Thermal signatures of Cu metal revealed through oxygen isotope fractionation
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Thermal signatures of Cu metal revealed through oxygen isotope fractionation Jessica L. Bishop1,4 · Ryan Unger1 · Anthony M. Faiia2 · Anna Szynkiewicz2 · John D. Auxier II4 · Howard L. Hall1,2,3 · Maik Lang1 Received: 11 June 2020 / Accepted: 9 October 2020 / Published online: 29 October 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract Cu metal, surrogate for metallic actinide materials, was subject to accelerated aging through thermal treatment. A multiphase oxide-layer (Cu2O, CuO) was detected, varying with temperature (250–400 °C) and aging time (1–3.5 h). Isotope ratio mass spectrometry revealed temperature-dependent isotopic fractionation of O, evidenced by the enrichment of Cu oxide in 16O isotopes with increasing temperature. Isotopic fractionation occurred initially with atmospheric O, and later through exchange with water vapor. Raman spectra contributed insight on phase fraction and local bonding of Cu oxides. O isotopes could serve as a useful tracer for studying oxide layer growth from aging metallic systems. Keywords Oxygen · Isotopic fractionation · Raman spectroscopy · Copper · Plutonium · Nuclear forensics · Oxidation · CuO · Cu2O
Introduction There is a critical need in nuclear forensics for a novel technique able to rapidly and effectively characterize intercepted special nuclear material (SNM) [1]. Pu based materials, a component of SNM, is routinely exposed to high temperature (> 200 °C) in a variety of manufacturing processes triggering oxidation as well as constant radiation damage from internal alpha decay from select Pu isotopes (Pu-238, Pu-239, Pu-240) generating defects in the crystal structure [2]. The complex transformation in structure, isotopic abundance, and purity of these materials often complicates the ability to chemically characterize them. Typically, forms of radiochronometry are employed to ratio fission products of decaying Pu isotopes. However, * Maik Lang [email protected] 1
Department of Nuclear Engineering, University of Tennessee, Knoxville, USA
2
Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, USA
3
Institute for Nuclear Security, University of Tennessee, Knoxville, TN 37996, USA
4
Chemistry Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
some of these types of analysis are destructive—requiring chemical digestion of the material for measurement using a mass spectrometer, most commonly Secondary Ion Mass Spectrometry (SIMS), Thermal Ionization Mass Spectrometry (TIMS), and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Previous O isotope studies on U-based material utilizing TIMS specifically was proven to be an effect method to investigate origin of U-based material [3]. This study expands on the use of O-isotopes as a tracer for possible origin as well as thermal history by utilizing a unique set of investigative techniques—Raman Spectroscopy complementary to Isotope Ratio Mass Spectroscopy (IRMS). It is imperative that the analysis of these materials is quick to minimize exposure, whi
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