Production of Neptunium-236 and Plutonium-236

Study on the production of Neptunium-236 and Plutonium-236 via nuclear reactions using uranium and plutonium isotopes. Research focuses on measurement techniques, stockpile limitations, and future prospects.

• Neptunium
• Plutonium
• Nuclear Science
• Isotope Dilution
• Mass Spectrometry

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1. 236Np/236Pu production via the 235U(d,n) and 238U(p,3n) channels Lee Bernstein Michael Fassbender Nuclear Science Division Lawrence Berkeley National Laboratory Chemistry Division Los Alamos National Laboratory Department of Nuclear Engineering University of California, Berkeley Lee Bernstein WANDA 2020 1 1

2. Isotope Dilution Mass Spectrometry: Standard Reference Material 236Np Neptunium-236g (t1/2=1.5X105 a) is used for IDMS determination of 237Np (t1/2=2.14X106 a). It is neither anthropogenic nor primordial in occurrence and can thus function as an isotope dilution tracer. Current world-wide 236Np stockpile limited to 10 s of g of material. U.S. interagency Np working group* (currently 10 members) formed in August 2015 to coordinate Np production R&D and address metrology community needs and purity requirements. opportunities in the physical sciences and engineering [..] where a shortage [..] is a challenge 236Np is on the DHS High Priority List for future funding. Data for production is extremely sparse! 237Np co-production has to be minimal! 236Np is an NSAC-I (2015) recommended isotope associated with research *SM Jerome, K Carney, R Essex, ME Fassbender, S Goldberg, M Kinlaw, SP LaMont, D Mackney, JJ Morrison, FM Nortier, Reference materials for neptunium determination, Applied Radiation and Isotopes, 126 (2017) 44-48. Lee Bernstein WANDA 2020 2 2

3. Measurements at the LBNL 88-Inch cyclotron: thick-target 235U(d,n)236mNp and thin target 238U(p,3n)236mNp cross sections Stacked Target Holder Beam profile measured Using GAFChromic film Deuterons @ 12, 16 MeV, Protons @ 27 MeV HPGe counter The 235U sample was overfilled with beam Lee Bernstein WANDA 2020 3 3

4. Post-irradiation counting shows the 642.3 keV -ray from the decay of the 236mNp isomeric state (t =22.5 h) 159.4(52) fg 236mNp 89.98(20) fg/uAh mg 554(21) fg 236mNp 9.265(3) fg/uAh mg From 240Pu 642 keV Multiple channels observed via -spec *Nucl. Phys. A 135 p 36-48 (1969) Lee Bernstein WANDA 2020 4 4

5. Quantification of 236gNp / 237Np at LANL ICP-MS data for (d,n) following U separation Quantification of 236gNp / 237Np production requires chemical workup and ICP-MS based analysis, due to lifetimes (t1/2=1.5x105 y, 2.14x106 y, respectively). The 200 mg 93% 235U samples irradiated with 12 and 16 MeV deuterons underwent analysis at LANL in Spring 2019. 7.25(15)pg/uA for 16 MeV. 6.85(11)pg/uA for 12 MeV 1.05(38) for 16 MeV 1.55(18) for 12 MeV. No 236U produced! Stay tuned 235U (93% of target) 236U 236gNp production rates: 236Np:237Np production ratio (atom basis): LANL -spect results 236Pu from 236mNp observed via -spec 238U(p,3n) targets awaiting ICP-MS Lee Bernstein WANDA 2020 5 5

6. Next Steps Goals met so far: Irradiation and gamma-spectroscopy at LBNL Chemical analysis at LANL Significant quantities of 237Np observed in the deuteron-irradiated targets ~60% present in un-irradiated targets due to pedigree Remainder co-produced as contaminant from 238U(d,3n) reactions Further characterization of the 235U(d,n)236Np channel s production potential will require higher-purity 235U targets 99.4% enrichment targets are currently in fabrication at LLNL (Narek Gharibyan), with a stack irradiation planned for June 2020 Target Beam Energy 236mNp ( -spec) Scheduled for June 7-9, 2020 236gNp (ICP-MS) 236Pu ( -spec) 235U (93%) D D p 12 MeV 16 MeV 16-25 MeV 235U (93%) natU 235U (99.4%) D 14 MeV Lee Bernstein WANDA 2020 6 6

7. Collaborators Andrew Voyles2, Lee Bernstein1,2, Michael Fassbender3, M.S. Basunia1, Jon Batchelder1, Andrew Gaunt3, Susan Hanson3, Ian Kolaja1, Jon Morrell1, Iain May3, N. Pettersen4, Melinda Wren3 1University of California Berkeley Department of Nuclear Engineering 2Lawrence Berkeley National Laboratory 3Los Alamos National Laboratory 4University of Oslo This work has been performed under the auspices of the U.S. Department of Energy by Lawrence Berkeley National Laboratory under contract No. DE-AC02- 05CH11231. This research is also supported by the U.S. Department of Energy Isotope Program, managed by the Office of Science for Nuclear Physics and the US Nuclear Data Program (Grant FOA LAB 17-1763). Lee Bernstein WANDA 2020 7 7