Detailed Study of the $^{59}$Cu(p,$\alpha)^{56}$Ni Reaction and Constraints on Its Astrophysical Reaction Rate

TL;DR

This study provides a direct measurement of the $^{59}$Cu(p,$ extalpha$)$^{56}$Ni reaction rate, crucial for understanding nucleosynthesis in explosive astrophysical environments, and constrains its rate to improve astrophysical models.

Contribution

First direct measurement of the $^{59}$Cu(p,$ extalpha$)$^{56}$Ni reaction excitation function using inverse kinematics at FRIB, refining the astrophysical reaction rate.

Findings

The stellar reaction rate is systematically lower than the REACLIB rate.

The rate remains below the $(p, extgamma)$ rate for temperatures $T_9 extless 3$.

Provides tighter constraints on nucleosynthesis models in X-ray bursts.

Abstract

The $^{59}$Cu$(p,\alpha)^{56}$Ni reaction plays an important role in explosive astrophysical scenarios such as Type I X-ray bursts and the $\nu p$-process in neutrino-driven winds following a core-collapse supernova. In both cases, this reaction has been proposed to significantly affect the synthesis of heavier nuclei by regulating the flow of nucleosynthesis through the Ni--Cu cycle. In this work, we present a direct measurement of the $^{59}\mathrm{Cu}(p,\alpha)^{56}\mathrm{Ni}$ excitation function from 2.43--5.88 MeV in the center-of-mass frame. The experiment was performed in inverse kinematics using the high-efficiency MUSIC active-target detector at FRIB. This measurement allowed tight constraints to be placed on the astrophysical reaction rate. The derived stellar rate is systematically lower than the REACLIB rate and remains below the competing $(p,\gamma)$ rate for $T_9 \lesssim 3$.