BERKELEY, Calif. - Nuclear chemists from Oregon State University and the Lawrence Berkeley National Laboratory today announced the discovery of two new "superheavy" elements and successful use of a technique that may open the door to further breakthroughs in chemistry and physics.
The newest additions to the periodic table are elements 118 and its immediate decay product, element 116, created by bombarding targets of lead with an intense beam of high-energy krypton ions.
The success in producing these superheavy elements with the Berkeley lab's 88-inch cyclotron "opens up a whole world of possibilities using similar reactions - new elements and isotopes, tests of nuclear stability and mass models, and a new understanding of nuclear reactions for the production of heavy elements," said Ken Gregorich, a nuclear chemist with the Lawrence Berkeley National Laboratory, who led the discovery team.
Walter Loveland, an OSU professor of chemistry and expert in nuclear heavy ion reactions, was part of the project. He said that the cold fusion reaction mechanism used in this discovery "may well be able to synthesize other new elements in coming months or years."
"We didn't expect this to work, but we gave it a try and it paid off spectacularly well," Loveland said. "This is a giant leap ahead, because prior to this it has been considered extremely difficult to create new elements above 112 using cold fusion technologies.
"And anytime you discover two new chemical elements it's exciting, because these are the building blocks of nature," Loveland said.
Building upon this discovery, Loveland said the research may use similar approaches to discover elements 113, 115, 117, and 119; perhaps find longer-lived isotopes; and ultimately further expand the frontiers of chemistry and physics.
The discovery of element 114 was announced by a different research group earlier this year, Loveland said, but sometimes five to 10 years goes by between fundamental advances such as this.
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.
"We jumped over a sea of instability onto an island of stability that theories have been predicting since the 1970s," said nuclear physicist Victor Ninov, who was first author of a paper that has been submitted to Physical Review Letters.
Noting that four members of the discovery team are German citizens, U.S. 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. Scientific excellence doesn't recognize national boundaries, and we will damage our ability to perform world-class science if we cut off our laboratories from the rest of the world."
The newly identified isotope of element 118 with mass number 293 contains 118 protons and 175 neutrons in its nucleus. 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.
The key to the success of this experiment was the newly constructed Berkeley Gas-filled Separator, researchers said. Another important factor for the experiment's success was the unique ability of the 88-inch cyclotron to accelerate neutron-rich isotopes such as krypton-86 to high-energy and high-intensity beams with an average current of approximately 2 trillion ions per second.
From the discovery of these two new superheavy elements, it is now clear that the "island of stability," can be reached, scientists said. Additionally, similar reactions can be used to produce other elements and isotopes, providing a rich new region for the study of nuclear and even chemical properties.
Loveland, an expert in nuclear heavy ion reactions at low, intermediate, relativistic and ultrarelativistic energies, received his doctorate in chemistry from the University of Washington in 1965 and has been on the OSU faculty since 1967. In the past he did extensive research with the late Nobel laureate Glenn Seaborg.