Determining the ⁹⁵Zr(n, γ) and ⁹³Zr(n, γ) cross sections via ⁹⁶Zr(p, p’) and ⁹⁴Zr(p, p’) surrogate reactions

The surrogate-reaction method can improve our understanding of s-process nucleosynthesis. Branch-point nuclei are a crucial feature of the s-process that highly impact the elemental abundances. Knowing the (n, γ) cross sections of these nuclei allows for powerful constraints to be placed on the stellar conditions of the parent stars in which the elements originated. However, a large number of branch-point nuclei have half-lives on the order of months or less, making the use of direct-measurement techniques challenging, if not impossible. An experiment was performed in which the surrogate-reaction method was used to obtain the (n, γ) cross section for ⁹⁵Zr (64-day half-life), whose branching has been observed in presolar stardust grains. Inelastic proton scattering from the stable isotope ⁹⁶Zr served as the surrogate. The measurement was carried out at the Texas A&M University K150 Cyclotron. An enriched ⁹⁶Zr foil was bombarded with 20-MeV protons. Scattered protons and coincident γ rays were measured with the LLNL Hyperion array, which consists of three segmented annular silicon detectors in a dE-E1-E2 configuration surrounded by an array of BGO Compton-suppressed HPGe Clover detectors. A benchmark was also performed using ⁹⁴Zr(p, p’) to determine the ⁹³Zr(n, γ) cross section, which has been previously measured via direct methods. Details of the experiment and preliminary results will be discussed.