Nuclear Scientists Eye Future Landfall on a Second “Island of Stability”

Newswise — Modern-day scientific Magellans and Columbus's, exploring the uncharted seas at the fringes of the Periodic Table of the Elements, have landed on one long-sought island — the fabled Island of Stability, home of a new genre of superheavy chemical elements sought for more than three decades.

In a presentation at the 235th national meeting of the American Chemical Society, one of the captains of these expeditions into the unknown, described how researchers now are eying other islands on the more-distant fringes of the periodic table. "Now that it has been shown that the 'island of stability' of superheavy elements exists, it would be interesting to predict the position of other islands," said Yuri Oganessian, Ph.D., of Russia's Joint Institute for Nuclear Research in Dubna. He is the scientific leader at the Institute's Flerov Laboratory of Nuclear Reactions.

The discovery of superheavy elements at the beginning of this century by Oganessian's group also confirmed the existence of the Island of Stability, a theoretical region of the periodic table, which distinguished chemist and Nobel laureate Glenn Seaborg considered as one of the keystones of fundamental science. The "sea-and-island" analogy arose because these superheavy elements lie in an area of the periodic table where other elements are unstable, disappearing in much less than the blink of an eye. The superheavies, in contrast, are somewhat more stable than their shorter-lived cousins.

Oganessian's group has teamed with California's Lawrence Livermore Laboratory to synthesize five new elements (113, 114, 115, 116, and 118) over the past six years. Such superheavy elements do not exist in nature and can only be created by smashing lighter elements together at tremendous speeds obtained by means of highly sophisticated particle accelerators.

The periodic table, a fixture on the walls of science classrooms around the world, lists all the chemical elements. These materials make up everything in the universe, from human beings, medicines, and food to stars and swirling clouds of gas a billion light-years across the universe. Click here to view the ACS's interactive Periodic Table of the Elements.

The first 92 elements on the table exist naturally. The rest " which now extend to element 118 " were created by scientists in atomic nuclei collision with the aid of particle accelerators. Aptly named, these machines accelerate atoms to nearly 1/10 the speed of light and smash them into other so-called "target" atoms. Sometimes the nuclei of two colliding atoms fuse and a new element is formed.

Oganessian and his colleagues are currently using Dubna's particle accelerator in an attempt to synthesize yet another superheavy element, No. 120, to add more territory to the island of stability. Strikingly, Oganessian believes that another, more distant, island of stability lies further out in that sea at the periodic table's fringes.

"The next island is located very far from the first one," said Oganessian. How far away might that next island be? In terms of numbers on the periodic table, it could lie around atomic number 164, as some theorists predicted, certainly a long way from where researchers are exploring today in hopes of discovering element 120.

But reaching the shores of the next island of stability will require a more deep understanding of the processes of element formation and a newer, more sophisticated particle accelerator, Oganessian believes.

In order to study the physical and chemical properties of the current and yet-to-be discovered superheavy elements, the researchers will need to produce many more nuclides than they have been able to do so far, according to Oganessian.

"For this purpose, we need to increase the beam intensity, which will demand a new accelerator," Oganessian said.

It is difficult to anticipate what practical uses might come out of the search for new superheavy elements. For now, the focus is on discovery, not application. However, some previously synthesized elements have yielded tremendous benefits for people. One example, element 95 " Americium " discovered in 1944, is used in smoke detectors and in medical and industrial radiography.

Oganessian declined to speculate on potential uses of future superheavy elements, but noted that it will take revolutionary new technology to produce large enough amounts of these elements to make them of practical use. Although he said it is hard for him to imagine such a technology, he expressed faith in the abilities of future researchers.

"I don't want to fantasize, but if they can devise a method for the production ofsuperheavy elements in large quantities, I am sure they can find some worthy application for these elements," Oganessian said.

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The paper on this research, NUCL 007, will be presented at 8:40 a.m., Sunday, April 6, at the Morial Convention Center, Room 253, during the symposium, "Developments in Advanced Characterization Techniques in Actinide and Transactinide Science."

Yuri Oganessian, Ph.D., is with the Joint Institute for Nuclear Research in the Dubna, Moscow, region in Russia. ALL PAPERS ARE EMBARGOED UNTIL DATE AND TIME OF PRESENTATION, UNLESS OTHERWISE NOTED

NUCL 007Plenary Lecture. Superheavy elements Program Selection: Division of Nuclear Chemistry & TechnologyTopic Selection: Developments in Advanced Characterization Techniques in Actinide and Transactinide Science: Perspectives on TransactinidesLead Presenter's Email:

Yu. Ts. Oganessian, Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, 141980 Dubna, Moscow region, Russia, Fax: 7 49621 6 5083,

Abstract

The existence of transactinides is determined by the structure of the heaviest nuclei. Nuclear stability increases in the vicinity of closed proton and neutron shells. The nuclear shell model predicts stability islands in the domain of superheavy elements. Enhanced stability is expected for deformed nuclei near Z=108 and N=162, yet stronger effects are predicted for spherical nuclei close to Z=114 and N=184. This lecture is devoted to experimental verification of these predictions. Fusion reactions of 208Pb, 209Bi with 50Ti, 54Cr, 70Zn, etc. projectiles (cold fusion) produce nuclides with Z=104-113, N=151-165 in the region of deformed shells (Z=108, N=162). These nuclides undergo sequential alpha-decays to known transactinides. The synthesis of heavier, neutron-rich nuclei is carried out in reactions of 233,238U, 237Np, 242,244Pu, 245,248Cm and 249Cf with 48Ca projectiles (hot fusion), creating nuclides with Z=104-118 and N=161-177. These experiments show that adding six neutrons to isotopes with Z=110-114 results in an increased stability (about five orders of magnitude) as an effect of the spherical shell N=184. The nuclides undergo sequential alpha-decays ending in spontaneous fission of long-lived isotopes of Rf and Db. Energies and half-lives have been measured for 34 nuclei and are compared with theoretical calculations from various models. This lecture presents experiments on the detection of superheavy nuclides with in-flight recoil separators. Off-line liquid phase extraction of 268Db, the final product in the decay of (288)115, and the study of elements 112 and 114 by absorption gas chromatography will be discussed. The search for superheavy elements in nature and cosmic rays, as well as the search for spontaneous fission of Hs (Z=108) and its daughters under way underground in Modane (France), will be described. Results are from FLNR (Dubna, Russia) in collaboration with LLNL (Livermore, USA) and PSI (Villigen, Switzerland), GSI (Darmstadt, Germany), RIKEN (Wako-shi, Japan) and LBNL (Berkeley, USA). ________________________________________

Researcher Provided Non-Technical Summary Briefly explain in lay language what you have done, why it is significant and what are its implications (particularly to the general public)

Our research is related to the attempt to define the limits of existence of the material world as atoms and chemical elements. The synthesis of the hypothetical elements gives a possibility to check many of our conceptions, which have been obtained for lighter atoms, in the far unexplored region of superheavy nuclides. At this place, according to some theoretical predictions the world of atoms ends, whereas on the opposite others predict the islands of stability of new elements. Now for the first time it is experimentally established that appearance of the hypothetical atomic giants exist in reality.

The stability of superheavy elements strongly depends on the structure of the atomic nucleus, while the chemical properties may differ from those of their light homologs. There are serious reasons to believe that the superheavy nuclei were "born" at the early stages of forming of the Solar system and in the explosions of supernovas in other galaxies (cosmic rays).

For this reason the existence of islands of stability in the region of superheavy elements, their nuclear and chemical properties are of fundamental importance for nuclear physics (for the structure of the nuclei, the dynamics of collective motion in nuclei, nuclear reactions and nuclear fission modes), also for chemistry (test of the fundamental law of the periodical properties of chemical elements), for astrophysics (the formation of heavy nuclei in the process of nucleosynthesis), etc.

Because of the micro-quantities of production (single atoms), superheavy elements can not have a direct application in new technologies now.

How new is this work and how does it differ from that of others who may be doing similar research?

The work on the synthesis of the 6 heaviest elements from 112 to 116 (except 117) has lasted for the last 6 years. It was preceded by a 4-year technical preparation period, in which a significant increase of the experimental sensitivity was achieved. For the synthesis of superheavy nuclei we used the fusion reaction of the rare isotope " calcium-48 with uranium and transuranium nuclei: plutonium, americium, curium and californium, which are produced in high-flux reactors. Earlier, all elements lighter than element 112 were obtained in other reactions, whereas lead and bismuth targets were used. But these reactions cannot bring us to the "islands of stability" of superheavy elements.