Zn γ-Decay Probabilities for Surrogate Constraint of Neutron Capture Cross Sections*

The surrogate method is an indirect technique used to constrain cross sections of nuclear reactions inaccessible for direct measurement. This method uses an alternate reaction channel to populate a nucleus of interest, combining resulting experimental data with theory to constrain the (n,γ) cross section. Hauser-Feshbach calculations use statistical nuclear models of the desired and surrogate reactions to predict cross sections from nuclear level densities, optical model potentials, and γ-strength functions (γSF). Individual γ-decay probabilities are experimentally extracted and used to constrain γSF models and therefore the resulting n-capture cross sections. The surrogate and n-capture reaction channels each populate the excited nucleus with a different spin-parity distribution, necessitating sampling a variety of spin states to correct for this difference.

This work presents γ-decay probabilities around the relevant neutron separation energies for four Zn isotopes. Reactions measured are ^64,70Zn(p,d) and ^64,70Zn(p,t) as surrogates for ^61,62,67,68Zn(n,γ). Experimental data was collected in 2021 at Texas A&M University with a 27-MeV proton beam and Hyperion, a particle-γ coincidence array utilizing in-beam γ-ray spectroscopy. This presentation will examine notable features of the extracted γ-decays and discuss possible implications for the neutron capture cross sections.