The 229Th Isomer Line as a Reference for a High-Precision Frequency Standard
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The use of the nuclide 229Th as a new nuclear-optical frequency standard is studied theoretically. The mechanism for two-photon optical pumping of the 7.6 eV isomer through the optical shell in singly charged ions is examined. The decisive role of the 8s–7s resonance transition is demonstrated. It is shown that the required energy of the two photons is equal to the sum of the energies of the nuclear level and the 7s-state of the atom. The lifetime of the isomer in the singly charged ion is 165 sec.
Keywordsoptical frequency standard nuclear frequency standard 229mTh isomer nuclear clock nuclear excitation by electronic transition
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