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From: F/32 Eurydice on 4 Apr 2010 07:55

The following article should be interesting to you.

http://bit.ly/9nLpPk

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.
From: Steve Willner on 7 Apr 2010 13:50
In article <aefb0bf2-deab-4c3d-8ffa-d57438031620(a)l25g2000yqd.googlegroups.com>,
"F/32 Eurydice" <f32eurydice(a)sbcglobal.net> writes:
>The following article should be interesting to you.

The OP is right that the topic interests me, but I wish people would
post links to refereed papers or preprints rather than news articles
or press releases. Such sources are very often misleading.

The preprint is at http://lanl.arxiv.org/abs/1003.0284
The article has apparently not yet been accepted for publication.

>Neutrino experiment shows that radioactivity does not heat earth's
>core

I'm afraid that's not what the actual paper shows.

>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.

Make that the second time... a Japanese experiment was first. But
it's still an interesting result.

>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.

This part is accurate; a _reactor_ (at least one that contributes
much power) is ruled out. I don't think the idea of a nuclear
reactor was ever popular, but the paper puts a 95% confidence limit
on its output of 3 TW. For comparison, the previous upper limit on
reactor output was 6 TW, and the thermal output due to radioactive
_decay_ is, as far as I can tell, 30 TW.

Table 3 of the paper shows that the geo-neutrino output is actually
_above_ that expected from models but only by about one sigma. (The
models say that most of the power comes from radioactive decay, and
the rest comes from residual heat of Earth's formation.) Better data
will be needed to provide real checks on the models but should be
obtainable.

Another result of the paper is additional strong evidence for
neutrino oscillation.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123 swillner(a)cfa.harvard.edu
Cambridge, MA 02138 USA
From: Yousuf Khan on 7 Apr 2010 18:12
Steve Willner wrote:
> In article <aefb0bf2-deab-4c3d-8ffa-d57438031620(a)l25g2000yqd.googlegroups.com>,
> "F/32 Eurydice" <f32eurydice(a)sbcglobal.net> writes:
>> 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.
>
> This part is accurate; a _reactor_ (at least one that contributes
> much power) is ruled out. I don't think the idea of a nuclear
> reactor was ever popular, but the paper puts a 95% confidence limit
> on its output of 3 TW. For comparison, the previous upper limit on
> reactor output was 6 TW, and the thermal output due to radioactive
> _decay_ is, as far as I can tell, 30 TW.

So what you're saying is that of the 30 TW of radioactive decay
happening naturally inside the Earth, only 3 TW comes out of the core?

> Table 3 of the paper shows that the geo-neutrino output is actually
> _above_ that expected from models but only by about one sigma. (The
> models say that most of the power comes from radioactive decay, and
> the rest comes from residual heat of Earth's formation.) Better data
> will be needed to provide real checks on the models but should be
> obtainable.
>
> Another result of the paper is additional strong evidence for
> neutrino oscillation.

I'm always puzzled by how they can even tell whether a neutrino is
coming from inside the Earth, from a nuclear power plant, from the Sun,
or from a supernova somewhere. A neutrino is a neutrino, how can they
distinguish where it's coming from? Didn't they also say at one time
that the Sun was producing less neutrinos than they expected? We
definitely know that the Sun must be mainly powered by nuclear
reactions, and not by something else.

Yousuf Khan
From: F/32 Eurydice on 8 Apr 2010 09:42
On Apr 7, 1:50 pm, will...(a)cfa.harvard.edu (Steve Willner) wrote:
> In article <aefb0bf2-deab-4c3d-8ffa-d57438031...(a)l25g2000yqd.googlegroups..com>,
>  "F/32 Eurydice" <f32euryd...(a)sbcglobal.net> writes:

> the paper puts a 95% confidence limit on its output of 3 TW.

Is 3 TW enough to account for the heat balance of the earth?

From: Steve Willner on 8 Apr 2010 18:15
In article <4bbd0360$1(a)news.bnb-lp.com>,
Yousuf Khan <bbbl67(a)yahoo.com> writes:
>So what you're saying is that of the 30 TW of radioactive decay
>happening naturally inside the Earth, only 3 TW comes out of the core?

No, not at all. The distinction is between radioactive decay, which
has to occur for every radionuclide, and a reactor, i.e., nuclear
fission. Standard models of Earth's interior include radioactive
decay but no fission. I gather there has been speculation that
fission might be occurring, but according to the paper, fission can't
be more than 10% of the radioactive heat.

There's more at
http://en.wikipedia.org/wiki/Geothermal_gradient
but I'm not enough of an expert to verify much of the article. I
didn't spot anything that looks obviously wrong, though.

>I'm always puzzled by how they can even tell whether a neutrino is
>coming from inside the Earth, from a nuclear power plant, from the Sun,
>or from a supernova somewhere.

That's in the paper. Separation of decay neutrinos and reactor
neutrinos is by energy, which is measured in the experiment. Solar
and supernova neutrinos aren't mentioned; I'd assume they are
negligible in this experiment. The geo-reactor measurement isn't
discussed in detail -- the authors seem to consider it a minor result
-- but it comes from subtracting the expected power reactor neutrinos
from the observed reactor neutrinos.

> Didn't they also say at one time
>that the Sun was producing less neutrinos than they expected?

That was a problem for, what, 30 years or so? The answer is neutrino
oscillations. Neutrinos measured on Earth are only 1/3 of the ones
emitted by the Sun because the "flavors" have mixed by the time the
neutrinos reach Earth.

More at
http://en.wikipedia.org/wiki/Solar_neutrino_problem

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123 swillner(a)cfa.harvard.edu
Cambridge, MA 02138 USA
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