enews.lbl.gov/Science-Articles/Archive/elements-116-118.html
Department of Energy's Lawrence Berkeley National Laboratory. Element 118 and its immediate decay product, element 116, were discovered at Berkeley Lab's 88-Inch Cyclotron by bombarding targets of lead with an intense beam of high-energy krypton ions. Although both new elements almost instantly decay into other elements, the sequence of decay events is consistent with theories that have long predicted an "island of stability" for nuclei with approximately 114 protons and 184 neutrons. Said Ken Gregorich, a nuclear chemist who led the discovery team, "We were able to produce these superheavies using a reaction that, until a few months ago, we had not considered using. However, theoretician Robert Smolanczuk (a visiting Fulbright scholar from the Soltan Institute for Nuclear Studies in Poland) calculated that this reaction should have particularly favorable production rates. Walter Loveland, on sabbatical from Oregon State University, also made major contributions to this work. Other participants from the NSD included long-time leaders in the search for superheavy elements Albert Ghiorso and Darleane Hoffman, plus Diana Lee, Heino Nitsche, Wladyslaw Swiatecki, Uwe Kirbach, Carola Laue, and graduate students from the University of California at Berkeley Jeb Adams, Joshua Patin, Dawn Shaughnessy, Dan Strellis, and Philip Wilk. Hoffman and Nitsche are also professors of chemistry at UC Berkeley. Secretary of Energy Bill Richardson, whose department funded this work said, "This stunning discovery which opens the door to further insights into the structure of the atomic nucleus also underscores the value of foreign visitors and what the country would lose if there were a moratorium on foreign visitors at our national labs. By comparison, the heaviest element found in nature in sizeable quantities is uranium which, in its most common form, contains 92 protons and 146 neutrons. Transuranic elements in the periodic table can only be synthesized in nuclear reactors or particle accelerators. Though often short-lived, these artificial elements provide scientists with valuable insights into the structure of atomic nuclei and offer opportunities to study the chemical properties of the heaviest elements beyond uranium. Within less than a millisecond after its creation, the element 118 nucleus decays by emitting an alpha particle, leaving behind an isotope of element 116 with mass number 289, containing 116 protons and 173 neutrons. This daughter, element 116, is also radioactive, alpha-decaying to an isotope of element 114. The chain of successive alpha decays continues until at least element 106. Elements 118 and 116 were discovered by accelerating a beam of krypton-86 ions to an energy of 449 million electron volts and directing the beam into targets of lead-208. This yielded heavy compound nuclei at low excitation energies. During the last several years, low excitation energy reactions failed to take scientists beyond element 112, and it was assumed that production rates for heavier elements were too small to extend the periodic table further using this approach. However, the recent calculations of Smolanczuk indicating increased production rates for the Kr-86 + Pb-208 reaction prompted the experimental search for element 118 at Berkeley Lab. The key to the success of this experiment was the newly constructed Berkeley Gas-filled Separator (BGS). Said Gregorich, "The innovative BGS design has resulted in a separator with unsurpassed efficiency and background suppression which allows us to investigate nuclear reactions with production rates smaller than one atom per week. In operation since 1961, the 88-inch Cyclotron has been upgraded with the addition of a high-performance ion sources and can now accelerate beams of ions as light as hydrogen or as heavy as uranium. The 88-Inch Cyclotron is a national user facility serving researchers from around the world for basic and applied studies. Said I-Yang Lee, scientific director at the 88-Inch Cyclotron, "From the discovery of these two new superheavy elements, it is now clear that the island of stability can be reached. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California.
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