A team of Russian and American scientists said yesterday that it had created the heaviest element ever seen in a laboratory, a dab of matter that lasted for less than one-thousandth of a second but would add an entry at the farthest reaches of the periodic table and suggest that strange new elements may lie beyond.
By convention, the substance remains the Baby Doe of elements until its existence is confirmed at other laboratories. For now, the new substance will be principally known as element 118 for the number of protons in its nucleus, more than in any other element occurring naturally or produced in the laboratory.
Hydrogen, the lightest element, has one proton in its nucleus, and uranium, the heaviest naturally occurring element, has 92. Element 118 would fit comfortably just below radon in a column of the periodic table containing what are called noble gases for their inert chemical properties.
The results were met with praise but also caution from other scientists in the field, particularly given the fraught history of element 118. Another California lab, the Lawrence Berkeley National Laboratory, announced that it discovered the element in 1999 but retracted the claim two years later after an investigation found that one of its researchers, Dr. Victor Ninov, had fabricated data. Dr. Ninov was later fired.
Dr. Ken Moody, the lead American researcher on the work, said everything had been done to guard against fabrication, with independent analyses being carried out in Russia and the United States. And the group’s paper on the putative find has been accepted at a prestigious journal, Physical Review C, after other scientists reviewed the work, said Dr. Jonathan Lenaghan, an editor at the journal.
But it was less the fear of fraud than ordinary scientific caution that caused some scientists to reserve judgment on the discovery. The Russian lab and its collaborators have now announced the discovery of five elements — 113, 114, 115, 116 and now 118 — none of which have been confirmed by other scientists.
“One has to be extremely careful with those enthusiastic announcements,” said Dr. Witold Nazarewicz, a nuclear theorist at the University of Tennessee and the Oak Ridge National Laboratory.
“This is not because one is doing something wrong,” Dr. Nazarewicz said. “It’s because these are very difficult measurements. They are playing on the edges of statistics.”
The team that created the element, made up of scientists at the Lawrence Livermore National Laboratory in California and the Joint Institute for Nuclear Research in Dubna, Russia, said they had produced three atoms of the new element in six months of smashing lighter elements together and trying to make them stick.
The scientists said their results also gave hope that they were approaching a long-predicted “island of stability” of even heavier elements, with longer lives and possibly strange new chemical properties.
“This considerably expands the borders of the existing material world,” Dr. Yuri Oganessian said in an e-mail message. He is the scientific director of the Flerov Laboratory of Nuclear Reactions at the Dubna institute, where the experiments were carried out in a cyclotron, the circular particle accelerator.
A Livermore scientist, Dr. Nancy J. Stoyer, said the team had calculated that there was less than one chance in 100,000 that the results were a statistical fluke.
“We’re very confident,” Dr. Stoyer said.
Other experimental scientists said nothing was obviously amiss with the work.
“I think the evidence they have is convincing,” said Dr. C. Konrad Gelbke, director of the National Superconducting Cyclotron Laboratory at Michigan State University. “It looks pretty good.”
The experiments were performed when scientists at the Russian laboratory used the cyclotron to bash atoms of calcium, with 20 protons, into a target of Californium, with 98 protons, like little clumps of putty that they hoped would stick together, said Dr. Dawn A. Shaughnessy, another Livermore scientist who worked on the experiment.
In extremely rare instances, they did stick. In 10 billion billion bombardments, detectors found that the two sets of protons glommed together to produce element 118.
An element’s weight is determined by the total number of protons, which have a positive electrical charge, and neutrons, which are neutral, in its nucleus.
By that measure, too, the new element is the heaviest ever created.
Dr. Gelbke said that there was one good reason that the Russian laboratory might be ahead of its competitors elsewhere in the world. Scientists at that lab, he said, are skilled in handling Californium, which is very radioactive and dangerous to the uninitiated.
“I wouldn’t want to do that myself,” Dr. Gelbke said, chucking. “It’s a fairly nasty substance for most people to handle.”
If the results are confirmed, they would represent one more step toward the “island of stability” that theorists have predicted in even heavier regions of the periodic table. Nuclei have shell-like structures, and the most stable atoms contain so-called “magic numbers” of protons and neutrons that produce closed, or complete, shells.
The numbers 2, 8, 20, 28, 50 and 82 are magic for both protons and neutrons. The highest known magic number for neutrons alone is 126, meaning that common lead, with 82 protons and 126 neutrons, is the heaviest known “doubly magic,” or extremely stable, isotope in the periodic table.
But the theorists have predicted that there is another closed shell out beyond all elements discovered so far, including the latest one.
“It’s rather like Plum Island at the end of Long Island,” Dr. Martin Blume, the overall editor of Physical Review, said. “You go there, there’s a gap, and then there’s Plum Island.”
There is general agreement that the next neutron magic number is 184. But that is still out of reach of current experiments.
The next proton magic number is a matter of disagreement.
“That is, I think, the basis for looking in this region,” Dr. Blume said. “Have you reached the island of stability?”