Pushing the limits of the periodic table

Pushing the limits of the periodic table

By GINA STAFFORD The Knoxville News-Sentinel

KNOXVILLE, Tenn. (June 6, 1999 11:14 a.m. EDT http://www.nandotimes.com) - King Arthur had a holy grail; Witek Nazarewicz has his "magic nuclei."

Nazarewicz is a theoretical physicist in search of elements with atoms that are stable yet jam-packed with protons and neutrons in their nuclei. Because of their potential atomic weight, they're called "the super heavies."

In his quest for them, Nazarewicz, of Oak Ridge National Laboratory and the University of Tennessee, has taken a major step forward. He may have helped identify a new element to be added to the periodic table: No. 114, for the record, called "ununquadrium " for now.

Holding degrees from Warsaw University of Technology, Nazarewicz is a native of Poland whose enthusiasm for his science is obvious. During an interview he pulled out a handful of charts and scribbled diagrams on paper to illustrate the principles behind the potential breakthrough.

"The data are not 100 percent conclusive, of course, but what we have found is evidence for the possibility of a new element. The evidence came through a set of very complicated calculations. A super computer sweats for weeks and then you get a number from Europe," he said, smiling.

The team effort involved Nazarewicz and his ORNL colleagues, physicists at the Joint Institute for Nuclear Research in Dubna, Russia, and at California's Lawrence Livermore National Laboratory.

Last November and December, the physicists at Dubna and Lawrence Livermore spent 40 days bombarding plutonium targets with calcium ions. Until then, Nazarewicz said, scientists had believed that process would result in a reaction that would cause fission to occur before an element could be created.

Of the vast number - 10 to the 18th power, to be exact - of collisions created by running the experiment, "one decay chain stood out as a candidate to be a new element, No. 114," according to UT Physics Department officials.

Meanwhile, Nazarewicz and fellow researchers from Warsaw and Brussels, Belgium, had been working for years on mathematical models to determine the limits of atomic mass. Upon hearing of the possible element created by the experiment last fall, Nazarewicz and his team offered their models for comparison.

"What was found was remarkable agreement between our theory and their experiment," he said. "I felt great about it. I feel, thanks to our work, there's great confidence this is the stuff. It's very gratifying."

The milestone has been outlined in two papers - one from Dubna dealing with the experimental work, another from Nazarewicz and his colleagues on the theoretical side - submitted to the scientific journal, Physical Review Letters.

Nazarewicz said he expects the GSI group, "the German equivalent of our national laboratory system," to be among the first researchers who'll try to verify the work.

In scientific history, the "super heavies" mark a fourth period of radioactive element discovery, UT officials said.

The first period and beginning of this radioactive era brought the work of Marie and Pierre Curie. They launched the atomic age 100 years ago with their discovery that not all nuclei are stable - that some are radioactive. They also discovered polonium - No. 84 - named for Poland, Marie Curie's native country.

The Curies' discoveries led physicists to wonder what the limits of charge and mass for a nucleus might be. Scientists found that by manipulating the numbers of protons and neutrons, they could synthesize elements in laboratories.

Which is what went on during the second period of radioactive element discovery, marked by the Manhattan Project, during which plutonium - No. 94 - took its place on the periodic table. The third time period was essentially the Cold War competition waged between Russian laboratories at Dubna and American labs in Berkeley, Calif., for the discovery of new elements.

The current, or fourth, period has been dominated by work in Darmstadt, Germany, which Nazarewicz said has been the source of the six new elements found since 1981.

That year, Bohrium - No. 107 and named for Danish physicist Niels Bohr - became the first member of the "super heavy" class, Nazarewicz said.

"From that up to 112, all belong to the Germans. Then the Germans ran out of steam - even the Germans," he said and laughed. "Actually, they had approached the limits of their technical capability."

From element No. 112 to No. 114, a "dramatic jump" - from microseconds to 30 seconds - in the elements' half-lives were found, Nazarewicz said.

"For some, the question of existence may mean years or ages, but for me, if something exists for a second, this is a long time," he said. "That half-life of 30 seconds is fairly long."

And what are these elements? Do they occur in nature?

"We don't know. That's hard to say," Nazarewicz said. "It may be that some cosmic explosions in space could be the source of the kinds of events necessary to produce them. I doubt they could be produced in massive amounts.

"But as we say in physics, 'Always expect the unexpected.' For those of us who are proud of being explorers, this is certainly the case."

The so-called magic nuclei Nazarewicz seeks are "the longest-lived super-heavy elements." Creating them means creating a blueprint for mapping out the nuclear landscape's uncharted territory, what he calls the "terra incognita" - "Or to see how far you can go in atomic mass - how heavy you can make the stuff."

No. 112 remains the last confirmed "super heavy," discovered in 1996. Like Nos. 110 and 111 before it, No. 112 remains unnamed "because of politics," Nazarewicz said. He said No. 113 might be a more difficult experiment to produce than No. 114 as the scientific world moves closer to their identification.

Naming disputes led the International Union for Pure and Applied Chemistry to develop a system based on Latin to issue temporary names based on individual numbers.

Clearly pleased at the accolades for working to identify "ununquadrium," Nazarewicz gets an even brighter twinkle in his eye as he talks of promise held by the future.

"Sometimes research doesn't have to have an immediate payback. Pure research by pure scientists has changed the world before," he said. "Look at the laser. That was a discovery by pure scientists. So was the transistor, and now those are everywhere."