Zr-93 developments at the Heavy Ion Accelerator Facility at ANU

Stefan Pavetich, Alexander Carey, L. K. Fifield, Michaela B. Froehlich, Shlomi Halfon, Angelina Kinast, Martin Martschini, Dominic Nelson, Michael Paul, Asher Shor, Johannes H. Sterba, Moshe Tessler, Stephen G. Tims, Leonid Weissman, Anton Wallner

The long-lived radionuclide Zr-93 t(1/2) = (1.61 +/- 0.05) Ma plays an important role in nuclear astrophysics and nuclear technology. In stellar environments, it is mainly produced by neutron capture on the stable nuclide Zr-92. On Earth high amounts of radioactive 93Zr are produced in nuclear power plants directly from U-235 fission, but also by neutron capture on Zr-92, as Zr-alloys are commonly used as cladding for nuclear fuel rods.

Despite its importance, the neutron capture cross section of Zr-92 at thermal and stellar energies (keV) is not well known. Neutron irradiation of Zr-92 and subsequent determination of produced Zr-93 via AMS is a promising approach to resolve this issue. The main challenge in AMS measurements of Zr-93 is the interference from the stable isobar Nb-93. The high particle energies available with the 14UD tandem accelerator at the Australian National University are ideal to tackle this challenge. Different sample materials, molecular ion species and sample holder materials were tested for their Nb-93 background. Commercial ZrO2 powder irradiated with thermal neutrons from the reactor at the Atominstitut in Vienna (ATI) was used as reference material for AMS measurements. In contrast to literature reports and gamma-activity measurements of Nb-95, which suggest that chemical Nb reduction works, elevated Nb-93 contents were measured in chemically pre-treated samples. The reasons are under investigation. At the ANU we developed AMS for similar to 210 MeV Zr-93 ions using an 8 anode ionisation chamber. We achieved background levels of (93)A/Zr similar to 10(-12) with acceptance of 2-8% of the Zr-93 ions at the high-energy side. This is more than an order of magnitude better than previously reported. The Nb-93 isobar was suppressed by a factor between 13,000 and 90,000 in the detector.

This performance allows measurements of the thermal and stellar neutron-capture cross section of Zr-92 for samples irradiated at the ATI and the Soreq Applied Research Accelerator Facility, respectively, using AMS.

Externe Organisation(en)
Australian National University, Soreq Nucl Res Ctr, Technische Universität München, Hebrew University Jerusalem, Technische Universität Wien
Nuclear Instruments & Methods in Physics Research. Section B. Beam Interactions with Materials and Atoms
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ÖFOS 2012
103014 Kernphysik
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