AMS measurements of Zr-93 for astrophysical and nuclear technology applications

Dr Stefan Pavetich1, Anton Wallner1,2, Keith Fifield1, Michaela B Froehlich1, Shlomi Halfon3, Yanan Huang4, Dominik Koll1, Martin Martschini5, Michael Paul6, Zuzana Slavkovská1, Asher Shor3, Johannes H Sterba7, Moshe Tessler6, Steve G Tims1, Leo Weissman3

1Research School of Physics, The Australian National University, , Australia, 2Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany, 3Soreq Nuclear Research Center, Yavne, Israel, 4School of Marine Sciences, Sun Yat-sen University, Zhuhai, China, 5University of Vienna, Faculty of Physics, VERA Laboratory, Vienna, Austria, 6Racah Institute of Physics, Hebrew University, Jerusalem, Israel, 7TRIGA Center Atominstitut, Technische Universität Wien, Vienna, Austria

The radionuclide ⁹³Zr with a half-life of (1.61±0.05) Myr [1] plays an important part in stellar nucleosynthesis and nuclear technology. In stellar environments it is predominately produced by neutron capture on stable ⁹²Zr in the slow neutron capture process (s-process). Neutron capture cross sections in the keV range are the key parameters to model this process. They are of particular importance in the Zr-mass range as this is the transition area between two components of the s-process taking place in two different stellar environments. Back on Earth, ⁹³Zr is produced in significant amounts in reactors as a high yield fission product of the nuclear fuel and by neutron capture on stable ⁹²Zr, which is used in the cladding of nuclear fuel rods.

Despite their importance, experimental data on neutron capture cross sections of ⁹²Zr at thermal, epithermal, and stellar energies, suffer from large uncertainties. The combination of neutron activations and AMS presents an alternative method to online time-of-flight (TOF) measurements for the determination of these cross sections. The main challenges in AMS of ⁹³Zr are the interference from the stable isobar ⁹³Nb and the production of reference material. The high particle energies available at the Heavy Ion Accelerator Facility (HIAF) are ideal to tackle the first challenge. Additionally, by using ZrF₄ as sample material and extracting ZrF₅-, the Nb background is reduced by ≃2 orders of magnitude compared to the use of ZrO₂ samples and extraction of ZrO- beams. Using the 13+ charge state and particle energies of ≃190 MeV ⁹³Zr/Zr background levels in the 10-¹² range are regularly achieved at HIAF.

Zirconium oxide powders were irradiated at the reactor of the Atominstitut in Vienna with thermal and epithermal neutrons, and a ZrO₂ pellet was irradiated at the Soreq Applied Research Accelerator Facility with keV neutrons produced by the ⁷Li(p,n) reaction on the Liquid-Lithium Target. These samples were converted into ZrF₄ and their ⁹³Zr content was measured at HIAF. Preliminary results for the cross sections seem significantly higher than the most recent values from literature [2,3] (TOF and compilation respectively) but they still suffer from a large uncertainty in the nominal ratio of the AMS reference material that was used. Currently a new more precise reference material, produced via fission of ²³⁵U, is being characterised.

[1] C. M. Baglin, Nucl. Data Sheets 112, 1163 (2011).
[2] G. Tagliente et al., Phys. Rev. C 81, 055801 (2010).
[3] S.F. Mughabghab, Atlas of Neutron Resonances (2018).


Biography:

Stefan Pavetich studied Physics at the University of Vienna. He received his PhD in Physics from the Technical University of Dresden in 2015. His PhD work focused on ion source development for AMS and was conducted at the Helmholtz-Zentrum Dresden-Rossendorf. Currently, he is a Postdoctoral Fellow in the Department of Nuclear Physics at the ANU investigating neutron -, and alpha capture reactions relevant for nucleosynthesis in stellar environments and developing AMS for non-routine radionuclides (Zr-93, Fe-60). He participated in interdisciplinary studies using AMS, including reconstruction of irradiation histories of meteorites and groundwater modelling in arid regions in Israel and Oman.

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Date

Nov 19 2021

Time

FRIDAY
8:45 am - 9:45 am