Periodic Table Grows By Two

Russian and American scientists say they have created two new "superheavy" elements that will reside at the extreme end of chemistry's periodic table of elements.

Just a few atoms of the newly discovered elements, 113 and 115, existed for split seconds after being created in a particle accelerator. They represent unusual forms of matter with properties that go well beyond those of the 92 elements that occur naturally on Earth.

Superheavies may be abundantly generated by supernova explosions in stars. Or perhaps they were fused during the fiery moments that signaled the dawn of the universe.

Here on the ground, such tiny amounts of superheavies formed in atom smashers probably will never find an everyday use.

Yet their "birth" adds details to a broader — and very competitive — scientific inquiry to establish a single, unified theory that would explain the physical forces that govern the behavior of all matter.

Data on the new elements will appear in the journal Physical Review C, a publication of the American Physical Society that specializes in nuclear structure.

The discoveries will not be fully accepted and added to textbooks until other labs create the elements, a process that could take months or even years.

Confidence in nuclear structure experiments was shaken when the purported 1999 discovery of two elements was found to be false. But other researchers familiar with the latest study said they were confident in the results.

"The paper is solid," said Richard Casten, a Yale physicist and an editor for the journal.

He described the techniques employed at the Joint Institute of Nuclear Research in Dubna, Russia, and the Lawrence Livermore National Laboratory in California as "very tricky."

But Casten and others expressed confidence in the results and the scientists involved, especially Yuri Oganessian, the Russian physicist and lead author of the paper, for being able to interpret the results of the particle collisions in the Russian cyclotron, or circular accelerator, where the elements were created.

"I'm confident that the process was good," Casten said. "Yuri is a very well respected and careful guy."

Oganessian said in a telephone interview that the newly discovered Element 115 existed for 80 milliseconds before decaying to Element 113. Element 113 then decayed to known elements, and one of them, Element 105, Dubnium, existed for 20 hours before it split, he said.

"The experiment has attracted huge attention," Oganessian told The Associated Press. "But we have just had the first and only experiment. A single result doesn't make a discovery. We must conduct a whole series of further experiments."

"I hope that other laboratories will also work on the subject," Oganessian added. "There are laboratories in the United States, Germany and Japan which can repeat it and go further. As of today, this is just a single fact which needs to be confirmed."

In the experiments, researchers fired a rare isotope of calcium at a target made from americium. The new element 115 was created on occasions when the nuclei of the calcium and americium fused.

In the artificial environs of the cyclotron, atoms of element 115, now labeled Ununpentium, apparently lasted only a fraction of a second before it decayed into element 113. The atoms of element 113, known as Ununtrium, persisted for more than 1 second.

The 115 and 113 are the new elements' atomic numbers, which refer to the number of protons in their nuclei.

In nature, scientists theorize, they would belong to a special class of superheavy elements known as the "region of stability" that have a much longer life because the shell-like structure of their nuclei contain the highest numbers of precisely arranged protons and neutrons.

In 1999, California and Oregon State University researchers bombarded a lead target with a beam of krypton ions. They reported detecting three atoms of element 118, which then was the heaviest element detected. They decayed almost instantly into element 116.

But two years ago, the claims were retracted after a scientist at the Lawrence Berkeley National Laboratory was found to have fabricated data. Physicist Victor Ninov was the only member of the lab's 16-member team to be dismissed in the incident, and he is appealing the decision.

Other researchers later created element 116.

In 1999, Russian researchers at Dubna discovered another superheavy — element 114 — by bombarding plutonium with calcium ions.