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Back on the Table? Element 118 is served up again.

New research suggests that the periodic table may once again reach 118. A team of nuclear chemists from the United States and Russia has announced the brief appearance of the unnamed element, the heaviest to date.

A report of element 118 had made a splash before. In 1999, a group at Lawrence Berkeley (Calif.) National Laboratory claimed that it had created the element by bombarding lead with krypton ions (SN: 6/12/99, p. 372). But the researchers retracted the finding 2 years later (SN: 8/4/01, p. 68), after other labs couldn't reproduce the results.

The new work synthesized element 118 from different materials--an isotope of californium and calcium ions. During each of two several-months-long experimental runs, the research team pummeled the californium with 10 million trillion calcium ions, says Mark A. Stoyer of Lawrence Livermore (Calif.) National Laboratory, which partnered with the Joint Institute for Nuclear Research in Dubna, Russia, for the project.

Three times--once in the first run in 2002 and twice in the second run in 2005--atoms of californium and calcium combined to form the new element, which contains 118 protons and 176 neutrons.

Each of the three atoms of element 118 remained on the scene for just under one-thousandth of a second. The element then decayed to element 116, then to element 114, and finally to element 112 before splitting in two, says Lawrence Livermore team member Dawn A. Shaughnessy.

At this point, the data "look good," comments Kenneth E. Gregorich, a nuclear chemist at Lawrence Berkeley. "The decay properties that they are measuring are as expected," he says. The results, published in the October Physical Review C, await independent confirmation.

The U.S. and Russian team had previously discovered elements 113, 114, 115, and 116. None of its experiments has been confirmed by an outside laboratory, although recent research by a Swiss team working at the Russian facility provides evidence for 114, notes Gregorich.

Element 118 resides near the so-called island of stability (SN: 2/6/99, p. 85), a group of heavy elements that theoretical physicists predict will have "magic numbers" of protons and neutrons that make them highly stable.

Some physicists expect that these heavy elements, if they exist, will persist for "hours or days or even a year," says Stoyer. "If you could find something that heavy and that long-lived, maybe you could find some more useful chemical properties," he says. "That's what excites people in this kind of work."

The U.S. and Russian team will next try to synthesize element 120, Stoyer says. When researchers can no longer cram protons into a nucleus, "that will be the end of the periodic table," he adds.
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Author:Cunningham, A.
Publication:Science News
Geographic Code:4EXRU
Date:Oct 21, 2006
Words:446
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