Title: Experimental study of ${}^{35}\mathrm{Cl}$ excited states via ${}^{32}\mathrm{S}(\alpha ,p)$

Abstract

The presolar grains originating in oxygen-neon novae may be identified more easily than those of other stellar sources if their sulfur isotopic ratios ($$^{33}\mathrm{S}/^{32}\mathrm{S}$$ and $$^{34}\mathrm{S}/^{32}\mathrm{S}$$) are compared with the theoretical ones. The accuracy of such a comparison depends on reliable $$^{33}\mathrm{S}(p,{\gamma})^{34}\mathrm{Cl}$$ and $$^{34}\mathrm{S}(p,{\gamma})^{35}\mathrm{Cl}$$ reaction rates at the nova temperature regime. The latter rate has recently been computed based on experimental input, and many new excited states in $$^{35}\mathrm{Cl}$$ were discovered above the proton threshold. As a result, the experimental $$^{34}\mathrm{S}(p,{\gamma})^{35}\mathrm{Cl}$$ rate was found to be less uncertain and 2–5 times smaller than the theoretical one. Consequently, the simulated $$^{34}\mathrm{S}/^{32}\mathrm{S}$$ isotopic ratio for nova presolar grains was predicted to be smaller than that of type II supernova grains by a factor of 1.5 to 3.7. The present study was performed to confirm the existence of these new resonances, and to improve the remaining uncertainties in the ${}_{34}\mathrm{S}(p,\gamma ){}_{35}\mathrm{Cl}$ reaction rate. Energies and spin-parities of the ${}_{35}\mathrm{Cl}$ excited levels were investigated via high-resolution charged-particle spectroscopy with an Enge split-pole spectrograph using the ${}_{32}\mathrm{S}(\alpha ,p){}_{35}\mathrm{Cl}$ reaction. Differential cross sections of the outgoing protons were measured at $E_{\alpha }=21$ MeV. Distorted-wave Born approximation calculations were carried out to constrain the spin-parity assignments of observed levels, with special attention to those significant in determination of the ${}_{34}\mathrm{S}(p,\gamma ){}_{35}\mathrm{Cl}$ reaction rate over the nova temperature regime. The existence of these newly discovered states are largely confirmed, although a few states were not observed in this study. The spins and parities of a few ${}_{35}\mathrm{Cl}$ states were assigned tentatively for the first time. The present ${}_{34}\mathrm{S}(p,\gamma ){}_{35}\mathrm{Cl}$ experimental thermonuclear reaction rate at 0.1–0.4 GK is consistent within $1\sigma$ with the previous evaluation. However, our rate uncertainty is larger than before due to a more realistic treatment of the uncertainties in the rate input. In comparison with the previous rate evaluation, where the high and low rates differed by less than a factor of 2 over the nova temperature regime, the ratio of the present limit rates is at most a factor of 3.5 at 0.12 GK. At temperatures above 0.2 GK, we recommend the future work to focus on determination of the unknown properties of four excited states of ${}_{35}\mathrm{Cl}$: 6643, 6761, 6780, and 6800 keV.

Authors:

Setoodehnia, K. ^[1]; Kelley, J. H. ^[1]; Marshall, C. ^[1]; Portillo Chaves, F. ^[1]; Longland, R. ^[1]

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+ Show Author Affiliations

1. North Carolina State Univ., Raleigh, NC (United States). Dept. of Physics; Duke Univ., Durham, NC (United States). Triangle Universities Nuclear Lab.

Publication Date:

Thu May 30 00:00:00 EDT 2019

Research Org.:

North Carolina State University, Raleigh, NC (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Nuclear Physics (NP)

OSTI Identifier:

1523613

Alternate Identifier(s):

OSTI ID: 1523554

Grant/Contract Number:  

SC0017799; FG02-97ER41041

Resource Type:

Accepted Manuscript

Journal Name:

Physical Review C

Additional Journal Information:

Journal Volume: 99; Journal Issue: 5; Journal ID: ISSN 2469-9985

Publisher:

American Physical Society (APS)

Country of Publication:

United States

Language:

English

Subject:

73 NUCLEAR PHYSICS AND RADIATION PHYSICS; explosive burning; H & He induced nuclear reactions; nuclear astrophysics; transfer reactions