{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"3a4259fbea723199f47760c437b441e8490da86be403de7d9422b2797c577136","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["86b2395341c42ef83ffcb9c07000e7dbba8dfd9b5dd3dce408e7f1f1eed5f03f","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"3dbdd8444cc96ca3eb265d54c72a4844aa7de5b52aa852a6889e8a60cf38050b","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"amo.constant-variation.th229-alpha-sensitivity","kind":"well-posed","literature_status":"partially-resolved","n":"2","parents":[],"plain":"The thorium-229 nucleus has an unusually low-energy excited state that can be reached by a laser, and its frequency may react to changes in $\\alpha$ thousands of times more than atomic clocks do. How large that factor is depends on nuclear-structure numbers still poorly known.","posed_since":"2006","precise":"Define $K$ by $\\delta \\nu / \\nu = K \\delta \\alpha / \\alpha$ for the $8.36\\,\\mathrm{eV}$ Th-229 isomer transition. Combining the measured quadrupole-moment ratio ($\\Delta Q_0/Q_0 = 1.791(2)\\%$) with charge-radius data gives $K = 5900(2300)$ under a prolate-spheroid nuclear model (Beeks et al, arXiv 2407.17300, 2024). Determine $K$ with uncertainty below 10%, which requires the isomer-ground mean-square charge-radius difference to that precision and a model-independent treatment of the deformation.","problem_ref":"86b2395341c42ef83ffcb9c07000e7dbba8dfd9b5dd3dce408e7f1f1eed5f03f","references":"","settled_by":"A measurement of the isomer shift of an electronic transition in Th ions with independent atomic-theory field-shift factors, giving $\\delta(r^{2})$ between isomer and ground state to 10%.","status_note":"The 2024-2025 laser spectroscopy of Th-229 in $\\mathrm{CaF_2}$ established $K$ of order $10^{3}$ to $10^{4}$; the remaining uncertainty is about 40%.","title":"Sensitivity factor $K$ of the $\\mathrm{Th}-229$ nuclear transition to 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