Source: Rutgers
Date: March 29, 2007
More on:

Scientists Unlock Physical, Chemical Secrets Of Plutonium

Science Daily Researchers at Rutgers, The State University of New Jersey, have unlocked some of the physical and chemical secrets of plutonium, an element known for its use in atomic weapons and power plant fuel. While the complex nuclear characteristics of plutonium are well-known, it has properties as a metal or a chemical compound that have often left scientists scratching their heads.

Writing in this week's issue of Nature, a prestigious international scientific journal, Rutgers physicists report that the valence electrons -- those which control how atoms bond with each other -- fluctuate among different orbitals in solid plutonium metal on a very short time scale. In contrast, earlier theories specified fixed numbers of valence electrons in those orbitals. The Rutgers findings help explain some contrary characteristics of plutonium: Unlike many metals, plutonium is not magnetic and not a good conductor of electricity, and it shows greater changes in volume under small changes in temperature and pressure.

While the authors' findings and study methods are mainly of interest to other researchers seeking clear explanations of complex materials, the knowledge may someday help scientists create safer and more versatile nuclear materials for energy, industry and medicine.

"Previous theories about plutonium's makeup placed a fixed number of valence electrons in the particular orbital we examined, known as the 5f orbital," said Kristjan Haule, an assistant professor of physics and astronomy at Rutgers. "Different theories assigned different numbers of electrons to that orbital -- some four, others five and yet others, six. But whatever number the theory prescribed, it remained constant. Each theory could explain some of the element's characteristics, but none could account for all the experimental evidence."

The Rutgers approach abandoned the idea of a fixed or unique number of valence electrons in the 5f orbital. "We revisited the notion of valence in a solid," Haule said. "While it happens rarely in nature, we thought it should be possible for the number of valence electrons to fluctuate among orbitals in atoms that are part of a solid structure."

It turns out that plutonium is especially suited to exhibiting this behavior. The Rutgers physicists determined that almost 80 percent of the time, there are five electrons in the 5f orbital. Almost 20 percent of the time, there are six, and less than 1 percent of the time, there are four.

"A theory that permits fluctuating valence electrons consistently explains properties that scientists observe in laboratory experiments," Haule said, citing recent results using X-ray absorption and electron energy-loss spectroscopy. "In addition, the theory accurately predicts the properties of two neighboring elements, americium and curium, which have similar atomic structures but show greatly differing magnetic and electric properties."

The new approach involves a merger of two existing theories, known as local density approximation and dynamical mean field theory, or LDA+DMFT. Taken separately, they and others fell short in accounting for all of plutonium's observed physical characteristics.

The work done by Haule and his colleagues is in a branch of physics known as condensed matter physics, which deals with the physical properties of solid and liquid matter. In particular, their work focuses on strongly correlated materials, which have strongly interacting electrons and, therefore, can't be described using theories that treat electrons as largely independent entities. The radioactive metals, such as plutonium, and their periodic table neighbors, known as rare earth elements, are examples of strongly correlated materials, with highly localized electrons in their f orbitals. In these elements, most of the physical properties such as electrical resistivity and magnetic characteristics depend on the f-orbital electrons. The findings reported in Nature strengthen methods for predicting characteristics of all of these complex materials.

Collaborating with Haule were Ji-Hoon Shim, a postdoctoral fellow, and Gabriel Kotliar, Board of Governors Professor of Physics.

The Division of Basic Energy Science of the U. S. Department of Energy and the Rutgers Center for Materials Theory supported their research. Shim received postdoctoral research funding from the Korean Research Foundation.

Note: This story has been adapted from a news release issued by Rutgers.


New! Search Science Daily or the entire web with Google:


Science Video News

Investigators on a crime scene can now use a new tool for collecting chemical or biological samples. The sampler gun collects samples on a cotton pad ... > watch video
Two mathematicians at the University of Northern Colorado are taking a fresh statistical look at the effects of elevation on hitting -- specifically ... > watch video
A new computer-based system gives physical therapists real-time, objective measures of the motion of each joint in the patient's body. The system ... > watch video
New studies by radiologists have shown that MRI can be just as accurate as CT scans at helping radiologists diagnose pathologies such as cancer, ... > watch video
Industrial toxicologists at a non-profit venture founded by Procter & Gamble developed PUR, a water purifier that combines a flocculant -- which ... > watch video
Psychologists are finding out that even when people try to focus on a task they tend to lose concentration within 40 minutes, and sometimes as little ... > watch video
Ordinary invasive fingerprinting techniques, such as dusting, are prone to damaging evidence. Micro-X-ray fluorescence images fingerprints without ... > watch video
America's only dog that's trained to sniff mercury is able to detect as little as a half-gram, and is faster and cheaper than traditional lab ... > watch video
Food scientists have discovered why Rice Krispies make their characteristic sound when soaked in milk. Rice Krispies contain lots of sugar and are ... > watch video
Ecological engineers have developed software that can model the path of a toxic spill in waterways anywhere in the United States. The system can ... > watch video
Computers could one day help football coaches make strategic decisions, such as going for the touchdown or for the kick, or accept the penalty or ... > watch video
Chemical engineers have developed a sensor that can almost instantly detect the presence of E. coli. The sensor is a millimeter-sized cantilever ... > watch video

Jump to: < prev | next >

Text: small | med | large
Find a Job
Job category:
> more

In Other News ...

... more breaking news at NewsDaily -- updated every 15 minutes

Health & Medicine Mind & Brain Plants & Animals Space & Time Earth & Climate Matter & Energy Computers & Math Fossils & Ruins