Speaker
Description
Sensitivity studies have identified the $^{59}$Cu(p, $\gamma$)$^{60}$Zn and $^{59}$Cu(p, $\alpha$)$^{56}$Ni reaction rates as quantities which strongly affect the light curve and ash composition of type I X-ray bursts, and the production of $^{59}$Ni by the $\nu p$ process in supernovae. The relative rates of these reactions will determine the strength of the NiCu cycle: $^{59}$Cu(p, $\alpha$) inhibits production of heavier elements while $^{59}$Cu(p, $\gamma$) allows nucleosynthesis to continue onto heavier elements. Prior experiments have directly measured the $^{59}$Cu(p,$\alpha$) reaction rate above the Gamow window for X-ray bursts, and single nucleon transfer reactions were used to discover resonances and obtain proton spectroscopic factors for resonances within the Gamow window for X-ray bursts.
In November of 2025, FRIB Experiment E23035 used the GADGET II system, which consists of a time projection chamber surrounded by the DEGAi germanium array, to discover resonances in $^{60}$Zn, and measure the associated proton, $\alpha$-particle, and $\gamma$-ray branching ratios. A $^{60}$Ga beam was implanted in the time projection chamber and the $\beta$ decay of $^{60}$Ga populated excited states in $^{60}$Zn, including states within the Gamow windows for both X-ray bursts and the $\nu$p process. The time projection chamber was used to identify and measure the energy of $\beta$-delayed protons and $\alpha$-particles, and the germanium array detected gamma rays. These measurements provide information about the relative rates of $^{59}$Cu(p, $\gamma$) and $^{59}$Cu(p, $\alpha$) reactions, for the first time providing experimental information about competition between the (p,$\alpha$) and (p, $\gamma$) reactions at the energies relevant to the rp and $\nu$p processes. Absolute reaction rates will be calculated by identifying measured resonances with shell model states and using the shell model lifetimes of those states to calculate resonance strengths. Preliminary results including newly discovered resonances and corresponding branching ratios will be presented.
This work has been supported by the U. S. Department of Energy under award no: DE-SC0016052 and DE-SC0024587, and the U. S. National Science Foundation under award no: 1565546, 1913554, 2209429, and 2514797.
| Career stage | Graduate student |
|---|