X-ray pumping of the nuclear-clock isomer 229-Th

by Prof. Noboru Sasao (Okayama University)

Wednesday 12 Jun 2019, 10:30 → 11:30 Asia/Shanghai

B105 (CHEP)

Thorium-229 is a unique case in nuclear physics: it presents a metastable first excited state 229mTh, just a few electronvolts above the nuclear ground state. This so-called isomer is accessible by VUV lasers, which allows transferring the amazing precision of atomic laser spectroscopy to nuclear physics. Being able to manipulate the 229Th nuclear states at will opens up a multitude of prospects, from studies of the fundamental interactions in physics to applications as a compact and robust nuclear clock. However, direct optical excitation of the isomer or its radiative decay back to the ground state has not yet been observed, and a series of key nuclear structure parameters such as the exact energies and half-lives of the low-lying nuclear levels of 229Th are yet unknown. Here we present the first active optical pumping into 229mTh. Our scheme employs narrow-band 29 keV synchrotron radiation to resonantly excite the second excited state, which then predominantly decays into the isomer. We determine the resonance energy, measure a half-life and an excitation linewidth, and extract the branching ratio of the second excited state into the ground and isomeric state respectively. These measurements allow us to re-evaluate gamma spectroscopy data that have been collected over 40 years. In the talk, I will explain the experiment in more detail as well as possible applications. See the reference below for more detail. arXiv:1902.04823 Personal Introduction: The speaker, Noboru Sasao, is a professor of the Research Institute for Interdisciplinary Science, Okayama University, Japan. He received a Ph.D degree from Yale University in 1976 on “Deep Inelastic Scattering of Polarized Electrons by Polarized Protons”. Since 1978, in which he obtained a position at Kyoto University, Japan, he had been mainly involved in accelerator-based high-energy particle physic experiments. Those include rare kaon decay experiments at KEK, a parity violation experiment at SLAC, TRISTAN electron-positron collider experiments, an axion search experiment at KEK, etc. He moved to Okayama University in 2009 to promote an interdisciplinary project which combines atomic physics with fundamental physics. His main interests at present are “neutrino mass spectroscopy with atoms”, “dark-matter axion search experiment using quantum coherence amplification principle”, and “determination of Thorium 229 isomer energy towards realization of nuclear clocks”.