Mark Shwartz, News Service: (650) 723-9296, mshwartz@stanford.edu




Giorgio Gratta, Physics: (650) 725-6509 and cell (650) 387-9658,



Atsuto Suzuki, Research Center for Neutrino Science, Tohoku University,

Japan: +81-22-795-6720 and +81-22-217-5123, suzukia@awa.tohuku.ac.jp


The study, ``Experimental Investigation of Geologically Produced

Antineutrinos with KamLAND,`` appears in the July 28 edition of Nature.

Images are available at








EMBARGOED FOR RELEASE until Wednesday, July 27, 2005, at 1 p.m. U.S. Eastern

Daylight Time

Geologically produced antineutrinos provide a new window into the Earth`s



By Dawn Levy


In Jules Verne`s nineteenth century classic Journey to the Centre of the

Earth, an Edinburgh professor and colleagues follow an explorer`s trail down

an extinct volcano to the Earth`s core. Ah, fantasy! Here`s reality: For

more than a century after Verne wrote his novel, geophysicists have had only

one tool with which to peer into our planet`s heart-seismology, or analysis

of vibrations produced by earthquakes and sensed by thousands of instrument

stations worldwide. But now, geophysicists have a new tool for studying the

Earth`s interior, reported in the July 28 issue of the journal Nature.


That tool is a gift from unlikely collaborators-physicists who study

neutrinos, subatomic particles that stars spew out, and their antiparticles,

called antineutrinos, which emanate from nuclear reactors and from the

Earth`s interior when uranium and thorium isotopes undergo a cascade of

heat-generating radioactive decay processes. A detector in Japan called

KamLAND (for Kamioka liquid scintillator antineutrino detector) has sensed

the geologically produced antineutrinos, known as ``geoneutrinos.`` This new

window on the world that geoneutrinos open could yield important geophysical

information, according to the Nature paper`s 87 authors from more than a

dozen institutions and four nations.


``There are still lots of theories about what`s really inside the Earth and

so it`s still very much an open issue,`` said Giorgio Gratta, a Stanford

physics professor who with Stuart Freedman, a nuclear physicist with a joint

appointment at the Lawrence Berkeley National Laboratory and the University

of California-Berkeley, is co-spokesman for the U.S. part of the

collaboration. ``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



Said Freedman: ``This is a significant scientific result. 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.``


Added physics Professor Atsuto Suzuki, director of the Research Center for

Neutrino Science, vice president of Tohoku University and a spokesman for

the KamLAND experiment,  ``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.``


The Japanese Ministry of Education, Culture, Sports, Science and Technology;

the Japan Society for the Promotion of Science;  and the U.S. Department of

Energy funded the experiment.


Receiving their doctorates as a result of work reported in the paper were

two of the authors-Nikolai Tolich, a former Stanford doctoral candidate who

is now a postdoctoral fellow at the Lawrence Berkeley National Laboratory,

and Sanshiro Enomoto of Tohoku University.

In the dark to see the light


``How well do we know our planet?`` Gratta asked. ``We have very few

diagnostics. We only know essentially the crust of our planet. We can

measure mountains. We can sample rocks on the surface of the Earth. We can

drill holes a few kilometers deep and sample stuff down there, but in terms

of chemical analysis or what kind of rocks there are, beyond a few

kilometers, you simply don`t have access.``


What scientists can learn from seismology is limited. Seismic waves travel

through the planet as either compressional waves, which pulse like sound and

can travel through anything, or shear waves, which wobble side-to-side like

shaken jelly but cannot propagate in liquids, which cannot store the energy

needed to generate side-to-side motions. These waves travel at different

speeds and refract differently when they traverse the interfaces between

different types of rocks. So seismology gives information about the

locations of boundaries of different types of rock, Gratta said.


Geoneutrinos, in contrast, provide crude information about chemistry.

``Essentially [geoneutrinos reveal] just the chemistry of how much uranium

and how much thorium is there,`` Gratta said. ``You don`t know anything

about the crystal structure, whether the thorium is thorium oxide or thorium

nitride. But still, when you know nothing, knowing a little bit already

makes a big difference. This is really the first tool to actually do this.``


Scientists originally built KamLAND in 1997 to reproduce in the lab, using

antineutrinos from nuclear reactors, what they saw in nature with solar

neutrinos-the phenomenon that the three ``flavors`` of

neutrinos/antineutrinos ``oscillated,`` or turned into the other flavors, as

they propagated through space. They saw the same thing in both cases.

Previously neutrinos were thought to lack mass, but the oscillations told

them that neutrinos must have a very tiny mass-less than 500,000 times less

than that of an electron, Gratta said.


``That was a big deal because there`s lots of neutrinos in the universe, and

the mass of the universe is to some extent influenced by the mass of those

neutrinos,`` Gratta said.


Unlike the energetic sun, which is a gigantic generator of neutrinos, the

Earth emits only a modest number of antineutrinos-and scientists need a huge

detector to be able to see them. KamLAND was built with the size and

sensitivity required to detect Earth-made antineutrinos. In a cavern

underneath a Japanese mountain shielding the experiment from the background

noise of cosmic radiation, KamLAND consists of about 2,000 photomultiplier

tubes, each 20 inches (51 centimeters) in diameter and contained in a

59-foot (18-meter) vessel, bathed in 1,000 tons of liquid scintillator.


``Scintillator is essentially a mix of baby oil-lots of it-and benzene,``

Gratta explained.  ``To this cocktail you add a little bit of fluorescent

material. When particles interact with this cocktail, they make a little

flash of light that then is recorded by light sensors. These are the

photomultiplier tubes.``


The detector sees when particles arrive and measures their energies. Nuclear

reactors produce antineutrinos quickly-the detector sees about one a day.

The Earth is not so prolific-the detector sees about one a month.

Antineutrinos from nuclear reactors have a different energy spectrum than

those from the Earth`s interior, so scientists can tell them apart. Thorium

and uranium also have different energy spectra, so scientists can tell the

geoneutrinos made from each apart, too.

Future possibilities


What`s next? Bigger detectors are on many scientists` wish lists. A larger

detector would allow scientists to spot an event every few days instead of

one a month. Ideally, the detector would be far from nuclear reactors in a

location with well-characterized surface geology. Some scientists have

considered placing large detectors in mines in Australia, South Africa,

Canada and South Dakota. Others favor underwater detectors near island

systems such as Hawaii. ``The ocean water would shield cosmic radiation, and

the very thin oceanic crust would contribute little to the neutrino signal,

giving the best sensitivity to neutrinos from deep inside the planet,``

Gratta explained.


Norman Sleep, a Stanford geophysics professor, thinks geoneutrinos will

bring his field revolution, not evolution. Radioactive heat drives plate

tectonics, he said, and getting accurate ratios of thorium to uranium

isotopes will help scientists better understand deep-Earth processes. The

KamLAND results, while of limited statistical power, show a number of

neutrinos consistent with what`s expected from existing models, the Nature

authors wrote. ``Now we`ll be able to resolve the Earth as a sphere,`` Sleep



``It`s a revolution,`` Gratta agreed, ``but let me temper this a little bit

with the physicists` point of view-that is, those are very difficult

measurements and those detectors are very expensive and large. So before the

revolution really comes to fruition, I think it`ll take some time, I would

imagine one or two decades, before we have more of those detectors and maybe

larger ones built in the appropriate place for geophysics.``


Researchers from the following KamLAND collaborating institutions also

participated in the study: University of Alabama, California Institute of

Technology, Drexel University, University of Hawaii-Manoa, Kansas State

University, Louisiana State University, University of New Mexico, University

of Tennessee, Duke University, University of North Carolina-Chapel Hill,

North Carolina State University, Beijing Institute of High Energy Physics,

University Bordeaux I and CNRS (France).

- 30 -

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