{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"805441b66b6c71f55775ce14062f1c228f0d5e9ab8064d143802509967ec41e6","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["82ebf3a9c8b680f6b8db3662f3b8d616b125ad060d1b9b4452831fdf538d531b","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"c08f94ee8ddb8e55dfca2805887ce410d8b62bcf22352a697a24cc2372a30b16","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"nuc.stellar-reaction-rates.c12-alpha-gamma","kind":"well-posed","literature_status":"open","n":"2","parents":[],"plain":"When helium burns in a star, carbon-12 captures a helium nucleus to become oxygen-16 at a rate nobody has measured at the relevant energy. This one rate fixes the carbon-to-oxygen ratio of stars and the masses of the black holes they leave.","posed_since":"","precise":"Determine the total astrophysical S-factor $S_{\\mathrm{tot}}(E_{\\mathrm{cm}}=300\\,\\mathrm{keV})$ of $\\mathrm{12C}(\\alpha,\\gamma)\\mathrm{16O}$ (E1 and E2 ground-state transitions plus cascades), at the Gamow peak for $T \\sim 2 \\times 10^{8}\\,\\mathrm{K}$, with total uncertainty below 10 percent. Direct data stop near $E_{\\mathrm{cm}} \\sim 1\\,\\mathrm{MeV}$, so the answer requires either direct data closer to 300 keV or an R-matrix extrapolation whose subthreshold-state inputs (1- at 7.12 MeV and 2+ at 6.92 MeV in 16O) are fixed to the needed accuracy.","problem_ref":"82ebf3a9c8b680f6b8db3662f3b8d616b125ad060d1b9b4452831fdf538d531b","references":"","settled_by":"A direct measurement below $E_{\\mathrm{cm}} \\sim 0.8\\ \\mathrm{MeV}$ at an underground or high-intensity facility combined with a global $R$-matrix fit that reduces $S_{\\mathrm{tot}}(300\\ \\mathrm{keV})$ to under 10 percent uncertainty.","status_note":"The 2017 R-matrix evaluation (deBoer et al.) remains the reference; no direct measurement has yet reached the Gamow window.","title":"The $12\\mathrm{C}(\\alpha,\\gamma)16\\mathrm{O}$ rate at helium-burning energies to 10 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