News

Lars von der Wense wins DPG thesis prize

Every year, the German Physics Society (DPG) offers a PhD thesis prize for each of its sections. This year, Lars von der Wense of LMU Munich was awarded the thesis prize in the section “Matter and Cosmos”. Congratulations to Lars, his supervisor Peter G. Thirolf, and the whole team at LMU for this prestigious recognition!

EFTF in Torino: EFTF Award 2018 goes to Ekkehard Peik

This year’s European Frequency and Time Forum (EFTF) is already the 32nd edition of this conference series and will take place in Torino, Italy, during the upcoming week. This conference is one of the global gathering of researchers involved with the measurement and distribution of time and frequencies; the conference webpage can be found here. Each year, a European Time and Frequency Award is given to an outstanding researcher to recognize his or her work. This year’s EFTF Laureate is Ekkehard Peik (PTB), one of the driving forces behind the nuClock project. He will receive the award “for seminal contributions to single-ion optical frequency standards and high-precision spectroscopy thereby establishing most stringent limits on possible variations of fundamental constants”. Congratulations to Ekkehard for being this year’s EFTF Laureate!

New experimental values for the Th-229m isomer energy and lifetime

The Th-229 nuclear isomer has been around for more than 40 years already, but two of its main properties, namely its energy and lifetime, are known only with very large error margins. While there is no experimental value for the bare isomer lifetime at all, there is at least some consensus on the isomer energy (somewhere between 6.3 and 10 eV). In their recent study (now available on the arXiv preprint server here), the Russian group at MEPhI suggests an energy of 7.1 eV and a lifetime of about half an hour for the bare isomer. These values are in agreement with all recent experiments, which is very good news. And it’s the first time since the Beck et al. measurement (more than 10 years ago !) that a research team dares to put forward a value of the isomer energy. Let’s hope that an independent experiment using a different approach will soon be able to confirm this value. Congratulations to the Russian team for their work!

New publication on the joint TU Wien & PTB work to directly excite the isomer

The TU Wien group and the Metrology Light Source (MLS) in Berlin (a part of PTB) have joined forces to directly excite the Thorium isomer in the VUV. In a measurement campaign about a year ago, Th-229 doped crystals were illuminated by tunable undulator radiation at the MLS facility. A wavelength region between 124 and 240 nm was probed (5.2 to 10 eV) at illumination & detection times between 30 and 600 seconds. The result of this study has now been made available on the arXiv preprint server (find the publication here).

In short, massive photoluminescence masked any possible gamma emission of the isomer. Three different types of photocathodes were used (Cs-Te, Cs-I, diamond), where only the Cs-I version was capable of supressing the photoluminescence at longer wavelengths to a degree that allowed researchers to draw any conclusions on the energy and lifetime of the isomer. Assuming radiative decay as the only decay channel, an isomer lifetime between 0.2 and 1.1 seconds can be excluded for an isomer energy between 7.5 and 10 eV (the region of highest sensitivity of the Cs-I detector). This study complements earlier work in the group of Eric Hudson at UCLA, where a parameter region of similar energy, but longer lifetime was excluded. Also, the results of this study are in agreement with the work at LMU.

Although not successful in this campaign, the results give direct input to the design and protocol of the next round of measurements.

A new review paper on nuclear clocks

Researchers at LMU Munich have put together a new review paper on the history of work on the Th-229 isomer, its current status, as well as potential implementations of a nuclear clock. The paper also investigates the properties of other candidates (aside from Th-229) to be used for a nuclear clock. It was assembled in connection with a talk given by Lars von der Wense at last year’s 175th anniversary of the Mendeleev All-Russia Research Institute of Metrology (VNIIM) in St. Petersburg, and can be downloaded here.