Abstract
This work presents a direct measurement of the $^{96}$Ru($p, \gamma$)$^{97}$Rh cross section via a novel technique using a storage ring, which opens opportunities for reaction measurements on unstable nuclei. A proof-of-principle experiment was performed at the storage ring ESR at GSI in Darmstadt, where circulating $^{96}$Ru ions interacted repeatedly with a hydrogen target. The $^{96}$Ru($p, \gamma$)$^{97}$Rh cross section between 9 and 11 MeV has been determined using two independent normalization methods. As key ingredients in Hauser-Feshbach calculations, the $\gamma$-ray strength function as well as the level density model can be pinned down with the measured ($p, \gamma$) cross section. Furthermore, the proton optical potential can be optimized after the uncertainties from the $\gamma$-ray strength function and the level density have been removed. As a result, a constrained $^{96}$Ru($p, \gamma$)$^{97}$Rh reaction rate over a wide temperature range is recommended for $p$-process network calculations.
Highlights
There are 35 p nuclei on the neutron-deficient side of the valley of stability between 74Se and 196Hg, which are shielded against production by the neutron-capture processes and are produced in the p process
We present a novel method using a heavy-ion storage ring developed to measure cross sections of low-energy nuclear reactions, e.g., (p,γ ) reactions, in inverse kinematics for nuclear astrophysics
After the γ -ray strength function as well as the level density has been strongly constrained by our experimental data for 96Ru(p,γ )97Rh in the previously unexplored energy region, some additional data for this reaction between 1.6 and 3.4 MeV measured by Bork et al via the activation method [39] can help to improve the prediction of the 96Ru(p,γ )97Rh cross section further into the Gamow window, where it is sensitive to both the γ -ray strength function and the proton potential [2]
Summary
There are 35 p nuclei on the neutron-deficient side of the valley of stability between 74Se and 196Hg, which are shielded against production by the neutron-capture processes and are produced in the p process. For the 92,94Mo and 96,98Ru isotopes, an underproduction of a factor of 20–50 has been calculated for the γ process in Core Collapse Supernova models with massive stars of 13–25 M [1] This deficiency has motivated the search for additional production mechanisms, e.g., the rp process [6] or the νp process [7], and intensified efforts to remove the uncertainty in required nuclear physics parameters by measuring reaction cross sections. It was not realized until the latest achievements in producing, cooling, decelerating, and storing of heavy ions, as well as developments in the nuclear detection system at the experimental storage ring (ESR) of GSI [10] This novel technique provides a unique condition for the direct measurement of (p,γ ) reactions around the energy range of astrophysical interest [11] and has been successfully demonstrated for the first time by measuring the 96Ru(p,γ )97Rh cross section between 9 and 11 MeV/u. Experimental results of the present work allow us to constrain the most important parameters in the HF model and, provide a reliable prediction for this reaction over a wide energy range
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