A new theory explains some of the unusual properties of plutonium, the radioactive metal best
known for its proclivity to undergo nuclear fission chain reactions,
making it a potent fuel for nuclear weapons and power plants.
Plutonium is one of the most unusual metals--it's not magnetic and
it does not conduct electricity well. The material also changes its
size dramatically with even the slightest changes in its temperature
and pressure. The atom's unusual set of properties distinguishes it
from even its closest neighbors on the periodic table, such as americium.
What makes plutonium unique? In the new theory,
developed by condensed-matter theorists at Rutgers University in New
Jersey, plutonium's eight outermost or "valence"; electrons can
circulate among different orbitals, or regions around the atom. In
plutonium's 5f orbital, the one with the greatest influence on its
atomic properties, the number of valence electrons it contains is
most often five (approximately 80% of the time), but can also be six
(about 20% of the time) or four (less than 1% of the time),
according to the theory. These electrons shuttle in and out of the
5f orbital very quickly--on the order of femtoseconds, or
quadrillionths of a second, the researchers say.
Plutonium is an example of a strongly correlated material, in which the valence
electrons interact with each other to a great degree, and cannot be
treated as independent agents. Taking these interactions into
account, the researchers combined two theoretical approaches to
solid materials, called the local density approximation and
dynamical mean field theory, to come up with their sophisticated
As their analysis shows, the 5f orbital dictates many of
plutonium's key properties, such as its lack of conductivity and net
magnetism. With their theory, the researchers have also explained
the magnetic and electrical properties of americium and curium.
They hope their approach will also elucidate the properties of
rare-earth elements on the periodic table (Shim et al., Nature, 28