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RESEARCH PRODUCT

Nuclear isomers in superheavy elements as stepping stones towards the island of stability

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The stability of an atomic nucleus is determined by the outcome of a tug-of-war between the attractive strong nuclear force and the repulsive electrostatic force between the protons in the nucleus. If 100 protons and about 150 neutrons or more are assembled into a nucleus, the repulsion usually becomes dominant and causes the nucleus to fission. For certain 'magic numbers' of protons and neutrons this repulsion can be overcome and the nucleus stabilized. In particular an 'island of stability' is predicted beyond the actinides, where long-lived or even stable superheavy elements can exist, but its precise limits are unknown. Experiments can help determine where this island lies, however. Spectroscopy of the nobelium isotope, 254No reveals three excited structures, two of them metastable. This finding will help to constrain nuclear models of the superheavy elements, and provides more data for the search for the next magic numbers. Spectroscopic studies of the nobelium isotope 254No — the heaviest nucleus studied in this manner to date — details three excited structures, two of which are metastable, which should help to constrain nuclear models of the superheavy elements. A long-standing prediction of nuclear models is the emergence of a region of long-lived, or even stable, superheavy elements beyond the actinides. These nuclei owe their enhanced stability to closed shells in the structure of both protons and neutrons1,2,3. However, theoretical approaches to date do not yield consistent predictions of the precise limits of the ‘island of stability’; experimental studies are therefore crucial. The bulk of experimental effort so far has been focused on the direct creation of superheavy elements in heavy ion fusion reactions, leading to the production of elements up to proton number Z = 118 (refs 4, 5). Recently, it has become possible to make detailed spectroscopic studies6,7 of nuclei beyond fermium (Z = 100), with the aim of understanding the underlying single-particle structure of superheavy elements. Here we report such a study of the nobelium isotope 254No, with 102 protons and 152 neutrons—the heaviest nucleus studied in this manner to date. We find three excited structures, two of which are isomeric (metastable). One of these structures is firmly assigned to a two-proton excitation. These states are highly significant as their location is sensitive to single-particle levels above the gap in shell energies predicted at Z = 114, and thus provide a microscopic benchmark for nuclear models of the superheavy elements.