Dr. Nazarewicz is a theoretical physicist who lends his expertise to both the University of Tennessee and the Oak Ridge National Laboratory. His specialty is the nucleus, the bundle of neutrons and protons that serves as the nerve center of all atoms and contains most of their mass. When the Curies discovered 100 years ago that not all nuclei are stable (radioactivity), a new era began for science. Physicists began to wonder what were the limits of charge and mass for a nucleus. By playing with the numbers of protons and neutrons, they could synthesize elements in laboratories. But while naturally occurring elements are long-lived, the unstable lab-created variety had much shorter lifetimes, quickly falling victim to decay. Thus the challenge for theorists like Dr. Nazarewicz was to draw some sort of blueprint to map out the uncharted territory of the nuclear landscape (or "terra incognita," as he calls it) to create heavy elements, or, as he says, "see how far you can go in atomic mass; how heavy you can make the stuff." For the past several years, he and his colleagues from Warsaw and Brussels have been designing mathematical models to do just that. As it turns out, another group of physicists was conducting an experiment that would fit those blueprints quite well.
Dr. Nazarewicz's illustration of the nuclear landscape, which compares the region of unknown nuclei to unexplored territory in Africa (terra incognita).
A New Addition to the Periodic Table? Maybe.
During November and December of 1998, scientists from the Joint Institute for Nuclear Research in Russia and Lawrence Livermore Laboratory were busy running experiments to see just how "heavy" they could go. For 40 days, they bombarded plutonium targets with calcium ions, creating 1018 collisions. Of all those, one decay chain stood out as a candidate to be a new element, number 114. The chain had a much longer lifetime than the last element, 112, discovered in 1996. When Dr. Nazarewicz and his team heard of the project, they provided the experimentalists with their mathematical models and found remarkable agreement between the theory and experiment. In April of this year, another team from Lawrence Berkeley National Laboratory and Oregon State University performed similar experiments, using lead targets and krypton ions. The results showed three decay chains, indicating not only element 114 but elements 116 and 118 as well. Robert Smolanczuk of Poland's Soltan Institute provided the initial theory calculations for this work, which was also supported by the calculations by S. Cwiok (Warsaw/JIHIR), Dr. Nazarewicz, and P.H. Heenen (Brussels/JIHIR).
Although he is quick to acknowledge the data are not 100 percent conclusive, Dr. Nazarewicz is certainly encouraged by the evidence his work provides for the possible existence of element 114. These are "calculations that greatly support the identification made in experimental papers," he said. The work is being chronicled in the scientific literature, as the experimental group submitted a paper in March 1999 to Physical Review Letters, to be followed by another paper by Dr. Nazarewicz's theory group. A second experimental paper, on a second isotope of element 114, has also been submitted to Nature by the Dubna group. The Berkeley/Oregon paper was submitted to the same journal in June 1999. Below is what the periodic table looks like with the possible inclusion of elements 114, 116, and 118.
Gaining Ground on the "Magic Nuclei"
Dr. Nazarewicz explained that what makes this work so exciting is that it demonstrates that scientists are getting closer to the superheavy "magic nuclei," longest-lived super-heavy elements. Scientists began making predictions about these elements some 30 years ago. In 1981, Bohrium (element 107) became the first member of the superheavy class. Since then, Dr. Nazarewicz explained that subsequent element discoveries are "slowly approaching greater shell stability," as their lifetimes have gone from microseconds to several minutes. As explained in the 1999 National Research Council report, Nuclear Physics: the Core of Matter, the Fuel of Stars, "superheavies" are important because they would provide "crucial information on relativistic effects in atomic physic and quantum chemistry."
The superheavies represent the fourth period of radioactive element discovery in scientific history. The first (1896-1940) was characterized by the Curies' work and the discovery of polonium. The Manhattan Project marked the second period (1940-1952), when plutonium became part of the periodic table. The third period (1955-1974) witnessed a Cold War competition of sorts between Russian laboratories at Dubna and American laboratories in Berkeley to discover new elements. The fourth period (1974-1996) has been dominated by work in Darmstadt, Germany, which has been responsible for six new elements since 1981. The last three (110, 111, and 112) are still unnamed, due to the "politics involved," Dr. Nazarewicz said. Because of disputes over the proper name for these new elements, the International Union for Pure and Applied Chemistry has devised a Latin system to give each a temporary name based on its individual numbers. So for now, 114 is technically ununquadium, 116 is ununhexium, and 118 is ununoctium.
Although more experimentation will be necessary to prove the elements' existence, Dr. Nazarewicz will turn his attention back to drawing new blueprints of the nuclear landscape in search of magic nuclei.
"I'm a theorist," he says with a laugh. "I don't smash atoms."