Project B04: Coherent excitation of a nucleus

Subject of the project is the study of the Th-229 nucleus with its low-energy isomer at 8.3 eV energy. This system has inspired a novel field for experiments at the interface of atomic and nuclear physics. The low energy makes the Th-229 isomer accessible to resonant laser excitation that can be studied with laser-cooled trapped ions or with thorium as a dopant in a transparent solid. The nuclear resonance can be used as the reference for an optical clock of very high accuracy. Frequency comparisons between such a nuclear clock and conventional atomic clocks based on resonances in the electron shell will provide strong sensitivity to effects of new physics beyond the standard model.

Introduction

Among all known isotopes 229Th possesses a uniquely low-lying nuclear excitation state at 7.8(5) eV (≈ 160 nm) with an unperturbed lifetime in the range of several 1000 s, possibly accessible by laser radiation. The comparatively high transition frequency and lifetime allows for building a nuclear optical clock with unprecedented relative uncertainty in the ≤10-19 range. In comparison to transitions in the electron shell, the transition frequencies of nuclear transitions are less sensitive to external perturbation fields due to the smaller size and moments of the nucleus, causing smaller shifts on the transition frequency and therefore a higher accuracy and long-term stability of such a clock.

The high uncertainty in the isomer energy and the lack of tunable laser sources in this energy range require for an alternative method of the nuclear excitation by laser radiation: An indirect excitation of the nucleus might be feasible, using the electron shell as an “antenna” to transfer energy into the nucleus via hyperfine interaction. These processes are known as electronic bridge or NEET (Nuclear Excitation by Electron Transition).

Experiments with Th+ and Th2+ ions at Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig aim at the excitation of the nucleus using these processes.

Results

During the second funding period two major instrumental developments have been concluded successfully: a setup for sympathetic laser cooling of trapped recoil ions of 229Th3+, 229mTh3+ and 230Th3+ from the α-decay of 233U and 234U, and a tunable pulsed VUV laser that provides a few GHz linewidth and high power spectral densities for the resonant excitation of 229mTh in trapped thorium ions and in Th-doped CaF2 crystals.

The first apparatus will be used for precision measurements of the hyperfine structure of 229Th3+ and 229mTh3+ in order to obtain more precise nuclear moments of these two nearly degenerate states. This will allow one to determine the difference of the Coulomb energies of both states, the parameter that determines the sensitivity of the nuclear transition frequency to the value of the fine structure constant.

The second instrument, the VUV laser source, will be used primarily for the search for nuclear excitation, first in Th-doped crystals and subsequently in trapped thorium ions. In addition, we plan to use it for a study of the electronic level structure of Th+ in the energy range of the nuclear isomer, in order to gain more understanding on the relevance of electronic bridge processes for the nuclear decay of the isomer in this charge state.


Publications

Showing results 1 - 7 out of 7

Tiedau J, Okhapkin MV, Zhang K, Thielking J, Zitzer G, Peik E et al. Laser Excitation of the Th-229 Nucleus. Physical review letters. 2024 Apr 29;132(18):182501. doi: 10.1103/PhysRevLett.132.182501
Thielking J, Zhang K, Tiedau J, Zander J, Zitzer G, Okhapkin MV et al. Vacuum-ultraviolet laser source for spectroscopy of trapped thorium ions. New journal of physics. 2023 Aug 14;25(8):083026. 083026. doi: 10.1088/1367-2630/aced1b
Głowacki P, Peik E. Fluorescence properties of ions adsorbed from aqueous solutions on fused silica and CaF2 - Test cases of Eu3+ and Tb3+. Journal of luminescence. 2022 Jul 1;247:118865. 118865. doi: 10.1016/j.jlumin.2022.118865
Meier DM, Thielking J, Głowacki P, Okhapkin MV, Müller RA, Surzhykov A et al. Electronic level structure of Th+ in the range of the Th 229m isomer energy. Physical Review A. 2019 May 29;99(5):052514. doi: 10.1103/PhysRevA.99.052514
Müller RA, Maiorova AV, Fritzsche S, Volotka AV, Beerwerth R, Glowacki P et al. Hyperfine interaction with the Th 229 nucleus and its low-lying isomeric state. Physical Review A. 2018 Aug 20;98(2):020503. doi: 10.1103/PhysRevA.98.020503
Safronova MS, Porsev SG, Kozlov MG, Thielking J, Okhapkin MV, Głowacki P et al. Nuclear Charge Radii of Th 229 from Isotope and Isomer Shifts. Physical review letters. 2018 Nov 21;121(21):213001. doi: 10.1103/PhysRevLett.121.213001
Thielking J, Okhapkin MV, Głowacki P, Meier DM, Von Der Wense L, Seiferle B et al. Laser spectroscopic characterization of the nuclear-clock isomer 229mTh. NATURE. 2018 Apr 19;556(7701):321-325. doi: 10.1038/s41586-018-0011-8
All publications of the Collaborative Research Centre

Project leader

PD Dr. Ekkehard Peik
Address
Bundesallee 100
38116 Braunschweig
PD Dr. Ekkehard Peik
Address
Bundesallee 100
38116 Braunschweig

Staff

Dr. Maksim Okhapkin
Address
Physikalisch-Technische Bundesanstalt
Bundesallee 100
38116 Braunschweig
Dr. Maksim Okhapkin
Address
Physikalisch-Technische Bundesanstalt
Bundesallee 100
38116 Braunschweig
David-Marcel Meier, M.Sc.
Address
Physikalisch-Technische Bundesanstalt
Bundesallee 100
38116 Braunschweig
David-Marcel Meier, M.Sc.
Address
Physikalisch-Technische Bundesanstalt
Bundesallee 100
38116 Braunschweig
Johannes Thielking, M.Sc.
Address
Physikalisch-Technische Bundesanstalt
Bundesallee 100
38116 Braunschweig
Johannes Thielking, M.Sc.
Address
Physikalisch-Technische Bundesanstalt
Bundesallee 100
38116 Braunschweig
Gregor-Alexander Zitzer, M.Sc.
Address
Physikalisch-Technische Bundesanstalt
Bundesallee 100
38116 Braunschweig
Gregor-Alexander Zitzer, M.Sc.
Address
Physikalisch-Technische Bundesanstalt
Bundesallee 100
38116 Braunschweig