Scientists in California and Russia announced yesterday that they have created the heaviest atomic element ever made, adding a new item to the universal menu of matter known as the periodic table and revealing fresh secrets about the nature of atoms, the fundamental units of physical stuff.

The new, radioactive element, which has not yet been formally named but is being referred to variously as ununoctium (Latin for "one-one-eight"), eka-radon (beneath radon on the periodic table) or simply element 118, did not linger long.

Indeed, as with most "super-heavy" elements -- which are not known to exist in nature but have been synthesized by slamming smaller atoms together -- the three atoms of ununoctium created in the latest experiments came and went in a literal flash.

But during their brief tenures of about nine ten-thousandths of a second each in a laboratory on Russia's Volga River, those three atoms revealed much about the laws that govern the behavior of matter, scientists said.

And while practical applications for such fleeting phenomena are difficult to envision, experts said they were confident some would appear -- especially if researchers can leverage the findings to make even larger atomic constructs that might have lifetimes of minutes, months or longer.

"One never knows what the application of the things you find may be," said Darleane Hoffman, a professor of chemistry at the University of California at Berkeley, tossing out the example of plutonium-239, the key fissile ingredient in atomic bombs, first created in 1941.

Physicists cautioned that the finding must be considered provisional for now. That is true of all experiments that have yet to be independently replicated, but especially so for the finding of element 118, whose discovery was first reported by a Berkeley team in 1999 and then retracted two years later when it became clear that the results were fraudulent.

The last new element to be confirmed was No. 111, roentgenium, discovered in 1994.

But scientists involved in the new find -- and others who reviewed the report, published in the October issue of the journal Physical Review C -- said they were virtually certain that what they saw in that millimoment was indeed a microhunk of ununoctium.

"I would say we're very confident," said team member Nancy Stoyer of the Lawrence Livermore National Laboratory in Livermore, Calif., estimating that the odds of the result being false were less than 1 in 10,000.

The team was led by Dawn Shaughnessy of Livermore and Yuri Oganessian of the Joint Institute for Nuclear Research in Dubna, Russia.

Every naturally occurring thing in the universe is made from a modest celestial palette of 92 elements, from hydrogen to uranium. Each element has an atomic number (from 1 to 92) representing the number of positively charged protons in that atom's core, or nucleus. Many variants, or isotopes, of each element also exist through the addition of varying numbers of uncharged neutrons to those nuclei.

For decades, scientists have been making new elements, heavier than any found in nature, in part to help them understand the basic forces that hold atoms together and keep them apart. They also want to know the biggest element that can be made. Theory predicts a finite limit.

The technique involves spraying a target made of one kind of atom with atomic buckshot of another kind and hoping that a few of the incoming nuclei will hit a few of the target atoms with enough force to overcome their mutually repulsive positive charges and merge into one giant nucleus, at least briefly. To accomplish that requires a combination of ultra-precise engineering and outlandish brute force.

In the latest experiments, which took more than 3,000 hours, the researchers fired about 40 billion billion atoms of calcium-48 -- a heavy, neutron-laden version of calcium -- at a target of californium-249, a highly radioactive synthetic element. Special sensors detected a total of three atoms of ununoctium flying off as a result of those painstaking efforts -- one in an experiment in 2002, and two in early 2005.

Each quickly threw off a pair of protons and a pair of neutrons to make element 116, then did so again to make element 114, and again to make element 112, which then split in two.

It is that trail of "daughters" that allows scientists to infer that a "mother" atom was there in the first place. But that kind of proof is tricky, said Walter Loveland, a chemistry professor at Oregon State University, because the super-heavy daughters are so poorly understood themselves.

Still, Loveland said he found the results "impressive and internally very self-consistent" and "a tremendous intellectual achievement."

One major question left unanswered by the experiment is whether there are super-heavy elements yet to be made that will be far more stable -- a predicted phenomenon that scientists have called "an island of stability."

An isotope of element 114, discovered by Livermore scientists, showed preliminary but now uncertain evidence of unusual longevity, on the order of 20 seconds. Some had predicted that ununoctium might stick around long enough for researchers to do some chemistry on it. The new work, while undermining that idea, offers new information that will help theoreticians revamp their predictions, which can then be tested by experimentalists.

"We're nibbling away at the shores of the island of stability," said Livermore's Ken Moody.