Discovery of34g,mCl(p,γ)35Arresonances activated at classical nova temperatures

Abstract

Background: The thermonuclear 34g,m Cl(p, γ) 35 Ar reaction rates are unknown due to a lack of experimental nuclear physics data. Uncertainties in these rates translate to uncertainties in 34 S production in models of classical novae on oxygen-neon white dwarfs.34 S abundances have the potential to aid in the classification of presolar grains.Purpose: Determine resonance energies for the 34g,m Cl(p, γ) 35 Ar reactions within the region of astrophyical interest for classical novae to a precision of a few keV as an essential first step toward constraining their thermonuclear reaction rates. Method:35 Ar excited states were populated by the 36 Ar(d, t) 35 Ar 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 new35 Ar levels have been detected at a statistically significant level in the region Ex ≈ 5.9-6.7 MeV (Er < 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 astrophyical interest have likely been discovered and their energies have been determined, but the resonance strengths are still unknown, and experimentally constraining the 34g,m Cl(p, γ) 35 Ar reaction rates will require further experiments.

Physics at the Munich Tandem Accelerator Laboratory

“…We have used the MLL tandem accelerator together with the Q3D magnetic spectrograph to investigate levels close to the proton emission threshold in nuclei that are formed in the reaction pathway of Novae. Nuclear states in 19 Ne [Lai13,Par15], 20 Na, 24 Al, 28 P, 32 Cl, 36 [Fry15,Fry17] have been excited with 3 He and d induced reactions. In many cases targets were used where the target element of interest was implanted into carbon foils at the Univ.…”

First spin-parity constraint of the 306 keV resonance in Cl35 for nova nucleosynthesis

“…Though studies of the mirror nucleus 35 Ar, with a half-life of under two seconds, have been undertaken (see, for example, Ref. [12]), level assignments within the region of interest based on mirror arguments are lacking, and many structure studies (see Ref. [13]) have been effectively limited to bound states by requiring high-statistics detection of γ cascades for structure information.…”

Shell-model studies of the astrophysical rp -process reactions S34(p,γ)Cl

“…In a study by Fry et al seventeen [2] new 35 Ar levels have been detected in the energy region E x = 5.9 − 6.7 MeV and their excitation energies have been determined, but not spins, parities, widths, or branching ratios. Because of the paucity of such information it is not yet pos-sible to derive meaningful experimental 34g,m Cl(p,γ) 35 Ar reaction rates.…”

“…34 S can be destroyed in novae through the 34 S(p,γ) 35 Cl reaction or bypassed by the 34 Cl(p,γ) 35 Ar reaction if the rate is fast enough to dominate the beta decay rate 34 Cl → 34 S (T 1/2 = 1.53 s for the ground state). The thermonuclear rates of these reactions are unknown at nova temperatures due to a lack of experimental nuclear physics data for the resonances up to about 800 keV above the 35 Ar proton separation energy [2]. Moreover, some nova models treat the 33 S(p,γ) 34 Cl and 34 Cl(p,γ) 35 Ar rates as total rates, without separately considering the ground state 34g Cl and the isomeric first excited state 34m Cl (Ex = 0.146 keV, T 1/2 = 2.5 min).…”