Direct Measurement of the $^{59}$Cu$(p,\alpha)^{56}$Ni Excitation Function to Constrain the Ni--Cu Cycle Strength and Its Impact on Explosive Nucleosynthesis

TL;DR

This study provides a direct measurement of a key nuclear reaction rate relevant to explosive astrophysical phenomena, refining our understanding of nucleosynthesis processes in extreme stellar environments.

Contribution

The paper presents the first direct measurement of the $^{59}$Cu$(p, extalpha)^{56}$Ni excitation function, improving constraints on the Ni--Cu cycle in astrophysical models.

Findings

Reaction rate is lower than previous evaluations.

Less than 0.1% recycling through the Ni--Cu cycle in X-ray bursts.

Enhanced efficiency of the $ u$p-process up to T_9 ≈ 3.7.

Abstract

A new direct measurement of the $^{59}$Cu$(p,\alpha){}^{56}$Ni excitation function from 2.43 to 5.88~MeV in the center-of-mass frame was performed in inverse kinematics using the high-efficiency MUSIC active-target detector at FRIB. This reaction plays a critical role in constraining the strength of the Ni--Cu cycle in explosive astrophysical environments such as Type~I X-ray bursts and the $\nu$p-process in neutrino-driven winds following core-collapse supernovae. The newly derived stellar reaction rate is systematically lower than the REACLIB evaluation, resulting in less than 0.1\% recycling through the Ni--Cu cycle in X-ray bursts and an enhanced efficiency of the $\nu$p-process up to temperatures of $T_9 \approx 3.7$.