International team fills gap in the periodic table
Editor’s Note: Additional material was added to this story at 5 p.m. on April 6, 2010.
Physicists have reported synthesizing element 117, the latest achievement in their quest to create “superheavy” elements in the laboratory. A paper describing the discovery has been accepted for publication in Physical Review Letters.
A team led by Yuri Oganessian of the Joint Institute for Nuclear Research in Dubna, Russia, reports smashing together calcium-48 — an isotope with 20 protons and 28 neutrons — and berkelium-249, which has 97 protons and 152 neutrons. The collisions spit out either three or four neutrons, creating two different isotopes of an element with 117 protons.
Sigurd Hofmann, a nuclear physicist at the GSI research center in Darmstadt, Germany, calls the new work on element 117 “convincing.”
Most elements heavier than uranium, which has 92 protons, do not exist stably in nature and must be made artificially in the laboratory.
The Russians collaborated with U.S. researchers, including from Vanderbilt University and Oak Ridge National Laboratory in Tennessee, where the berkelium target was made. Berkelium, with atomic number 97, is another of the rare artificially produced elements; the Russian team was able to obtain just 22 milligrams of it from Oak Ridge.
The researchers briefly spotted signs of element 117 during two runs of collisions lasting 70 days each. In their paper, the researchers report observing the heavier isotope of element 117 decay with a half-life of 78 milliseconds; they measured the lighter one’s half-life at 14 milliseconds.
The new element, which has yet to be named, slips into a place on the periodic table between elements 116 and 118, both of which have already been discovered. Such superheavy elements are usually very radioactive and decay away almost instantly. But many researchers think it is possible that even heavier elements may occupy an “island of stability” in which superheavy atoms stick around for a while.
The new work supports that view. Analyses of the new element’s radioactive decay, Oganessian’s team writes in the new paper, “represent an experimental verification for the existence of the predicted ‘Island of Stability’ for super-heavy elements.”
Hofmann says that one of the most interesting things about the new work is the different products that result when the two element 117 isotopes decay. The isotope with 177 neutrons decays down to dubnium (atomic number 105), whereas the isotope with 176 neutrons decays down to roentgenium (atomic number 111). Comparing the two chains, Hofmann says, will help researchers better understand the characteristics of superheavy elements.
Element 117 is tentatively known as ununseptium. After its existence is confirmed, it will receive a permanent name, suggested by the discoverers, from the International Union of Pure and Applied Chemistry – a process that can take some time. In February 2010, the IUPAC finally granted the name copernicium to element 112, which was first produced by Hofmann’s group in 1996.
Yu. Ts. Oganessian et al. 2010. Synthesis of a new element with atomic number Z=117. Phys. Rev. Lett. 104, April 9, 2010, 142502.