The New York Times
In a discovery that came as a complete surprise to most nuclear chemists, an iternational team of scientists at Lawrence Berkeley National Laboratory in California has addad two new elements to the periodic table.
The laboratory announced Monday that the two elements, with atomic numbers 118 and 116 on the periodic table, were created in late April using a cyclotron accelerator to bombard a lead target with projectiles of krypton atoms. In three of the collisions observed by the Berkeley team, target and projectile atoms fused to form gigantic atoms with nuclei containing 118 protons and 175 neutrons.
Each of the atoms of Element 118 survived for less than 1/10,000 of a second before decaying radioactively into an atom of a second new element, Element 116, with 116 protons and 173 neutrons in its nucleus.
Until this experiment, the fusion route by which Element 118 was created was considered impossible by most of the scientists involved in heavy-element research, including those at Germany's Society for Heavy Ion Research, in Darmstadt, and Russia's Joint Institute for Nuclear Research, at Dubna.
However, a young Polish theorist, Dr. Robert Smolanczuk, made a series of calculations from which he concluded that a lead-and-krypton collision technique could produce the desired element.
"But no one, including the people at GSI where Robert was working believed it," said Al Ghiorso of the Berkeley laboratory, who is himself one of the world's leading discoverors of new elements.
Although Smolanczuk's calculations were at odds with prevailing theories of possible routes to heavy artificial elements, the Berkeley laboratory resolved to try them out, using krypton atoms containing 86 protons to bombard lead atoms with 208 protons. A speccial detector, the design for which was proposed by Ghiorso, measured the debris produced when a single ephemeral atom of Element 118 decayed in a chracteristic way.
The Berkeley experimental team, headed by Dr. Kenneth Gregorich, measured the atom's decay into Element 116, then 114, then 112 and on down to 106-- an artificial element that was recently named seaborgium in honor of the late Dr. Glenn Seaborg, the chemist who discovered plutonium.
All elements containing more than the 92 protons in the nucleus of a uranium atom are called "trasuranic" elements, and none exists in nature in appreciable quantities. Most are so radioactive that they decay swiftly. Some have practicle uses. Plutonium fuels nuclear weapons. Americium is used in smoke detectors, and several transuranic elements are used in nuclear medicine.
[THE ABOVE QUOTED ARTICLE APPEARED IN THE PROVIDENCE JOURNAL, THURSDAY, JUNE 10, 1999.]
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