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Berkeley Crew Bags Element 118
7 June 1999 8:45 pm
Step aside, element 114; there's a new heavyweight champ. Physicists at the Lawrence Berkeley National Laboratory in California announced today that they have created two new superheavy elements, tipping the scales at 118 and 116 protons each.
Ever since the early 1940s, when scientists created the first handful of artificial elements beyond the 94 that exist in nature, physicists have vied to forge the next heaviest element. A milestone came last January when researchers at the Joint Institute for Nuclear Research in Dubna, Russia, working with Lawrence Livermore National Laboratory (LLNL), created the long-sought element 114. That element's relatively long 30-second lifetime seemed to confirm predictions of an "island of stability"--a realm of superheavy elements, including 114, that would be more stable than heavier and lighter isotopes.
That Russian-LLNL team accomplished their feat using a technique known as hot fusion, in which a beam of light isotopes is smashed into a heavier target, such as plutonium. Previously, the technique of choice was a gentler collision of medium sized isotopes called cold fusion; conventional theories suggested that forging elements 116 and 118 this way would be too much of a long shot. But the prospects for hot fusion didn't look much better, because the higher energy technique is more likely to create nuclei that would immediately fission, or split in half, making it impossible to track them.
The Berkeley team's big break came after Robert Smolanczuk, a visiting theorist from the Soltan Institute for Nuclear Studies in Poland, offered calculations suggesting that bombarding a lead target with krypton ions--a cold-fusion technique--would have reasonable odds of producing a few atoms of 118 that wouldn't fission immediately. "We didn't really believe it," says Ken Gregorich, who led the 15-member Berkeley team. "But it was one of those experiments where there was little to lose and a big upside."
But Smolanczuk was right. During 11 days of flinging krypton ions into the lead and sifting through the impact debris, the team three times observed a distinct pattern of alpha particle emissions--the particles element 118 shed in search of a more stable configuration. As an added bonus, the first alpha decay in each case produced an atom of element 116--also never before seen.
"It's a very exciting result," says LLNL heavy element physicist Ron Lougheed. "I suspect it will lead to a flurry of new isotopes in this region." Next up, Gregorich says, his team will switch the lead target for one of bismuth, which has one extra proton. Their goal, of course: element 119.