New atomic nucleus found — far from stability


Where does the world of atomic nuclei end? Scientists went further into the region of unstable elements than ever before. An experimental collaboration at the fragment separator of the GSI Helmholtzzentrum für Schwerionenforschung has for the first time detected potassium-31, an isotope with eight neutrons less than the stable potassium atom. An atomic nucleus that remote from stability has never been observed before. The results were published in the journal Physical Review Letters.

It is an exotic atomic nucleus that lies further outside the proton dripline than has ever been observed before: Potassium-31 is extremely short-lived with a half-life below nanoseconds, but the sheer existence of the atomic nucleus is a new record. In physics, the proton dripline marks a boundary beyond which we find the unbound atomic nuclei. Due to the unbalanced ratio of neutrons and protons, they can hardly exist and decay very quickly. Potassium-31 is four neutrons far outside this dripline. An atomic nucleus that remote from the proton dripline has never been observed before.

The exotic isotope of potassium was produced by the particle accelerator facility on the GSI/FAIR campus. The ring accelerator SIS18 and the fragment separator (FRS) in combination provided a secondary particle beam of argon-31 which again was shot at a beryllium target. In this way, the research team succeeded in producing potassium-31. Daria Kostyleva, who is currently working on her PhD thesis at GSI, FAIR and the University of Gießen, analyzed the data from the fragment separator experiment and carried out simulations. "We haven't reached the border between unbound systems and chaotic nuclear matter yet," she says. "There could be atomic nuclei that are up to seven neutrons away from the proton dripline. We want to test whether the main nuclear structure principles still apply there."

These chaotic systems could be found in the future at the new FAIR particle accelerator facility. The detectors with which the discovery was made are part of the experiment program of the Super fragment-separator (Super-FRS) which will be operated at FAIR and is part of the large-scale experimental collaboration NUSTAR. Thanks to FAIR's much more intense particle beam and the higher energies that can be achieved, scientists expect to discover many new isotopes. The experiments studying remote proton-unbound systems are being carried out within the EXPERT collaboration (EXotic Particle Emission and Radioactivity by Tracking) of Super-FRS. Scientists from GSI and FAIR, the University of Gießen, the Joint Institute for Nuclear Research in Dubna (Russia), the Silesian University in Opava (Czech Republic) and the University of Warsaw (Poland) are involved in the EXPERT experiments. (LW)

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