Uut and Uup Add Their Atomic Mass to Periodic Table
February 1, 2004
By JAMES GLANZ
A team of Russian and American scientists are reporting
today that they have created two new chemical elements,
called superheavies because of their enormous atomic mass.
The discoveries fill a gap at the furthest edge of the
periodic table and hint strongly at a weird landscape of
undiscovered elements beyond.
The team, made up of scientists from Lawrence Livermore
National Laboratory in California and the Joint Institute
for Nuclear Research in Dubna, Russia, is disclosing its
findings in a paper being published today in Physical
Review C, a leading chemistry journal. The paper was
reviewed by scientific peers outside the research group
"Two new elements have been produced," said Dr. Walt
Loveland, a nuclear chemist at Oregon State University who
is familiar with the research. "It's just incredibly
exciting. It seems to open up the possibility of
synthesizing more elements beyond this."
The periodic table is the oddly shaped checkerboard - with
an H for hydrogen, the lightest element, in the
upper-left-hand corner - that hangs in chemistry classrooms
the world over. Each element has a different number of
protons, particles with a positive electrical charge, in
the dense central kernel called the nucleus.
The number of protons, beginning with one for hydrogen,
fixes an element's place in the periodic table and does
much to determine an element's chemical properties: ductile
and metallic at room temperature for gold (No. 79), gaseous
and largely inert for neon (10), liquid and toxic for
Elements as heavy as uranium, No. 92 on the list, are found
in nature, and others have been created artificially. But
much heavier elements have been difficult to make, partly
because they became increasingly unstable and short-lived.
Still, for roughly half a century, nuclear scientists have
been searching for an elusive "island of stability,"
somewhere among the superheavies, in which long-lived
elements with new chemical properties might exist. Dr.
Loveland said that the new results indicated that
scientists might be closing in on that island.
"We're sort of in the shoals of the island of stability,"
said Dr. Kenton J. Moody, a Livermore nuclear physicist who
was one of the experimenters in the work.
"It's an amazing effect," he added. "We're really just
chipping away at the edges of it."
The experiments took place at a cyclotron, a circular
particle accelerator, in Dubna, where the scientists fired
a rare isotope of calcium at americium, an element used in
applications as varied as nuclear weapons research and
household smoke detectors. Four times during a month of
24-hour-a-day bombardment in July and August, scientists on
the experiment said, a calcium nucleus fused with an
americium nucleus and created a new element.
Each calcium nucleus contains 20 protons and americium 95.
Since the number of protons determines where an element
goes in the periodic table, simple addition shows the new
element to bear the atomic number 115, which had never been
seen before. Within a fraction of a second, the four atoms
of Element 115 decayed radioactively to an element with 113
protons. That element had never been seen, either. The
atoms of 113 lasted for as long as 1.2 seconds before
decaying radioactively to known elements.
Scientists generally do not give permanent names to
elements and write them into textbooks until the
discoveries have been confirmed by another laboratory. By
an international convention based on the numbers, element
113 will be given the temporary name Ununtrium (abbreviated
Uut for the periodic table) and element 115 will be
designated Ununpentium (Uup).
Dr. Loveland said he agreed that the new elements would
require independent confirmation before they could receive
final acceptance. And he conceded that the Dubna find was
likely to receive more than the usual amount of scrutiny:
two years ago, the reported discovery of Element 118 was
retracted after a scientist at Lawrence Berkeley National
Laboratory was found to have fabricated evidence.
The only other truly simultaneous discovery of two elements
in recent times came in 1952, when einsteinium (99) and
fermium (100) were discovered in the fallout from the
hydrogen bomb explosion at Eniwetok Atoll in the Pacific
Ocean. The most recent successful discovery of an element -
one that has received a name - came in 1994. That element,
No. 110, is called Darmstadtium for the city in
where it was discovered.
But as scientists wait for confirmation on elements 115 and
113, the data presented by the Dubna and Livermore groups
appear solid, said Dr. Sigurd Hofmann, a nuclear physicist
at the Institute for Heavy Ion Research in Darmstadt, the
laboratory where Darmstadtium was found.
"These Dubna data look quite convincing," Dr. Hofmann said.
"And I'm sure with some more experiments, it will finally
Dr. Joshua B. Patin, a 28-year-old nuclear chemist who is
the lead American author on the paper, said he had found it
deeply moving to add two more entries to a scientific icon
that dates to the 1860's. That was when the Russian chemist
Dmitri Ivanovich Mendeleyev noted clear patterns in the
chemical properties of the known elements and arranged them
into the periodic table, leaving gaps for other elements
that he correctly predicted would someday turn up.
"This is a working piece of art," Dr. Patin said. "We're
not done yet. Nothing's been finished. What it could really
mean down the road, nobody can tell. And that's the part
that's exciting to me."
The lead authorship on the work went to Dr. Yuri
Oganessian, scientific director of the Flerov Laboratory of
Nuclear Reactions at the Joint Institute for Nuclear
Research in Dubna, whose theoretical research in the 1970's
revealed the path that eventually led to the most recent
The experimental group that Dr. Oganessian leads is
especially skilled at using extremely small amounts of the
rare calcium isotope in the bombardment and at filtering
out signals from just a handful of new atoms among the
debris spewing from the collisions.
"These elemental discoveries underscore both the value of
federally supported basic research and the benefit of
unfettered international scientific collaboration," said
Energy Secretary Spencer Abraham, whose agency helped
finance the work.
In a written response to questions, Dr. Oganessian said the
results "favor the conclusion about the formation of a new
element and refute any other interpretation." He added that
confirmation of the work was necessary, but that everything
had been done to ensure that the analysis was correct.
"In order to exclude the human factor," Dr. Oganessian
said, "the analysis of the data is carried out in parallel
and independently by the two groups in Dubna and in
Physicists long ago discovered that atomic nuclei have what
came to be known as "magic numbers." Nuclei that contain
just those numbers of protons and their electrically
neutral cousins, neutrons, are especially stable. The
numbers 2, 8, 20, 28, 50, 82 are magic for both protons and
Theoretically, those numbers come about because nuclei have
a shell-like structure, said Dr. Witold Nazarewicz, a
nuclear theorist at the University of Tennessee and Oak
Ridge National Laboratory. Each shell can hold particular
numbers of protons and neutrons, and a nucleus is most
stable when its shells are precisely filled up, leading to
the magic numbers.
The highest known magic number for neutrons is 126, meaning
that common lead, with 82 protons and 126 neutrons in its
nucleus is the heaviest known "doubly magic," or extremely
stable, isotope in the periodic table.
"The question is, what is the next doubly magic nucleus
beyond lead?" Dr. Nazarewicz said.
Those numbers should help map out what Dr. Nazarewicz
prefers to call generically a "region of stability" among
the superheavies. (Because, he says, it could resemble a
peninsula more than an island.) Various theories have
suggested that the next magic proton number is 114, 120 or
126, he said. There is general agreement that the next
magic neutron number is 184, he said.
The new experiments by the Livermore and Dubna scientists
created forms of element 115, for example, with at most 173
neutrons, suggesting that they are still short of what
could be a land of strange new forms of matter.
Rather than being round, nuclei in that region and beyond
could contain bubbles and have strange doughnut-like
shapes, Dr. Nazarewicz said.
They could also have unpredictable chemical properties.
The new work should shed light on whether theories of those
undiscovered bits of matter are correct or not, he said.
"Those discoveries tell us a great deal about the
underlying nuclear structure," Dr. Nazarewicz said. "About
how the very heaviest systems are built - how they tick."
Dr. Darleane C. Hoffman, a nuclear chemist at the
University of California, Berkeley, also cautioned that the
new findings would have to be checked out by other
laboratories. But she said the value of the work was
"Scientifically, just for the pure science of it, wouldn't
you like to know just how many chemical elements there
are?" Dr. Hoffman said. "And until you actually have a
measurement that you believe and you can confirm, you don't
have any idea whether the various models the theorists
propose have any meaning at all."