The nuClock team will organize an international conference on all topics related to the Thorium-229 isomer. Today, we are proud to announce the date and venue! The conference will take place on July 9 to 12, 2018 in the unique old physics center in Bad Honnef, Germany.

The location: The small town of Bad Honnef is beautifully located at the Rhine river, about 45 km south of Cologne. It can nicely be reached by train from the airport of Cologne, as well as from Frankfurt airport. The physics center has quite a remarkable history that goes back about 120 years; more information can be found here. Today, it features three state-of-the-art lecture halls and accomodation of about 80 people.

The conference: The main topic of the conference is the work towards a nuclear clock based on Th-229, and we seek to gather all groups around the world that work towards this goal. Further topics include other novel types of optical clocks (e.g. highly charged ions) and applications in geodesy.

The registration: Registration will open later this year, we will send around newsletters and post all information on the nuClock website. Seating capacity limits the number of participants to about 80.

More information will follow. For now, we ask you all to mark your calenders: The meeting will start with a dinner on Sunday, July 8, and end after lunch on Thursday, July 12. To all present nuClock members: This conference will include the internal nuClock yearly meeting 2018.

Looking forward to see you all at the conference!

The currently most accepted value of the isomer energy is 7.8(5) eV, obtained by the so-called “Beck et al. measurement”. In this experiment, researchers from Lawrence Livermore employed a NASA microcalorimeter for a high-resolution gamma measurement of the U-233 decay. Using a clever differencing scheme, they indirectly inferred the energy of the isomer. The final result includes correction terms related to unknown branching ratios.

This measurement is now 10 years old, and in the meantime, no experiment was successful in refining the isomer energy further (there is evidence from the LMU experiment, however, that the isomer energy is between 6.31 and about 18 eV). In particular, two independent experiments at PTB in Germany and UCLA/ALS searched for an optical signal of the isomer using synchrotron radiation to excite nuclei on/in wide bandgap materials, but found no signal. E. V. Tkalya et al. were the first to revisit the Beck et al. measurement and showed that branching ratios markedly different from the ones assumed in the original publication would lead to an isomer energy much larger than 7.8 eV (see their paper here).

Many current experiments have a limited search window, contrained e.g. by the ionization thresholds of Th ions or the transmission window of crystals. Inspired by the mysteriously short lifetime of the Th+ isomer in the LMU experiment, the TU Wien team set out to re-evaluate the original Beck et al. data, aiming to check if the 2007 measurement would be compatible with a much higher isomer energy. Their analysis is now available on the arXiv.

The authors find no major flaw in the original 2007 data analysis. They expand the statistical error of 0.5 eV, which appears to be underestimated, into a two-dimensional contour plot, constructing confidence regions for any given branching ratio. They find that the isomer energy depends only mildly on the branching ratio, in contrast to an earlier analysis by S. L. Zakharov. To give a rough estimate, an isomer energy above 10 eV (below 125 nm) can be excluded at the 95% confidence level.

If you have comments and would like to join the discussion, please share your thoughts with us!