Two new "super-heavy" chemical elements have likely been discovered by scientists at Lawrence Livermore National Laboratory and in Russia.

The achievement, announced Monday, offers a closer glimpse of an exotic, long-hypothesized domain at the outer reaches of the periodic table of elements in which inherently unstable elements might survive long enough to yield new insights into the underlying fabric of matter.

The periodic table, the checkerboard-like chart that hangs in every chemistry classroom, depicts both known elements and those that haven't been discovered or created yet.

The elements vary mainly according to their number of protons, particles with a positive charge. For example, the lightest element, hydrogen, has one proton, helium has two, etc. The new elements, 113 and 115, are so named because each has that many protons.

In the 20th century, scientists figured out ways to create artificial elements that, as far as anyone knows, have never before existed anywhere on Earth. Unfortunately, most of these new elements decay into subatomic debris very quickly, sometimes in fractions of a second; hence they're hard to study.

According to theory, however, somewhere above element 110 , elements should become more "stable," perhaps so stable they could last for years. This domain is known as the "island of stability."

Elements 113 and 115 didn't live long; they decayed within seconds. Even so, like the shallow water that tells sailors they're approaching land, 113 and 115 hint that future physicists could create much longer-lived super heavies in particle accelerators.

Super-heavy elements offer one way for physicists to test the limits of theories of nuclear physics, just as architects implicitly test the limits of building materials by using them to build ever-bigger skyscrapers. Commercially, super heavies have no known uses.

The discovery of 113 and 115 is reported in Monday's issue of the nuclear physics journal Physical Review C, in an article written by 18 scientists at the Joint Institute for Nuclear Research at Dubna, Russia, and eight researchers at Lawrence Livermore, the nuclear weapons lab in Livermore.

Last summer, using a Russian particle accelerator called U400, the scientists fired a beam of atomic nuclei composed of the isotope calcium-48 at a target made of the isotope americium-243. The particle collisions generated at least four atoms of element 115. After each collision, 115 quickly decayed into element 113.

"The data is just all numbers," says a scientist on the U.S. team, Joshua Patin of Livermore. Although "fairly convinced" that they've discovered new elements, he said he would "feel much better" when another laboratory has achieved the same result.

Patin's remarks reflect a new caution in the tiny field following a scandal at Livermore's sister lab, Lawrence Berkeley National Laboratory.

In 2001, a distinguished LBNL scientist, Victor Ninov, was fired after investigators concluded he had faked the results of a 1999 experiment to find another super-heavy element known as 118. The investigators also complained that Ninov's colleagues had failed to double-check his work.

Since then, super-heavy researchers have peered more anxiously over each other's shoulders. After last summer's experiments, for example, researchers in Russia and Livermore simultaneously and independently analyzed the same collision data, as if they were rival teams of accountants called in to examine the suspicious business ledgers.

Due to "what happened at Berkeley," Patin says, "there's an enhanced awareness ... that you need to have not just one person do the data analysis."