Understanding neutron capture processes in uranium deposits using combined U-Sm-Nd isotopic compositions

Journal Article · Mon Jul 28 00:00:00 EDT 2025 · Applied Geochemistry

DOI:https://doi.org/10.1016/j.apgeochem.2025.106514· OSTI ID:2585270

Shollenberger, Quinn R. ^[1]; Render, Jan ^[1]; Murphy, Melissa J. ^[2]; Brennecka, Gregory A. ^[1]

---

1. University of Münster (Germany); Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
2. Mel Murphy Geochemistry, Copenhagen (Denmark)

Valuable insights into the history and evolution of a geologic deposit can be found by investigating neutron capture reactions. Thermal neutron capture reactions occur within both the samarium (Sm) and the uranium (U) systems, where ¹⁴⁹Sm and ²³⁵U can capture neutrons to become ¹⁵⁰Sm and ²³⁶U, respectively. Although largely unexplored, paired measurements of ¹⁵⁰Sm and ²³⁶U could be important for understanding neutron capture effects within uranium ore bodies, and such measurements are potentially useful in nuclear forensics for assessing a material's provenance or mineral exploration. In this work, we refined measurement procedures of Sm isotope compositions utilizing MC-ICPMS. While geologic reference materials were found to have indistinguishable Sm isotope compositions, we found significant isotope variations consistent with nuclear field shift among synthetic Sm standards. Here, this observation highlights that future high-precision Sm isotope investigations need to carefully evaluate synthetic standard(s) against geologic reference materials until an unfractionated and agreed-upon standard is identified. Here, we applied this method to a set of nine uranium ores from the South Australian Beverley North uranium deposits. Although ²³⁶U excesses had been previously reported for these U ores, we found no measurable isotopic shifts in ¹⁴⁹Sm-¹⁵⁰Sm at the current level of precision (±5 parts per million). One possible explanation for this disparity in the observed neutron capture signatures between U and Sm is that the source(s) of the U and Sm in these ores may be decoupled. This is consistent with the finding that these ores have variable ¹⁴³Nd/¹⁴⁴Nd, thus demonstrating that diverse sources were involved in the formation of the Beverley North deposits. Alternatively, this deposit may be too young (<50Ma) to have accumulated measurable neutron capture effects in Sm to be detected with the methods employed here.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC52-07NA27344
• OSTI ID: 2585270
• Report Number(s): LLNL--JRNL-2000907
• Journal Information: Applied Geochemistry, Journal Name: Applied Geochemistry Journal Issue: 191 Vol. 191; ISSN 0883-2927
• Publisher: Elsevier BV
• Country of Publication: United States
• Language: English

Related Subjects

Mineral exploration
Neodymium isotopes
Nuclear field shift
Samarium isotopes
Uranium ore
Uranium-236