Determination of the ${}^{60}$Zn level density from neutron evaporation spectra

Abstract

Nuclear reactions of interest for astrophysics and applications often rely on statistical model calculations for nuclear reaction rates, particularly for nuclei far from $\beta$-stability. However, statistical model parameters are often poorly constrained, where experimental constraints are particularly sparse for exotic nuclides. For example, our understanding of the breakout from the NiCu cycle in the astrophysical rp-process is currently limited by uncertainties in the statistical properties of the proton-rich nucleus ${}^{60}$Zn. We have determined the nuclear level density of ${}^{60}$Zn using neutron evaporation spectra from ${}^{58}$Ni(${}^3$He, n) measured at the Edwards Accelerator Laboratory. We compare our results to a number of theoretical predictions, including phenomenological, microscopic, and shell model based approaches. Notably, we find the ${}^{60}$Zn level density is somewhat lower than expected for excitation energies populated in the ${}^{59}$Cu(p,$\gamma$)${}^{60}$Zn reaction under rp-process conditions. This includes a level density plateau from roughly 5-6 MeV excitation energy, which is counter to the usual expectation of exponential growth and all theoretical predictions that we explore. A determination of the spin-distribution at the relevant excitation energies in ${}^{60}$Zn is needed to confirm that the Hauser-Feshbach formalism is appropriate for the ${}^{59}$Cu(p,$\gamma$)${}^{60}$Zn reaction rate at X-ray burst temperatures.

arXiv comment10 pages, 8 figures

References in corpus (14)

• Extraction of level density and gamma strength function from primary gamma spectra
• Dependence of X-Ray Burst Models on Nuclear Reaction Rates
• Novel technique for constraining r-process (n,$\gamma$) reaction rates
• Relevant energy ranges for astrophysical reaction rates
• Sensitivity of astrophysical reaction rates to nuclear uncertainties
• Nuclear Physics of the Outer Layers of Accreting Neutron Stars
• Influence of Nuclear Reaction Rate Uncertainties on Neutron Star Properties Extracted From X-ray Burst Model-Observation Comparisons
• Fine structure of the isovector giant dipole resonance in 208Pb: Characteristic scales and level densities
• Experimental level densities of atomic nuclei
• Test of nuclear level density inputs for Hauser-Feshbach model calculations
• The Edwards Accelerator Laboratory at Ohio University
• Microscopic calculations of nuclear level densities with the Lanczos method
• Applicability Of The Hauser-Feshbach Approach For The Determination of Astrophysical Reaction Rates
• Pairing properties from random distributions of single-particle energy levels

Cited by in corpus (3)

• Horizons: Nuclear Astrophysics in the 2020s and Beyond
• First direct measurement of ${}^{59}$Cu(p,$\alpha$)${}^{56}$Ni: A step towards constraining the Ni-Cu cycle in the Cosmos
• Extension of the particle x-ray coincidence technique: The lifetimes and branching ratios apparatus