Russian and US scientists say they have produced a new super-heavy atom - albeit for just fractions of a second.
Schematic impression: It has the temporary name ununoctium
The element has 118 protons in its nucleus, an arrangement never before seen in nature or in the laboratory.
Three of the atoms were detected when calcium was smashed into a target made from californium; they then rapidly decayed into lighter elements.
The scientists report their work in the journal Physical Review C.
They are based at the Lawrence Livermore National Laboratory, in California; and the Joint Institute for Nuclear Research (JINR) at Dubna, north of Moscow.
Element 118 is expected to be a noble gas that lies right below radon on the periodic table of elements.
"The world is made up of about 90 elements," said Ken Moody, Livermore's team leader. "Anything more you can learn about the periodic table is exciting. It can tell us why the world is here and what it is made of."
Atoms consist of a central nucleus surrounded by a cloud of electrons. The nucleus is made up of protons and neutrons.
But not all combinations of protons and neutrons are stable. In nature, no element heavier than uranium, with 92 protons and 146 neutrons, can normally be found.
To make super-heavy elements like 118, scientists will collide two large nuclei together in the hope that they will form a new, heavier nucleus. Theory predicts that there is an "island of stability" for certain large combinations of protons and neutrons, and that these super-heavy isotopes, or types of atom, will hold together for a period of milliseconds.
The current research supports this theory.
The researchers saw the element 118 atoms last only 0.9 milliseconds. They decayed to element 116 and then to element 114.
The researchers said the work encouraged them to go for even bigger atomic numbers than 118.
"The heavy element community will continue to search for new elements until the limit of nuclear stability is found," Lawrence Livermore scientist Mark Stoyer said. "It is expected that limit will be found."
In 2007, the Livermore-Dubna team plans to look for element 120 by bombarding a plutonium target with iron.
The 118 element has the temporary name ununoctium.
Researchers at Lawrence Berkeley National Laboratory in the US reported the element's discovery in 1999 but then retracted the claim when other labs could not reproduce their results. It was then established that one of the scientists involved had used faked data.