[ RadSafe ] Article" Geoneutrions show U and Th decay is a driving heat force

John Jacobus crispy_bird at yahoo.com
Thu Jul 28 08:34:39 CDT 2005

The following was reported on PhysicsWeb at
Geoneutrinos make their debut
27 July 2005

The KamLAND experiment in Japan has detected neutrinos
produced by radioactive decays deep inside the Earth
for the first time. The experiment, which is located
in a mine 1000 metres below ground, has detected
electron antineutrinos from the beta-decay of
uranium-238 and thorium-232, and placed an upper limit
on the heat generated by these processes. If the
accuracy of the measurements can be improved it may be
possible to use "geoneutrinos" to probe the Earth's
interior (Nature 436 499).

Neutrinos are very difficult to detect because they
are electrically neutral and only interact weakly with
matter, which means that they can pass through
thousands of kilometres of matter without being
absorbed. The Kamioka Liquid scintillator antineutrino
detector (KamLAND) comprises a balloon with a diameter
of 13 metres contains about 1000 tonnes of liquid
scintillator. It identifies antineutrinos by counting
the number of telltale flashes of light that are
produced when antineutrinos occasionally collide with
protons in the liquid to produce a positron and a

KamLAND Picture

The amount of light produced by the positron allows
the energy of the neutrino to be determined, which
enables the KamLAND team to distinguish between
neutrinos from the decay of uranium and thorium and
background neutrinos. Using this method, the
experiment detects about one geoneutrino per month.
The background sources include neutrinos produced by
nuclear reactors, which have been used in other
experiments to explore the fundamental properties of

The KamLAND results have already been used to place an
upper limit on the heat generated by uranium and
thorium inside the Earth. "Unlike previous estimates,
which are based on indirect samples from meteorites,
this is based on a direct measurement of the neutrinos
produced by the decay of these isotopes," team member
Nikolai Tolich told PhysicsWeb. "The heat generated by
uranium and thorium decay is the driving force for
mantle convection, and hence plate tectonics and
earthquakes. This result and future measurements using
the same technique will provide useful inputs to Earth
convection models." 

Radiogenic heat in the Earth graph

"We now have a diagnostic tool for the Earth's
interior in our hands," added KamLAND spokesman Atsuto
Suzuki. "For the first time we can say that neutrinos
have a practical interest in other fields of science."

"Every now and then a man's mind is stretched by a new idea and never shrinks back to its original proportion." -- Oliver Wendell Holmes, Jr.

-- John
John Jacobus, MS
Certified Health Physicist
e-mail:  crispy_bird at yahoo.com

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