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Characterization of the Near-Visible-Light Excited State of 229 Th

This research focuses on the characterization of the near-visible-light excited state of the 229Th isomer. Previous studies have used gamma-ray spectroscopy to analyze 229Th, but the 229mTh isomer has yet to be studied. Laser spectroscopy of Th2+ and measurements of hyperfine structure are used to reveal the structure and multipole moments of the isomer. This is important for its potential use as a nuclear clock. Further research aims to measure the time-dependence of coupling constants.

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Characterization of the Near-Visible-Light Excited State of 229 Th

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  1. Characterization of the Near-Visible-Light Excited State of 229Th Paul Wright

  2. 229mTh Isomer • Isomer of 229Th that exists at an excitation energy of (7.8 ± 0.5) eV • Expected to be long lived if it doesn’t quickly decay through internal conversion

  3. Previous Research • Gamma-ray spectroscopy has been used to research 229Th in the past. • 233U alpha decays into 229Ac, which undergoes beta decay. The resulting 230Th is Coulomb excited, and then a (d,t) transfer reaction results in 229Th. • Ground state of 229Th is shown to be 5/2+, second 3/2+ rotation band identified • 229mTh has yet to be analyzed by gamma-ray spectroscopy

  4. As a Nuclear Clock • Low energy can be easily excited by lasers • Less sensitive to external perturbations, and long half-life • Expected to have an uncertainty more than 10 times smaller than the current best atomic clocks

  5. Laser Spectroscopy of Th2+ Two separate radio-frequency ion traps were used, one loaded with 229,232Th2+ from laser ablation and one loaded with 229, 229mTh from recoil. Spectroscopic measurements made on both would reveal structure of the 229mTh isomer.

  6. Hyperfine Structure

  7. Multipole Moments • Measurements of the hyperfine structure allow us to determine the magnetic dipole and the electric quadrupole moments of the isomer

  8. Further Research • The more precise multipole moments measured of the isomer enable more precise uses as a nuclear clock • The high precision of the clock and the sensitivity to the coupling constant allow us to measure time-dependence of coupling constants

  9. References Thielking, J., Okhapkin, M., Glowacki, P., Meier, D., von der Wense, L., Seiferle, B., . . . Peik, E. (2018). Laser spectroscopic characterization of the nuclear-clock isomer 229mTh. Nature, 556, 321-324. Zelevinsky, V. (2011). Quantum Physics. Weinheim, Germany: Wiley-VCH. National Nuclear Data Center. (n.d.). Chart of Nuclides. Retrieved from http://www.nndc.bnl.gov

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