Two new elements are heaviest yet seen

Short-lived substances made using atom smasher

June 09, 1999|By SAN FRANCISCO EXAMINER

BERKELEY, Calif. -- Berkeley scientists have discovered two new elements, the heaviest ever seen.

Dubbed 116 and 118, they were created inside a cyclotron, or atom smasher, at the Lawrence Berkeley National Laboratory. They're as fleeting as a discovery can be, though: Each lives only a moment. Then, within a tiny fraction of a second, they decay into subatomic fragments and pure energy.

At the lab, people are very excited by the discovery that involves a team led by physicist Ken Gregorich.

"A huge amount of effort has gone into it," said Claude Lyneis, an accelerator physicist who runs the 88-inch cyclotron where the discovery was made.

Lyneis said the lab decided to announce the discovery after rumors of the achievement began to appear on academic Web sites.

The discovery marks a major step toward one of nuclear physicists' goals: a hypothetical "island of stability" of super-heavy elements that might last for many years, rather than instantly decaying. The heaviest element found in sizable amounts in nature is uranium, with the atomic number 92. (The number refers to the number of protons, the positively charged particles of the atomic nucleus, in an element.)

Physicists who study the nuclear structure of atoms have been seeking super-heavy elements for decades. They dreamed of finding super-heavy elements in the "island of stability" that might endure for billions of years.

In the 1970s, Berkeley scientists entered a Bay Area Rapid Transit tunnel to look for radiation from hypothesized super-heavy elements in the geological layers. They looked there because the purported elements' radioactive signals would be easier to detect than on the surface, where background radiation from cosmic rays and other sources constantly confuses instruments.

But they found nothing, said physicist Darleane Hoffman of Lawrence Berkeley.

So they tried to create the elements by bashing together high-speed particles inside accelerators. So did physicists working in Russia, who previously said they had created -- in collaboration with scientists from Lawrence Livermore National Laboratory east of San Francisco -- element 114. However, the Russian-Livermore claim is based on a single observation and is not proved, Lawrence Berkeley scientists maintain.

By contrast, the discovery of 116 and 118 is based on the Lawrence Berkeley scientists' observations of three separate decays of the elements in the cyclotron, Lyneis said. Element 118 decays into 116, then into smaller products.

Hence, he said, "it looks like we've landed on the edge of the island of stability, or on the shore."

Hoffman said old hopes of finding super-heavy elements that last a billion years or so have faded. Nowadays, optimists hope to find super-heavy elements that last about a century.

Does the discovery have practical applications? Hoffman recalled the words of the Lawrence Berkeley Nobel laureate Glenn Seaborg, who died early this year after a career that included the synthesis of the element plutonium, used in nuclear weapons.

"We cannot very often predict the practical applications of basic science," Seaborg said, "but we can predict that those practical applications will occur to the enduring benefit of man."

Pub Date: 6/09/99

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