Bulletin of the American Physical Society
52nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 66, Number 6
Monday–Friday, May 31–June 4 2021; Virtual; Time Zone: Central Daylight Time, USA
Session Q02: Towards the Thorium Nuclear ClockInvited Live
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Chair: Eric Hudson, UCLA |
Thursday, June 3, 2021 8:00AM - 8:30AM Live |
Q02.00001: Enhanced effects of violation of the fundamental symmetries, variation of the fundamental constants and dark matter field in thorium clock. Invited Speaker: Victor Flambaum Thorium clock based on 8 eV transition in 229Th nucleus has very high projected accuracy and strongly enhanced sensitivity to the effects of violation of the Lorentz invariance and Einstein equivalence principle, variation of the fundamental constants and dark matter field. Sensitivity to the variation of the fine structure constant alpha is expressed in terms of the difference between the charge radii between the excited and ground states. This gives the enhancement factor K=8000. This enhancement is also relevant to the dark matter search since interaction with dark matter leads to oscillating alpha. |
Thursday, June 3, 2021 8:30AM - 9:00AM Live |
Q02.00002: Electronic bridge processes in the 229mTh isomer Invited Speaker: Adriana Palffy Incredibly precise nuclear clocks may soon outperform and replace the present atomic clocks that define the global time standard. The only known nuclear transition in the range of vacuum-ultraviolet (VUV) lasers occurs in 229Thorium and promises such a novel and unprecedently precise nuclear clock. The nuclear excited level is a metastable state with energy of 8.19(12) eV, allowing driving with VUV lasers. As a high-precision oscillator whose frequency is predominantly determined by the strong interaction, the 229Thorium transition also offers an increased precision for the determination of fundamental constant variations. |
Thursday, June 3, 2021 9:00AM - 9:30AM Live |
Q02.00003: Measurement of the Th-229 Isomer Energy with a Magnetic Microcalorimeter Invited Speaker: Andreas Fleischmann We present a measurement of the low-energy (0–60 keV) γ-ray spectrum produced in the α-decay of U-233 using a dedicated cryogenic magnetic micro-calorimeter. The energy resolution of ∼10 eV, together with exceptional gain linearity, allows us to determine the energy of the low-lying isomeric state in Th-229 using four complementary evaluation schemes. The most precise scheme determines the Th-229 isomer energy to be 8.10(17) eV, corresponding to 153.1(32) nm, superseding in precision previous values based on γ spectroscopy, and agreeing with a recent measurement based on internal conversion electrons. We also measure branching ratios of the relevant excited states to be b29 =9.3(6)% and b42 < 0.7%. |
Thursday, June 3, 2021 9:30AM - 10:00AM Live |
Q02.00004: Demystifying the 229-Thorium Isomer: Towards the Nuclear ClockP.G. ThirolfLudwig-Maximilians-Universität München, Munich, Germany Invited Speaker: Peter G Thirolf Nowaday’s gold standard for most precise time and frequency measurements are optical atomic clocks. However, they could potentially be outperformed by a nuclear clock, which employs a nuclear transition instead of an atomic shell transition. Presently only the isomeric first excited state of 229Th qualifies to serve as a nuclear clock. For more than 4 decades nuclear physicists have targeted the identification and characterization of this elusive nuclear state (229mTh), representing the lowest nuclear excitation in the whole landscape of known isotopes. In recent years considerable progress was achieved on unveiling the properties of 229mTh: in 2016, the first direct detection of this nuclear state could be realized via its internal conversion decay branch, laying the foundation for precise studies of its decay parameters. Subsequently, a measurement of the half-life of the neutral isomer was achieved, confirming the expected reduction of 9 orders of magnitude compared to the one of charged 229mTh. Collinear laser spectroscopy was applied to resolve the hyperfine structure of the thorium isomer, providing information on nuclear moments and the nuclear charge radius. Recently, also the cornerstone on the road towards the nuclear clock, which is a precise and direct determination of the excitation energy of the isomer, could be achieved in two independent experiments, resulting in a weighted mean of the isomeric excitation energy as 8.19(12) eV. These important findings open the door towards an optical, laser-based control of 229mTh and thus the development of an ultra-precise nuclear frequency standard. Such a nuclear clock promises intriguing applications in applied as well as fundamental physics, ranging from geodesy and seismology to the investigation of possible variations of fundamental constants and the search for Dark Matter. The collaborative project ‘ThoriumNuclearClock’, funded by the European Union, recently embarked to consolidate and improve the present knowledge on the thorium isomer, realize first prototypes of a Nuclear Clock and apply them to fundamental physics studies. |
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