-CH4 data, but supported by an independent estimate of global nuclear 14CH4 emissions. Our multi-isotopic constraints align with CH4-only inversion results, while reducing their uncertainties with greater robustness against different prior emission scenarios. We find strong constraints not only on FF emissions but also other key sources and sinks, showing that long-term multi-isotopic observations are critical for refining the global CH4 budget and developing effective CH4 emission mitigation strategies. © 2025. The Author(s). This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Universality of time–temperature scaling observed by neutron spectroscopy on bottlebrush polymers
(American Chemical Society, 2021-05-14) Bichler, KJ; Jakobi, B; Sakai, VG; Klapproth, A; Mole, RA; Schneider, GJ
The understanding of materials requires access to the dynamics over many orders of magnitude in time; however, single analytical techniques are restricted in their respective time ranges. Assuming a functional relationship between time and temperature is one viable tool to overcome these limits. Despite its frequent usage, a breakdown of this assertion at the glass-transition temperature is common. Here, we take advantage of time- and length-scale information in neutron spectroscopy to show that the separation of different processes is the minimum requirement toward a more universal picture at, and even below, the glass transition for our systems. This is illustrated by constructing the full proton mean-square displacement for three bottlebrush polymers from femto- to nanoseconds, with simultaneous information on the partial contributions from segmental relaxation, methyl group rotation, and vibrations. The information can be used for a better analysis of results from numerous techniques and samples, improving the overall understanding of materials properties. © 2021 The Authors. Published by American Chemical Society. Open Access CC-BY-4.0.
Elemental mapping in a preclinical animal model reveals white matter copper elevation in the acute phase of central nervous system trauma
(American Chemical Society, 2023-09-11) Evans, CW; Egid, A; Mamsa, SSA; Paterson, DJ; Ho, D; Bartlett, CA; Fehily, B; Lins, BR; Fitzgerald, M; Hackett, MJ; Smith, NM
Understanding the chemical events following trauma to the central nervous system could assist in identifying causative mechanisms and potential interventions to protect neural tissue. Here, we apply a partial optic nerve transection model of injury in rats and use synchrotron X-ray fluorescence microscopy (XFM) to perform elemental mapping of metals (K, Ca, Fe, Cu, Zn) and other related elements (P, S, Cl) in white matter tracts. The partial optic nerve injury model and spatial precision of microscopy allow us to obtain previously unattained resolution in mapping elemental changes in response to a primary injury and subsequent secondary effects. We observed significant elevation of Cu levels at multiple time points following the injury, both at the primary injury site and in neural tissue near the injury site vulnerable to secondary damage, as well as significant changes in Cl, K, P, S, and Ca. Our results suggest widespread metal dyshomeostasis in response to central nervous system trauma and that altered Cu homeostasis may be a specific secondary event in response to white matter injury. The findings highlight metal homeostasis as a potential point of intervention in limiting damage following nervous system injury. © 2023 American Chemical Society.
Synchrotron CT of an equine digit at the Australian Synchrotron imaging and medical beamline
(International Union of Crystallography, 2021-11) Montgomery, JB; Klein, M; Boire, JR; Beck, C; Häusermann, D; Maksimenko, A; Hall, CJ
Laminitis is an extremely painful and debilitating condition of horses that can affect their athletic ability and even quality of life. The current gold standard for assessment of laminar tissue is histology, which is the only modality that enables detailed visualization of the lamina. Histology requires dissection of the hoof and therefore can only represent one specific time point. The superior spatial and contrast resolution of synchrotron computed tomography (sCT), when compared with readily available imaging modalities, such as radiographs and conventional CT, provides an opportunity for detailed studies of the lamina without the need for hoof dissection and histological assessment. If the resolution of histology can be matched or even approached, dynamic events, such as laminar blood flow, could also be studied on the microscopic tissue level. To investigate this possible application of sCT further, two objectives are presented: (i) to develop a protocol for sCT of an equine digit using cadaver limbs and (ii) to apply the imaging protocol established during (i) for sCT imaging of the vasculature within the foot using an ex vivo perfusion system to deliver the vascular contrast. The hypotheses were that sCT would allow sufficient resolution for detailed visualization to the level of the secondary lamellae and associated capillaries within the equine digit. Synchrotron CT enabled good visualization of the primary lamellae (average length 3.6 mm) and the ex vivo perfusion system was able to deliver vascular contrast agent to the vessels of the lamina. The individual secondary lamellae (average length 0.142 mm) could not be seen in detail, although differentiation between primary and secondary lamellae was achieved. This approaches, but does not yet reach, the current gold standard, histology, for assessment of the lamellae; however, with further refinement of this imaging technique, improved resolution may be accomplished in future studies. © 2021 The Authors - Open Access CC BY.

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