Each new isotope that is discovered is a chance to study a mixture of protons and neutrons that has never before been seen. At the edges of the chart of nuclides, even the smallest piece of information on a new isotope could impact how we think about nuclear structure. In a recent experiment performed at the 88-inch cyclotron facility, NSD’s Heavy Elements Group discovered a new isotope of mendelevium [1]. This isotope, ²⁴⁴Md, is the lightest isotope of mendelevium yet observed.

Typically, a new isotope is identified because its decay properties are different from those of other previously-observed isotopes. However, it is often the case that neighboring isotopes can have very similar decay properties and it can be difficult to confirm that a new isotope had been produced. In this measurement, researchers took advantage of the FIONA (for the identification of Nuclide A) apparatus to directly measure the mass number of the new isotope and to erase any ambiguity in its discovery. FIONA is a new addition to the 88-inch cyclotron facility and has recently made headlines for making the first ever direct mass number identification of a super heavy element [2].

In FIONA, ions take special looped trajectories that are dependent on their mass number. Ions with different mass numbers take different trajectories and arrive at different locations in the detector. In this measurement, FIONA was calibrated with ions of astatine isotopes and then setup such that mass-244 ions of ²⁴⁴Md would arrive for detection at the same position as ions of ¹⁹⁸At. As Fig. 2 shows, the produced ions of mendelevium arrived where ions of mass number 244 were expected. This gives direct confirmation that a new isotope of mendelevium with mass number 244 has been discovered.

The half-life of the new isotope was measured to be roughly 0.4s, in agreement with theoretical calculations that assume this isotope decays primarily through alpha-particle emission. Given this information researchers believe it is unlikely that ²⁴⁴MD has a large beta-decay branch.

The Heavy Elements Group is now preparing similar experiments to search for even more isotopes on the edge of the nuclidic chart.

References
[1] J. L. Pore, J. M. Gates, R. Orford, et al., “Identification of the new isotope ²⁴⁴,” Physical Review Letters 124, 252502 (2020).
[2]. J. M. Gates, G. K. Pang, J. L. Pore, et al., “First Direct Measurements of Superheavy-Element Mass Numbers,” Phys. Rev. Lett. 121, 222501 (2018).