Element 118 Created, This Time for Real, Scientists Say
Richard A. Lovett
for National Geographic News
|October 20, 2006|
A team of Russian and American physicists says it has created three atoms of a new element.
The as-yet-unnamed element, element 118, is the heaviest yet discovered, with a nucleus consisting of 118 protons and 176 neutrons.
The heaviest naturally occurring element is uranium, which has 92 protons. Its most common form, or isotope, has 146 neutrons. Scientists have also artificially created most of the other elements between uranium and element 118. (Related: "Nuclear Tech Not a 'New Capability' for North Korea, Experts Say" [October 13, 2006.)
The newest element was created in a particle accelerator in Dubna, Russia, that shot a beam of calcium-48 ions (containing 20 protons) into a target of californium 249, an artificial element with 98 protons (map of Russia).
To create a mere three atoms of element 118, the scientists spent two months bombarding the californium target with 30 billion billion calcium ions.
"Most of them just go right through the target and don't do anything," said Mark Stoyer, a nuclear chemist at Lawrence Livermore National Laboratory who was part of the research team.
Only rare head-on collisions occurring with just the right energy caused the two elements to stick together to form a new super-heavy atom, Stoyer said. "One of the reasons we did it in Dubna is because they have a very intense beam of calcium 48."
A detector allowed the researchers to track radiation and by-products created by the high-energy collisions.
By working backward through a decay sequence, the scientists are reasonably certain they created element 118, even though the highly unstable new atoms survived only a millisecond apiece.
Element 118 first decayed into element 116, then into element 114. That decayed into element 112, which split into two roughly equal pieces, the researchers say.
Their next goal is to create element 120 by beaming iron atoms (26 protons) at a plutonium target (which has 94 protons).
No Sure Thing
The new finding will appear in the October issue of the journal Physical Review C. But it isn't time to officially add the new element to the periodic table quite yet.
Before that can happen, the discovery needs to be confirmed. It's particularly important in this case because research into element 118 has a checkered history.
In 1999 a team from Lawrence Berkeley National Laboratory, in Berkeley, California, announced that it had created element 118, only to retract the claim when it was discovered that one of the scientists had faked some data.
"Because of the previous history on this subject, one has to be very cautious in drawing conclusions until the result is confirmed," said George Bertsch, a physicist at the University of Washington in Seattle who was not involved in the experiment.
Stoyer agrees. "We saw something interesting, and the way we've interpreted it, it's element 118," he said. "But you need someone else to duplicate it. A fundamental tenet of science is reproducibility."
But it might be a while before the experiment is repeated. "You're working with californium 249, which is fairly radioactive," Stoyer said. "Not many labs in the world either want to work with it or have the capabilities to work with it."
Island of Stability?
Element 118 and most other elements heavier than uranium are highly unstable, decaying far too quickly for scientists to study how they behave.
So researchers are seeking a theoretical "island of stability"—a group of super-heavy elements that might hang around long enough to allow their properties to be looked at in detail.
One island of stability exists for uranium and thorium, which persist in nature for long periods of time even though their neighbors on the periodic table decay very quickly.
Nobody is quite sure, however, what precise combination of protons and neutrons are needed for the next island of stability.
Stoyer thinks that it might require 120 to 126 protons and about 184 neutrons.
But Bertsch, of the University of Washington, thinks that the new discovery, if confirmed, may show that scientists have already overshot the ideal number of protons.
"The interesting thing is that one is seeing the [element] lifetimes go down as one is making [elements] heavier by adding protons," he said.
Unfortunately, he added, "the island requires many more neutrons than one is able to do with these experiments. So one can't actually see it if one is just skirting by the edge."
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