Two nuClock papers surfaced this week: On Monday, the conference proceedings of last year’s FS&M symposium in Potsdam appeared, with a contribution by the Vienna group (link). The proceedings are free to download.
Then on Tuesday, recent work on U-233 doped crystals appeared with Phys. Rev. C (link). This paper had kind of a rough start, cycling through half a dozen review rounds with nearly the same number of referees absorbed. Some of the referees’ remarks were not about the content itself, but rather as to whether the “Thorium topic” is interesting at all. Our most favorite comment by one of the referees (slightly rephrased here): “So a direct observation of the decay of the isomer and determination of its half-life are rather a technical challenge than a highlight in nuclear structure physics. (…) The paper should therefore be deferred to a more technical journal.“. Let’s recall that APS already did publish three “First observation of the thorium isomeric transition” papers, all of which turned out to be false very soon after… Read a beautiful comment by Reinhard Werner (link) very much along these lines.
The Phys. Rev. C paper explores a rather new idea to measure the isomer energy by optical spectroscopy, first mentioned a couple of years ago by Eric Hudson’s group (link to the paper). Past experiments used U-233 recoil nuclei adsorbed on a surface (but suffered from low count rates) or synchrotron radiation on crystals (but could never be sure if the isomer was populated at all). The new approach combines the benefits of these experiments: a reliable source of isomeric nuclei (U-233 decay) combined with a bulk crystal (effectively going from 2D to 3D). The expected count rate is orders of magnitude larger compared to experiments using the accumulation on surfaces, and might yield a signal within a few weeks of measurement time. Internal conversion is still expected to be the biggest spoiler, especially since the position or state of the Th-229m ion cannot be controlled.