Total Absorption Spectroscopy of Ground and Isomeric States in ⁷⁰Cu

Theoretical models studying the origin of elements in the universe and stellar nucleosynthesis processes such the rapid neutron capture process (r-process), require physics information about beta-decay properties and neutron-capture reaction rates [1]. Currently quasiparticle random phase approximation (QRPA) calculations are used across the nuclear landscape to predict β-decay properties in astrophysical simulations [2]. QRPA calculations are typically bench-marked against known half-lives and β-delayed neutron emission probabilities, instead of comparing against the full distribution of β-decay feeding intensities (I_β) as a function of excitation energy. Nuclei with larger β-decay Q-values have decay schemes with many weak de-excitation pathways to the ground state and β-decay branches, which are difficult to measure without high efficiency detectors. Here, we use the method of total absorption spectroscopy to investigate the β-decay of ⁷⁰Cu which has three β-decaying spin-parity states (6⁻ ground state, and two isomeric states: 3⁻, and 1⁺) and is thought to be produced in the weak r-process [3, 4]. In an experiment performed at the National Superconducting Cyclotron Laboratory ⁷⁰Cu was produced, sent to the Low Energy Beam and Ion Trap (LEBIT) [5], and delivered to the Summing NaI (SuN) Total Absorption Spectrometer [6]. Spectra from the β-decay of each spin-parity state were isolated using different beam on/off periods. I_β values from total absorption spectroscopy following the β-decay of each of the three β-decaying spin-parity states will be presented and compared to Shell Model and QRPA calculations.



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