Exploiting Isospin Symmetry to Study the Role of Isomers in Stellar Environments

Abstract

Proton capture on the excited isomeric state of 26 Al strongly influences the abundance of 26 Mg ejected in explosive astronomical events and, as such, plays a critical role in determining the initial content of radiogenic 26 Al in presolar grains. This reaction also affects the temperature range for thermal equilibrium between the ground and isomeric levels. We present a novel technique, which exploits the isospin symmetry of the nuclear force, to address the long-standing challenge of determining proton-capture rates on excited nuclear levels. Such a technique has in-built tests that strongly support its veracity and, for the first time, we have experimentally constrained the strengths of resonances that dominate the astrophysical 26m Alðp; γÞ 27 Si reaction. These constraints demonstrate that the rate is at least a factor ∼8 lower than previously expected, indicating an increase in the stellar production of 26 Mg and a possible need to reinvestigate sensitivity studies involving the thermal equilibration of 26 Al.

Three-body optical potentials in $(d,p)$ reactions and their influence on indirect study of stellar nucleosynthesis

“…These calculations have been carried out for an incident deuteron energy of 12 MeV available at several radioactive beam facilities. We have discovered that without the I3B force the main peak cross sections σ KD03 and σ GRZ , obtained with GRZ and KD03, respectively, are very similar for populating 27 Al, 31 P * (6336) and 35 Cl excited states. Their ratio is shown in Table II.…”

“…• 34 Cl(d, p) 35 Cl as indirect probe for 34 Cl(p, γ) 35 Ar reaction that contributes to the production of 35 Ar, an important isotopic observable in pre-solar grains in meteorites. The importance of uncertainties associated with this reaction on calculations of final abundances in oxygen neon novae has previously been highlighted [13], changing abundances of 34 S sevenfold, and the ability to reduce these uncertainties is of particular importance as the 32 S/ 34 S ratio is used to determine whether grains originate from novae [15].…”

“…The importance of uncertainties associated with this reaction on calculations of final abundances in oxygen neon novae has previously been highlighted [13], changing abundances of 34 S sevenfold, and the ability to reduce these uncertainties is of particular importance as the 32 S/ 34 S ratio is used to determine whether grains originate from novae [15]. New states in 35 Cl have been identified in 36 Cl(d, t) 35 Cl reaction that include mirror analogs of astrophysical 35 Ar states [27], however, (d, t) experiment does not allow the partial proton widths Γ p to be determined.…”

“…We have performed calculations (not shown here) for two other reactions including sd-shell targets 30 P and 34 Cl at the same deuteron incident energy of 12 MeV and populating the 31 P and 35 Cl states from Table II. We came to the same conclusions about I3B effects and NN model choice as in the case of 26 Al and 56 Ni.…”

“…For very narrow proton resonances of astrophysical interest lying close to the proton threshold, where γ-decay mode dominates, it has been possible to measure the total cross sections for a population of excited final states by detecting γ-rays emitted in their de-excitation (see, for example, [11,14]). Total cross sections only were also measured in some (d, p) experiments [19,35] without the corresponding differential cross sections.…”