Andrew Yee
July 28th 05, 04:53 AM
Communications Department
Lawrence Berkeley National Laboratory
Contact:
Lynn Yarris,
July 27, 2005
First Measurement of Geoneutrinos at KamLAND
BERKELEY, CA -- 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 activities.
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.
Our Mysterious Inner Planet
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 and Neutrinos
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
geodynamo.
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
universities.
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
http://www.lbl.gov
Additional Information
Stuart Freedman
510-486-7850
Giorgio Gratta, Physics
(650) 725-6509
Atsuto Suzuki
Research Center for Neutrino Science, Tohoku University, Japan
+81-22-795-6720 and +81-22-217-5123
KamLAND Websites with images can be accessed at
http://hep.stanford.edu/neutrino/KamLAND/KamLAND.html
and
http://kamland.lbl.gov/
The Japanese KamLAND Website can be accessed at
http://www.awa.tohoku.ac.jp/html/KamLAND/
[NOTE: Images supporting this release are available at
http://www.lbl.gov/Science-Articles/Archive/NSD-KamLAND-geoneutrinos.html]
Lawrence Berkeley National Laboratory
Contact:
Lynn Yarris,
July 27, 2005
First Measurement of Geoneutrinos at KamLAND
BERKELEY, CA -- 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 activities.
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.
Our Mysterious Inner Planet
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 and Neutrinos
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
geodynamo.
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
universities.
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
http://www.lbl.gov
Additional Information
Stuart Freedman
510-486-7850
Giorgio Gratta, Physics
(650) 725-6509
Atsuto Suzuki
Research Center for Neutrino Science, Tohoku University, Japan
+81-22-795-6720 and +81-22-217-5123
KamLAND Websites with images can be accessed at
http://hep.stanford.edu/neutrino/KamLAND/KamLAND.html
and
http://kamland.lbl.gov/
The Japanese KamLAND Website can be accessed at
http://www.awa.tohoku.ac.jp/html/KamLAND/
[NOTE: Images supporting this release are available at
http://www.lbl.gov/Science-Articles/Archive/NSD-KamLAND-geoneutrinos.html]