Page 2 of 2   <      

Scientists Announce Creation of Atomic Element, the Heaviest Yet

Calcium ions travel through an accelerator toward a rotating target of californium in this illustration.
Calcium ions travel through an accelerator toward a rotating target of californium in this illustration. (By Sabrina Fletcher And Thomas Tegge -- Lawrence Livermore National Laboratory)

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.


<       2

© 2006 The Washington Post Company