Island of Stability - Discovering New Superheavy Elements

Understanding the Island of Stability in Chemistry

The island of stability of the elements (circled) is predicted based on the half-lives of isotopes. Measured half-lives are in boxes, while predicted half-lives are shaded.
The island of stability of the elements (circled) is predicted based on the half-lives of isotopes. Measured half-lives are in boxes, while predicted half-lives are shaded.

The island of stability is that wondrous place where heavy isotopes of elements stick around long enough to be studied and used. The "island" is located within a sea of radioisotopes that decay into daughter nuclei so quickly it's difficult for scientists to prove the element existed, much less use the isotope for a practical application.

History of the Island

Glenn T. Seaborg coined the phrase "island of stability" in the late 1960s. Using the nuclear shell model, he proposed filling the energy levels of a given shell with the optimal number of protons and neutrons would maximize binding energy per nucleon, permitting that particular isotope to have a longer half-life than other isotopes, which did not have filled shells. Isotopes that fill nuclear shells possess what are called "magic numbers" of protons and neutrons.

Finding the Island of Stability

The location of the island of stability is predicted based on known isotope half-lives and predicted half-lives for elements that have not been observed, based on calculations relying on the elements behaving like those above them on the periodic table (congeners) and obeying equations that account for relativistic effects.

The proof that the "island of stability" concept is sound came when physicists were synthesizing element 117. Although the isotope of 117 decayed very quickly, one of the products of its decay chain was an isotope of lawrencium that had never been observed before. This isotope, lawrencium-266, displayed a half-life of 11 hours, which is extraordinarily long for an atom of such a heavy element. Previously known isotopes of lawrencium had fewer neutrons and were much less stable. Lawrencium-266 has 103 protons and 163 neutrons, hinting at as-yet-undiscovered magic numbers that may be used to form new elements.

Which configurations might possess magic numbers? The answer depends who you ask, because it's a matter of calculation and there's not standard set of equations. Some scientists suggest there might be an island of stability around 108, 110, or 114 protons and 184 neutrons. Others suggest a spherical nucleus with 184 neutrons, but 114, 120, or 126 protons might work best. Unbihexium-310 (element 126) is "doubly magic" because its proton number (126) and neutron number (184) are both magic number. However you roll the magic dice, data obtained from the synthesis of elements 116, 117, and 118 point toward increasing half-life as the neutron number approached 184.

Some researchers believe the best island of stability might exists at much larger atomic numbers, like around element number 164 (164 protons). Theorists are investigating the region where Z = 106 to 108 and N is around 160-164, which appears sufficiently stable with respect to beta decay and fission.

Making New Elements from the Island of Stability

Although scientists might be able to form new stable isotopes of known elements, we don't have the technology to go much past 120 (work which is currently underway). It's likely a new particle accelerator will need to be constructed that would be capable of focusing onto a target with greater energy. We'll also need to learn to make larger amounts of known heavy nuclides to serve as targets for making these new elements.

New Atomic Nucleus Shapes

The usual atomic nucleus resembles a solid ball of protons and neutrons, but atoms of elements on the island of stability may take new shapes. One possibility would be a bubble-shaped or hollow nucleus, with the protons and neutrons forming a sort of shell. It's hard to even imagine how such a configuration might affect the properties of the isotope. One thing is certain, though... there are new elements yet to be discovered, so the periodic table of the future will look very different from the one we use today.

Key Points

  • The island of stability refers to a region of the periodic table consisting of super-heavy radioactive elements that have at least one isotope with a relatively long half-life.
  • The nuclear shell model is used to predict the location of the "islands," based on maximizing the binding energy between protons and neutrons.
  • Isotopes on the "island" are believed to have "magic numbers" of protons and neutrons that allow them to maintain some stability.
  • Element 126, should it ever be produced, is believed to have an isotope with a long enough half-life that it can be studied and potentially used.