Can COSI detect $γ$-ray lines from rare isotopes produced in the astrophysical intermediate neutron-capture process?

[2605.27829] Can COSI detect $γ$-ray lines from rare isotopes produced in the astrophysical intermediate neutron-capture process? Skip to main content Search Submit Donate Log in Search arXiv Press Enter to search · Advanced search Astrophysics > High Energy Astrophysical Phenomena arXiv:2605.27829 (astro-ph) [Submitted on 27 May 2026 ( v1 ), last revised 14 Aug 2026 (this version, v3)] Title: Can COSI detect $γ$-ray lines from rare isotopes produced in the astrophysical intermediate neutron-capture process? Authors: Falk Herwig , Pavel Denissenkov , Eric Burns View a PDF of the paper titled Can COSI detect $\gamma$-ray lines from rare isotopes produced in the astrophysical intermediate neutron-capture process?, by Falk Herwig and 2 other authors View PDF HTML (experimental) Abstract: We investigate the nuclear $\gamma$-ray line emission from rare isotopes produced in the astrophysical intermediate neutron-capture process ($i$ process) and assess the prospects of observing these emissions with $\gamma$-ray telescopes. The astrophysical sites of the $i$ process remain uncertain, but two candidates with predicted rapid mass ejections at metallicities of stars in the solar neighborhood are post-asymptotic giant branch (post-AGB) stars, such as Sakurai's object (V4334 Sagittarii), and rapidly-accreting white dwarfs (RAWDs). Detailed 1D and 3D simulations indicate that the convective-reactive fluid dynamics responsible for $i$-process nucleosynthesis can lead to violent, non-radial outbursts resulting in mass ejections of $i$-process products. We calculate ejected yields of rare isotopes whose radioactive decays may produce detectable $\gamma$-ray lines, particularly in the 0.5-2 MeV range, focusing on $^{22}$Na, $^{89}$Sr, and $^{95}$Zr. We estimate the formation rates of these sources and the likelihood of detecting their $\gamma$-ray emissions within 1000 parsecs of the Sun. The probability of observing $i$-process emission lines during COSI's operational period is up to $\approx 1\%$, rising to $11\%$ for $^{89}$Sr if observed within a few days. Due to the long lifetime and large production of $^{22}$Na from proton-capture reactions its detection is more likely, with a probability of $\approx 5\%$. Future space missions could increase the observation probability to several tens of percent. Detection of long-lived neutron-rich isotopes such as $^{137}$Cs would provide the first direct $\gamma$-ray signature of intermediate neutron-density nucleosynthesis, distinguishing the $i$ process from classical s- and r-process pathways. (abridged) Comments: Phys. Rev. Lett., accepted. references updated Subjects: High Energy Astrophysical Phenomena (astro-ph.HE) ; Solar and Stellar Astrophysics (astro-ph.SR) Cite as: arXiv:2605.27829 [astro-ph.HE] (or arXiv:2605.27829v3 [astro-ph.HE] for this version) https://doi.org/10.48550/arXiv.2605.27829 Focus to learn more arXiv-issued DOI via DataCite Related DOI : https://doi.org/10.1103/4qlh-47vb Focus to learn more DOI(s) linking to related resources Submission history From: Falk Herwig [ view email ] [v1] Wed, 27 May 2026 01:34:10 UTC (142 KB) [v2] Fri, 12 Jun 2026 23:26:31 UTC (143 KB) [v3] Fri, 14 Aug 2026 21:29:20 UTC (144 KB) Full-text links: Access Paper: View a PDF of the paper titled Can COSI detect $\gamma$-ray lines from rare isotopes produced in the astrophysical intermediate neutron-capture process?, by Falk Herwig and 2 other authors View PDF HTML (experimental) TeX Source view license Additional Features Audio Summary Current browse context: astro-ph.HE < prev | next > new | recent | 2026-05 Change to browse by: astro-ph astro-ph.SR References & Citations INSPIRE HEP NASA ADS Google Scholar Semantic Scholar 1 blog link ( what is this? ) export BibTeX citation Loading... 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