Physicists Detect Rare 10+ Isomer in Ytterbium-150, Revealing Nuclear Isomeric Relay

A question that had gone unanswered for 40 years got a concrete response last month when an international team led by the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences reported the first observation of a long-lived 10+ nuclear isomer in ytterbium-150, one of the most neutron-deficient nuclei in that region of the chart. The findings were published in Physical Review Letters on February 26.

The core result is precise: the 10+ isomer in Yb-150 carries a measured half-life of 0.62 microseconds, and the team established its complete decay scheme. That combination, a confirmed spin-parity assignment, a clean half-life measurement, and a full decay pathway, is exactly what you need to say something definitive about nuclear structure this far from stability.

The experiment ran at the Accelerator Laboratory of the University of Jyväskylä in Finland, where the IMP team and their Finnish collaborators used the gas-filled recoil separator RITU to isolate the recoiling Yb-150 nuclei and deliver them to the GREAT spectrometer's focal-plane detector system. From there, high-sensitivity delayed γ-ray spectroscopy did the heavy lifting. That RITU-GREAT combination is well-suited to exactly this kind of problem: short-lived exotic nuclei produced in low cross-section reactions, where you need clean recoil separation and fast, efficient γ detection at the focal plane.

What makes this more than a half-life measurement is the theoretical picture that emerged alongside the experimental data. Through calculations of the underlying nuclear configurations, the researchers identified changes within the 10+ isomeric chain that they term an "isomeric relay" mechanism. Specifically, the results point to a configuration shift from two-neutron to two-proton states near proton number Z = 64, meaning the character of the 10+ isomers changes as you move along the chain toward the proton drip line. The isomer in Yb-150 extends that chain further into drip-line territory than had previously been confirmed.

The 8+, 10+, and 12+ isomers in this region of the nuclear chart have drawn attention precisely because of how persistent these high-spin traps are as you push toward the limits of nuclear binding. The 40-year framing in the press materials reflects how long the community has tracked these states without being able to answer whether the chain continues all the way to the proton drip line. With Yb-150 now characterized, the chain is longer than it was a month ago, and the isomeric relay interpretation gives theorists a specific mechanism to test against other neutron-deficient nuclei in the same neighborhood.

The paper in Physical Review Letters is the place to dig into the full decay scheme data, the γ-ray energies and intensities, the branching ratios, and the details of whichever theoretical model the team used to arrive at the Z = 64 configuration-shift picture. The press materials confirm the result but leave those specifics to the journal. For anyone working on high-spin isomers near the proton drip line or trying to benchmark shell-model calculations in the A ~ 150 neutron-deficient region, that paper is worth pulling immediately.