Sailing toward the island of stability

Creation of six new superheavy isotopes encourages researchers

Chemists searching for the island of stability now have a better map. Thanks to the discovery of six new variations of the superheavy elements on the bottom rung of the periodic table, scientists are closer to creating elements that are expected to last long enough for in-depth study.

Researchers at Lawrence Berkeley National Laboratory in California saw the isotopes of rutherfordium, seaborgium, hassium, darmstadtium, and copernicium by watching the decay of the yet-to-be-named element 114, a synthetic element first produced about a decade ago. Each isotope of an element differs in the number of neutrons in its nucleus, a variable that can affect radioactivity and other properties.

The nuclear chemists created a sample of element 114 by bombarding a plutonium target with a beam of calcium ions. As the handful of atoms began to decay — a process that takes less than a tenth of a second — the team saw six previously undiscovered isotopes of other heavy elements, the researchers report in an upcoming issue of Physical Review Letters.

Heavy radioactive elements tend to decay quickly, most commonly by emitting an alpha particle — two protons and two neutrons, the nucleus of a helium atom. Researchers saw element 114 spit out alpha particles in a chain, creating isotopes of elements 112, 110, 108, 106, and 104 — with 169, 167, 165, 163 and 161 neutrons respectively.

Some of the isotopes are living longer, or have a longer half-life, than previously observed superheavy elements. One isotope of element 114 lasts 2.7 seconds before decaying — an “eternity,” says Heino Nitsche, a nuclear chemist at Lawrence Berkeley.

Scientists believe that certain combinations of protons and neutrons in a superheavy element’s nucleus would place it in an “island of stability” where radioactive decay would be substantially slower than in the superheavy elements discovered so far (SN: 6/5/10, p. 26). The new isotopes may help guide theorists to a better understanding of just where that island lies.

“The half-lives are picking up in a fashion that’s pretty encouraging,” says chemist Paul Karol at Carnegie Mellon University. “If they actually find something and they live long enough, it means they can do some chemistry on it, which brings it back to the world we can actually see.”

The isotopes don’t behave quite as expected — some decay more readily, some less willingly, than the leading theoretical model predicts. The discrepancies mean something isn’t quite right with the theory that predicts how atoms behave as they are synthesized heavier and heavier.

“The theories don’t describe the nucleus. This will give a fundamental improvement of understanding of the nucleus,” says Nitsche.

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