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New Element Isolated Only Briefly
Wednesday, October 18, 2006
Scientists at Lawrence Livermore National Laboratory announced the discovery of element 118 Monday after years of working on isolating the element for at least a blink of a second.
The Livermore lab researchers teamed up with scientists at the Joint Institute for Nuclear Research in Dubna, Russia, to successfully isolate three atoms of the new element for a fraction of a second.
Element 118, which contains 118 protons, is the heaviest element discovered so far. It is predicted to fall below radon on the periodic table and is considered part of the noble gases.
The scientists used a particle accelerator to speed up calcium ions and bombard the element californium.
Scientists chose to use an isotope of calcium and californium because they are neutron-rich elements and when combined, they produce the necessary number of protons and neutrons to make element 118, said Philip Wilk, a member of the Livermore team.
The reaction products from the collisions were placed in a large magnetic separator. The separator has a detector that has been set to detect element 118, also referred to as “eka-radon.”
“Some very, very small percentage of the time when you throw billions of billions of calcium ions at this target, some small tiny percentage of the time you get the total fusion together to create element 118,” Wilk said. “Most of the time you just get a bunch of stuff.”
Since the separator works by filtering the reaction products based on similar mass charges, the scientists can instruct the detector to look for a particular mass based on the expected number of protons and neutrons.
In addition, the detector measures tiny bursts of energy during the decay of the element. Therefore, the scientists can track a series of decays, ending with the final spontaneous fission.
“Using a lot of experience we had on elements like 116, 114 and 113, we can make a pretty darn good estimate to maximize our chances of finding it,” Wilk said.
The discovery of eka-radon gives further support to the idea of “island of stability.” The concept, proposed by late UC Berkeley professor and former chancellor Glenn Seaborg, explains why superheavy elements such as element 118 last longer than predicted.
The stability of an element is determined based on its outermost electron shell. If the shell is completely filled with electrons, then it is considered stable and thus does not easily react with other elements.
According to Seaborg’s theory, the concept of orbitals also applies inside the nucleus, and like electrons, nuclei have shells. When filled, the element is more stable.
Although eka-radon does not exist in nature, it may be possible one day to synthesize the element in a lab and use it for further study.
“It gives us a lot of fundamental knowledge to understand the periodic table,” Wilk said.
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