Discovery of Cl-34g,Cl-m(p,gamma)Ar-35 resonances activated at classical nova temperatures

Abstract

Background: The thermonuclear Cl-34g,Cl-m(p,gamma)Ar-35 reaction rates are unknown due to a lack of experimental nuclear physics data. Uncertainties in these rates translate to uncertainties in S-34 production in models of classical novae on oxygen-neon white dwarfs. S-34 abundances have the potential to aid in the classification of presolar grains.; Purpose: Determine resonance energies for the Cl-34g,Cl-m(p,gamma)Ar-35 reactions within the region of astrophysical interest for classical novae to a precision of a few keV as an essential first step toward constraining their thermonuclear reaction rates.; Method: Ar-35 excited states were populated by the Ar-36(d,t)Ar-35 reaction at E(d) = 22 MeV and reaction products were momentum analyzed by a high resolution quadrupole-dipole-dipole-dipole (Q3D) magnetic spectrograph.; Results: Seventeen new Ar-35 levels have been detected at a statistically significant level in the region E-x approximate to 5.9-6.7 MeV (E-r < 800 keV) and their excitation energies have been determined to typical uncertainties of 3 keV. The uncertainties for five previously known levels have also been reduced substantially. The measured level density was compared to those calculated using the WBMB Hamiltonian within the sd-pf model space.; Conclusions: Most of the resonances in the region of astrophysical interest have likely been discovered and their energies have been determined, but the resonance strengths are still unknown, and experimentally constraining the Cl-34g,Cl-m(p,gamma)Ar-35 reaction rates will require further experiments.