PING: Steve Willner
F/32 Eurydice
The following article should be interesting to you.
Neutrino experiment shows that radioactivity does not heat earth's
core
Using a delicate instrument located under a mountain in central Italy,
two University of Massachusetts Amherst physicists are measuring some
of the faintest and rarest particles ever detected, geo-neutrinos,
with the greatest precision yet achieved. The data reveal, for the
first time, a well defined signal, above background noise, of the
extremely rare geo-neutrino particle from deep within Earth.
The small number of anti-neutrinos detected, however, only a couple
each month, helps to settle a long-standing question among
geophysicists and geologists about whether our planet harbors a huge,
natural nuclear reactor at its core.
Geo-neutrinos are anti-neutrinos produced in the radioactive decays of
uranium, thorium, potassium and rubidium found in ancient rocks deep
within our planet. These decays are believed to contribute a
significant but unknown fraction of the heat generated inside Earth,
where this heat influences volcanic activity and tectonic plate
movements, for example. Borexino, the large neutrino detector, serves
as a window to look deep into the Earth's core and report on the
planet's structure.
Borexino is located at the Laboratorio Nazionale del Gran Sasso
underground physics laboratory in a 10 km-long tunnel about 5,000 feet
(1.5 km) under Gran Sasso, or Great Rock Mountain, in the Appenines
and operated by Italy's Institute of Nuclear Physics. The instrument
detects anti-neutrinos and other subatomic particles that interact in
its special liquid center, a 300-ton sphere of scintillator fluid
surrounded by a thin, 27.8-foot (8.5-meter) diameter transparent nylon
balloon. This all "floats" inside another 700 tons of buffer fluid in
a 45-foot (13.7-meter) diameter stainless steel tank immersed in ultra-
purified water. The buffering fluid shields the scintillator from
radiation from the outer layers of the detector and its surroundings.
Neutrinos and their antiparticles, called anti-neutrinos, have no
electric charge and a minuscule mass. Except for gravity, they only
interact with matter via the weak nuclear force, which makes them
extremely rare and hard to detect, as neutrinos do not "feel" the
other two known forces of nature, the electromagnetic and the strong
nuclear force.
Borexino is one of only a handful of such underground detectors in the
world and is supported by institutions from Italy, the United States,
Germany, Russia, Poland and France. Designed to observe and study
neutrinos produced inside the Sun, it has turned out to be one of the
most effective observatories of its kind in the world, with 100 times
lower background noise, in part due to extremely effective
scintillator purification and use of radiation-free construction
materials.
Borexino is not the first instrument to look for geo-neutrinos. In
2005, a Japanese-United States collaboration operating a similar
detector in Japan was able to identify some of these rare particles.
But those measurements were affected by radioactive background noise,
anti-neutrinos emitted from several nuclear reactors operating in
Japan.
The small number of anti-neutrinos detected at Borexino, only a couple
each month, helps to settle a long-standing question among
geophysicists and geologists about whether our planet harbors a huge,
natural nuclear reactor at its core.
Based on the unprecedently clear geo anti-neutrino data, the answer is
no, say the UMass Amherst physicists.
"This is all new information we are receiving from inside the Earth
from the geo-neutrino probe," Cadonati explains. "Our data are
exciting because they open a new frontier. This is the beginning. More
work is needed for a detailed understanding of Earth's interior and
the source of its heat, with new geo-neutrino detectors above
continental and oceanic crust."
In the future the international researchers hope that observations
from similar detectors in Canada, Japan and Borexino in Italy can be
coordinated to improve geo-neutrino detection and analysis even
further.
Adapted from materials provided by University of Massachusetts
Amherst.