Researchers are normally hard-pressed to catch a fleeting glimpse of the so-called superheavy elements at the far edge of the periodic table. Now a team has gone a step further and studied the chemistry of short-lived element 112, which seems to bond with other elements in the same way as its mundane relatives zinc and mercury.
"In principle, we are proving whether the good old basic systematics of chemistry—the periodic table—is a valid ordering principle also for transactinides," or superheavy elements, says chemist and team leader Robert Eichler of the Paul Scherrer Institute in Villigen, Switzerland, and the University of Bern.
Eichler and colleagues bombarded a plutonium 242 target with an intense beam of calcium 48 ions inside a vacuum chamber. Prior work indicated that the two atoms should now and then fuse into an isotope of element 114 (with 114 protons and 287 neutrons), which would rapidly decay into "ununbium," or element 112 (112 protons and 283 neutrons).
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In the new experiment, the bombardment ejected its products into the chamber, where a stream of helium gas ushered them to a chilled gold-coated detector that was warmer on one side than the other. The team also introduced the inert gas radon and the element mercury, which would lie in the same column as element 112 on the periodic table. Atoms of each element would stick to the detector at the point where its temperature was just low enough to let them form chemical bonds with gold.
Theorists had speculated that element 112's relatively charged nucleus might contract its electron cloud, making the atom largely unreactive, like radon.
So the researchers looked for signs of ununbium decay and compared their detector positions with those of the two other elements. They spotted a grand total of two telltale ununbium decays on the warmer, mercury-grabbing end of the detector. The decays also indicated a relatively long half-life of a few seconds, as expected.
Eichler says the experiment's main goal was to confirm reports that the bombardment process produced element 112, which is still not an official element. Getting a bead on its chemistry was a bonus. "We succeeded in both and this makes me as a chemist very happy," Eichler says. "There have been so many varying predictions about the chemical behavior [of] element 112. We wanted finally to know."
Researchers believe that certain "magic" numbers of protons and neutrons would confer high stability and long half-lives on element 114 and still undiscovered transactinides—a so-called island of stability in the upper reaches of the periodic table, which is generally inhabited by elements that exist only a fraction of a second.
"The observations of [element] 112 confirm that the island of stability is not just a mirage," wrote radiochemist Andreas Türler of Munich Technical University in an editorial accompanying the study in this week's Nature.