The facility for rare isotope beams observes five never-before-seen isotopes

The Science

The first search for new isotopes at the Facility for Rare Isotope Beams (FRIB) discovered five never-before-seen heavy element isotopes: thulium-182 and 183, ytterbium-186 and 187, and lutetium-190. Researchers found the new isotopes in the debris of collisions between a stable beam of platinum-198 and a carbon target. The challenge was not to produce these new nuclei but to distinguish them from the hundreds of known nuclei that were produced at the same time, then to precisely identify their mass and charge.

The Impact

These results promise an exciting future and give a glimpse of the scientific reach for the study of heavy rare isotopes. Heavy nuclei are notoriously difficult to separate and identify but they are important for understanding the cosmic production of more than half of the elements heavier than iron. This search for new isotopes succeeded less than one year after FRIB began operating. FRIB continues to increase its capability. The facility now produces beams more than six times as intense as at the time of the measurement, bringing nuclei in reach that can help researchers understand the elemental fingerprint of the universe.

Summary

The five previously unobserved isotopes—thulium-182 and 183, ytterbium-186 and 187, and lutetium-190—were produced, separated, and identified for the first time in the Advanced Rare Isotope Separator (ARIS) at FRIB. Researchers formed the new isotopes in the projectile fragmentation of a platinum-198 beam on a rotating carbon target. They identified these isotopes for the reaction products using measurements of the energy loss, time of flight, momentum, and total kinetic energy. The novel two-stage design of ARIS provided the high resolving power needed to suppress the more abundant, less neutron-rich contaminant species.

This work demonstrates the discovery potential of FRIB, which will eventually provide two orders of magnitude more beam current than it now offers. In addition, while not quite reaching nuclei that inform nucleosynthesis in stellar processes, the present results show that there are no barriers for producing, separating, and identifying the heavy neutron-rich isotopes in the relevant region of the nuclear chart. This work was performed by a collaboration of scientists from the United States, Japan, and South Korea.

Funding

This material is based upon work supported by the Department of Energy Office of Science, Office of Nuclear Physics, the National Science Foundation, and the Institute for Basic Science in South Korea.