Radiation-induced modifications in copper oxide growth

Abstract

Radiation-induced effects and their influence on oxidation processes were evaluated for their use as a forensic tool for special nuclear material (SNM). A beam of 10 MeV Au 3+ ions was used to mimic the accumulation of microstructural damage from selfirradiation through the decay of radionuclides. Several copper samples were irradiated as suitable surrogate materials at 200 °C with a flux of 1x10 12 ions/cm•s to damage levels of 5, 10, and 15 displacements per atom (dpa). This corresponds to about 50, 100, and 150 years, respectively, of accumulated a-decay damage in a PuGa alloy assuming a damage rate of 0.1 dpa/year. After irradiation, all samples were exposed to an accelerated aging process induced by thermal treatment at 350 °C for 1 hour in air. This resulted in the growth of a mixed oxide layer (Cu 2 O and CuO) which was characterized in detail using several complementary analytical techniques: Scanning Electron Microscopy, Raman spectroscopy, Synchrotron X-ray diffraction (transmission mode), and Grazing Incidence X-ray diffraction. The oxide layer growth of irradiated Cu at 350°C is distinctly modified as a result of the ion irradiation. Most notably, the growth of the CuO phase is suppressed with increasing radiation damage on the Cu substrate, and structural changes occurred in the Cu 2 O phase. These results indicate that damage from self-irradiation over time can cause quantifiable modifications in the oxidation process of metals that could be harnessed for their use as a novel forensic tool. INTRODUCTION: Special nuclear material (SMN) is defined as Pu, U-233, and U-235-not including the source material per the Atomic Energy Act of 1954. When formula quantity-the amount of material required to achieve criticality-of these radionuclides accumulate, it is then referred to as strategic special nuclear material (SSNM) [Atomic Energy Act of 1954 (P.L. 83-703)]. The control of SNM and SSNM is crucial to national security as these materials can be utilized in nuclear explosives; thus, it is of supreme importance that these materials be monitored, studied, and documented for (i) facility accountability and (ii) nuclear forensics and recovery in the event of their diversion from a nuclear facility. Both physical and chemical properties of SNM/SSNM evolve over time due to the decay and transmutation of radionuclides as well as the accumulated damage from self-irradiation [REF]. These changes occur gradualy with time and can be correlated with the age of the material for forensic purposes [REF]. For example, radiochronometry utilizes mass spectroscopy to determine the chemical compositions and ratio of radioisotopes as a measure of the time that has passed since material fabrication [REF]. Decay counting techniques based on alpha or gamma emission are sometimes employed to identify specific radionuclides that have formed in a given material. Many material identification techniques are currently used for SNM/SSNM, but some are destructive, require large sample quantities (>20g) {REF}, or only apply to certain ra...