Interactions News Wire #61-05
27 July 2005 http://www.interactions.org
Source: Berkeley Lab
Content: Press Release
Date Issued: 27 July 2005
An html version of this release with images and links to additional
information is available athttp://www.lbl.gov/Science-Articles/Archive/NSD-KamLAND-geoneutrinos.html
FIRST MEASUREMENT OF GEONEUTRINOS AT KAMLAND
Results from KamLAND, an underground neutrino detector in central Japan,
show that anti-electron neutrinos emanating from the earth, so-called
geoneutrinos, can be used as a unique window into the interior of our
planet, revealing information that is hidden from other probes.
"This is a significant scientific result," said Stuart Freedman, a
nuclear physicist with a joint appointment at the Lawrence Berkeley
National Laboratory (Berkeley Lab) and the University of California at
Berkeley, who is a co-spokesperson for the U.S. team at KamLAND, along
with Giorgio Gratta, a physics professor at Stanford University.
"We have established that KamLAND can serve as a unique and valuable
tool for the study of geoneutrinos with wide-ranging implications for
physical and geochemical models of the earth," Freedman added.
In a paper presented in the July 28, 2005 issue of the journal/Nature,/
an international collaboration of 87 authors from 14 institutions spread
across four nations has demonstrated the ability of the KamLAND
detectors to accurately measure the radioactivity of the uranium and
thorium isotopes, the two main sources of terrestrial radiation. The
measurements the collaborators made are in close agreement with the
predictions of the leading geophysical models of our planet's thermal
KamLAND's geoneutrino experiment was funded by the U.S. Department of
Energy's Office of Science, and the
Japanese Ministry of Education, Culture, Sports, Science and Technology.
Surprising as it may seem, for all that we have learned about far
distant astrophysical events like deep-space supernovae, dark energy, or
even the Big Bang itself, the interior of our own planet remains a
mysterious and largely unexplored frontier. Among the many questions is
the source of terrestrial heat. The total amount of heat given off by
the earth at any given moment has most recently been estimated at about
31 terawatts (TW). A terawatt is equivalent to one trillion watts. For
comparison, the average energy consumption of the United States at any
given moment is 0.3 trillion watts.
Much of this heat is re-radiated energy from the sun, but nearly half is
produced from the earth's interior. Radioactivity is known to account
for some of this heat, but exactly how much has been difficult to say
because, until now, there has been no accurate means of measuring
radiogenic heat production.* *These latest experimental results from
KamLAND indicate that is no longer the case.
"Our results show that measuring the flux of Earth's geoneutrinos could
provide scientists with an assay of our planet's total amount of
radioactivity," said Freedman. "Measuring geoneutrinos could also serve
as a deep probe for studying portions of the planet that are otherwise
inaccessible to us."
Said Stanford's Gratta, "There are still lots of theories about what's
really inside the earth and so it's still very much an open issue. The
neutrinos are a second tool, so we're doubling the number of tools
suddenly that we have, going from using only seismic waves to the point
where we’re doing essentially simple-minded chemical analysis."
Added physics Professor Atsuto Suzuki, director of the Research Center
for Neutrino Science, vice president of Tohoku University and
spokesperson for the Japanese team at KamLAND, "We now have a diagnostic
tool for the Earth's interior in our hands. For the first time we can
say that neutrinos have a practical interest in other fields of science."
Dennis Kovar, Associate Director for Nuclear Physics of DOE's Office of
Science, agreed with Suzuki. "I believe the results of the multinational
KamLAND collaboration are very interesting and indicate that science has
a new, powerful tool for peering deep into the core of our planet."
KamLAND stands for Kamioka Liquid scintillator Anti-Neutrino Detector.
Located in a mine cavern beneath the mountains of Japan's main island of
Honshu, near the city of Toyama, it is the largest low-energy
anti-neutrino detector ever built. KamLAND consists of a weather
balloon, 13 meters (43 feet) in diameter, filled with about a kiloton of
liquid scintillator, a chemical soup that emits flashes of light when an
incoming anti-neutrino collides with a proton. These light flashes are
detected by a surrounding array of 1,879 photomultiplier light sensors
which convert the flashes into electronic signals that computers can
analyze. The photomultipliers are attached to the inner surface of an 18
meters in diameter stainless steel sphere and separated from the weather
balloon by a buffering bath of inert oil and water which helps suppress
interference from background radiation.
Neutrinos and their anti-matter counterpart, anti-neutrinos, are
subatomic particles that interact so rarely with other matter they can
pass untouched through a wall of lead stretching from the earth to the
moon. Neutrinos are produced during nuclear fusion, the reaction that
lights the sun and other stars. Anti-neutrinos are created in fission
reactions, such as those that drive nuclear power plants, and in
radioactive nuclei, such as uranium and thorium, that emit an electron
and an anti-electron neutrino when they decay.
Anti-neutrinos, like neutrinos, come in three different types or
"flavors," electron, muon and tau, with the anti-electron neutrino, or
geoneutrino, being by far the most common. Geoneutrinos can be detected
and measured at KamLAND via a distinctive reaction signature after the
subtraction of anti-neutrinos captured from nearby reactors and in
background events from alpha particles.
"KamLAND is the first detector sensitive enough to measure geoneutrinos
produced in the earth from the decay of uranium-238 and thorium-232,"
said Freedman. "Since the geoneutrinos produced from the decay chains of
these isotopes have exceedingly small interaction cross sections, they
propagate undisturbed in the earth's interior, and their measurement
near the earth’s surface can be used to gain information on their sources."
In measuring geoneutrinos generated in the decay of natural radioactive
elements in the earth's interior, scientists believe it should be
possible to get a three-dimensional picture of the earth's composition
and shell structure. This could provide answers to such as questions as
how much terrestrial heat comes from radioactive decays, and how much is
a "primordial" remnant from the birth of our planet. It might also help
identify the source of Earth’s magnetic field, and what drives the
The U.S. team at KamLAND includes researchers from Berkeley Lab, UC
Berkeley and Stanford, plus the California Institute of Technology, the
University of Alabama, Drexel University, the University of Hawaii,
Louisiana State University, the University of New Mexico, the University
of Tennessee, and the Triangle Universities Nuclear Laboratory, a
DOE-funded research facility located at Duke University, and staffed by
researchers with Duke, North Carolina and North Carolina State
Berkeley Lab is a U.S. Department of
Energy national laboratory located in Berkeley, California. It conducts
unclassified scientific research and is managed by the University of California.
Visit our Website at www.lbl.gov/
For more information contact:
Freedman 510-486-7850 or email@example.com
Giorgio Gratta, Physics: (650)
725-6509 and cell (650) 387-9658, or firstname.lastname@example.org
Atsuto Suzuki, Research Center for
Neutrino Science, Tohoku University, Japan: +81-22-795-6720 and +81-22-217-5123,