Measurement of $^{34}$S($^{3}$He,p)$^{36}$Cl cross sections for early solar system nuclide enrichment

TL;DR

This study measures nuclear reaction cross sections relevant to early solar system radionuclide enrichment, providing experimental data that refine models of SLR origins and reduce uncertainties in reaction rates.

Contribution

It presents new experimental cross section measurements for the $^{34}$S($^{3}$He,p)$^{36}$Cl reaction, improving upon previous data and informing models of SLR production in the early solar system.

Findings

Cross sections increase sharply with energy, exceeding model predictions by up to 30%.

Experimental data align slightly above but are consistent with TALYS calculations.

Results help constrain nuclear reaction rates critical for understanding SLR origins.

Abstract

Isotopic studies of meteorites have provided ample evidence for the presence of short-lived radionuclides (SLRs) with half-lives of less than 100 Myr at the time of the formation of the solar system. The origins of all known SLRs is heavily debated and remains uncertain, but the plausible scenarios can be broadly separated into either local production or outside injection of stellar nucleosynthesis products. The SLR production models are limited in part by reliance on nuclear theory for modeling reactions that lack experimental measurements. Reducing uncertainty on critical reaction cross sections can both enable more precise predictions and provide constraints on physical processes and environments in the early solar system. This goal led to the start of a campaign for measuring production cross sections for the SLR $^{36}$Cl, where Bowers et al. found higher cross sections for the ${}^{33}$S($\alpha$,p)$^{36}$Cl reaction than were predicted by Hauser-Feshbach based nuclear reaction codes TALYS and NON-SMOKER. This prompted re-measurement of the reaction at five new energies within the energy range originally studied, resulting in data slightly above but in agreement with TALYS. Following this, efforts began to measure cross sections for the next most significant reaction for $^{36}$Cl production, $^{34}$S($^{3}$He,p)$^{36}$Cl. Activations were performed to produce 9 samples between 1.11 MeV/nucleon and 2.36 MeV/nucleon. These samples were subsequently measured with accelerator mass spectrometry at two labs. The resulting data suggest a sharper-than-expected rise in cross sections with energy, with peak cross sections up to 30\% higher than predictions from TALYS.