LMU München

The LMU team forms part of the nuclear physics group working at the LMU Chair of Medical Physics in Garching, operating its experimental facilities at the Maier-Leibnitz Laboratory.

We focus on a direct identification of the 229mTh ground-state transition and an improved determination of its transition wavelength as a prerequisite for the development of a suitable laser system able to directly control the laser excitation of the Th isomer. The experimental concept is based on a spatial decoupling between the population of the 229mTh isomer (via a decay from 233U) and the detection of its ground-state decay. This is achieved by using a buffer-gas stopping cell, where the 233U source is mounted, and a recoil nuclei are thermalized, extracted, phase-space-cooled and mass separated from accompanying a decay chain daughter products of 233U (and a minor 232U contamination of about <10-6 in the source).

Subsequently, two routes are pursued to search for the ground state decay. The first one directly targets the UV fluorescence. Here the extracted and separated isomeric nuclei are

being focused and collected on a micro electrode. Thus any prompt background is left in the gas cell and in the subsequent UV optical system the isomeric decay can be studied in a clean environment. To this end the collection electrode is placed in the focus of an annular parabolic mirror that collects and parallelizes the fluorescence light from the ground-state transition, sending it to a second annular deep parabolic mirror, whose distant focal point lies behind the mirror, in the plane of a multi-channel-plate detector (whose photo-electrons are accelerated towards a phosphorus screen, where they are registered by a sensitive CCD camera).

The second approach aims at detecting electrons from the isomeric decay via internal conversion (IC), using the same MCP/CCD combination for position-sensitive electron detection.

Provided a positive outcome of our isomeric transition search, the next step to be addressed would be the preparation of the 229mTh ions, preferably in the 3+ charge state, for half-life determination and ultimately laser manipulation in a cryogenic linear Paul trap to be set up within the framework of nuClock.

LMU München
group webpage


Publications of the LMU group

Laser spectroscopic characterization of the nuclear clock isomer 229mTh

Johannes Thielking, Maxim V. Okhapkin, Przemyslaw Glowacki, David M. Meier, Lars von der Wense, Benedict Seiferle, Christoph E. Düllmann, Peter G. Thirolf, and Ekkehard Peik

A Laser Excitation Scheme for 229mTh

Lars von der Wense, Benedict Seiferle, Simon Stellmer, Johannes Weitenberg, Georgy Kazakov, Adriana Pálffy, and Peter G. Thirolf
arXiv:1709.05524 and Phys. Rev. Lett. 119, 132503 (2017)

Feasibility Study of Internal Conversion Electron Spectroscopy of Th-229m

Benedict Seiferle, Lars von der Wense, and Peter G. Thirolf
arXiv:1702.00398 and Eur. Phys. Jour. A 53, 108 (2017)

Lifetime Measurement of the Th-229 Nuclear Isomer

Benedict Seiferle, Lars von der Wense, and Peter G. Thirolf
Phys. Rev. Lett. 118, 042501 (2017)

Direct detection of the Th-229 nuclear clock transition

Lars von der Wense, Benedict Seiferle, Mustapha Laatiaoui, Jürgen B. Neumayr, Hans-Jörg Maier, Hans-Friedrich Wirth, Christoph Mokry, Jörg Runke, Klaus Eberhardt, Christoph E. Düllmann, Norbert G. Trautmann, and Peter G. Thirolf
arXiv:1710.11398 and Nature 533, 47 (2016)

The extraction of 229Th3+ from a buffer-gas stopping cell

L. v. d. Wense, B. Seiferle, M. Laatiaoui, and P. G. Thirolf
online publication (2016)

A VUV detection system for the direct photonic identification of the first excited isomeric state of Th-229

Benedict Seiferle, Lars von der Wense, Mustapha Laatiaoui, and Peter G. Thirolf
Eur. Phys. Jour. A 70, 58 (2016)

Determination of the extraction efficiency for U-233 source recoil ions from the MLL buffer-gas stopping cell

L. v. d. Wense, B. Seiferle, M. Laatiaoui, and P. G. Thirolf
Eur. Phys. Jour. A 51, 29 (2015)

Towards an all-optical access to the lowest nuclear excitation in Th-229m

P. G. Thirolf, L. v. d. Wense, D. Kalb, and M. Laatiaoui
Acta Phys. Pol. B 44, 391 (2013)

Towards a direct transition energy measurement of the lowest nuclear excitation in Th-229

L. v. d. Wense, P. G. Thirolf, D. Kalb, and M. Laatiaoui
arXiv:1211.0710 and JINST 8, P03005 (2013)

Contact persons

Peter Thirolf

Lars von der Wense


Benedict Seiferle