{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"f117ae5900814ad2655b043fcae714f3729d14c37578256d8a6ab37b8def4c4f","created":"2026-10-03T07:17:53Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"fac0bcdb53b0e9c6c5f33fe69ac98bf4b666d08f493094cd8a0ab65b24f76996","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":"1","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":null,"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 CaF2 established $K$ of order 1e3 to 1e4; the remaining uncertainty is about 40%.","title":"Sensitivity factor $K$ of the $\\mathrm{Th}-229$ nuclear transition to $\\alpha$","topic_ref":"0d5d25a5bcd4a09341050ed67516a89341dcb76395d21eb07382fa82d8edaaf2"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"86b2395341c42ef83ffcb9c07000e7dbba8dfd9b5dd3dce408e7f1f1eed5f03f","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"eac74472b4da2093ce1eead1c4964eb855bb32d85cc50ce4c04f2148c3a368f0","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"1QBWgxUiTGxDRJkV_0Fl7R76ZJSjIGPCyJopML_qLz9vtjbiM0Y3C1zXOGnXHXbjPZF-AHQ7BZWZNkXHYTeGAA"},"schema":"pubphys.envelope/1"},"record_hash":"86b2395341c42ef83ffcb9c07000e7dbba8dfd9b5dd3dce408e7f1f1eed5f03f","leaf_index":394}