[ RadSafe ] Article: US proposes a beam of neutrinos to measure the density of the Earth's core

[John Jacobus]

>From  http://physicsweb.org/articles/news/9/2/9

................
Neutrinos for geophysics
16 February 2005

A physicist in the US has proposed using a beam of
neutrinos to measure the density of the Earth's core.
Walter Winter of the Institute for Advanced Study in
Princeton says that neutrinos could provide
information about the Earth that is not available with
other techniques (arXiv.org/abs/hep-ph/0502097).
Although measurements of the seismic waves produced by
earthquakes can be used to reconstruct a profile of
the Earth's interior, they provide only indirect
information.

Neutrinos come in three flavours -- electron, muon and
tau neutrino. They are also electrically neutral and
only interact weakly with other particles, which means
that they can pass through thousands of kilometres of
matter without being absorbed. However, neutrinos can
change flavour or "oscillate" as they pass through
matter with, for instance, electron neutrinos
oscillating into muon neutrinos and so on. Since the
amount of oscillation depends on the electron density
in the matter, and since the electron density is
directly related to the overall matter density, it
should be possible to determine the matter density of
the Earth by making accurate measurements of the
oscillations. 

[Figure in article]

Winter proposes sending a beam of neutrinos from an
accelerator tens of thousands of kilometres through
the Earth to a detector on the other side of the
globe. In principle, the beam would travel from a
proposed "neutrino factory" in the northern hemisphere
to a 50,000 ton iron detector in the southern
hemisphere. For example, a beam could be sent from
CERN in Switzerland through the inner core of the
Earth to a detector in New Zealand (see figure). 

The first "long-baseline" neutrino oscillation
experiment was performed in 1999, when neutrinos were
sent through the ground from the KEK laboratory in
Japan to the SuperKamiokande detector 250 kilometres
away. Plans are also underway to send beams from
Fermilab near Chicago to the Soudan lab in Minnesota,
710 kilometres away, and from CERN to the Gran Sasso
National Laboratory in Italy, 730 kilometres away. 

The main challenge would be building the neutrino
factory with a vertical decay tunnel so that the beams
passed down through the centre of the Earth. Existing
neutrino beams are only a few degrees below the
horizontal, whereas the beam that Winter is proposing
would have to travel directly downwards. However, he
is confident that such an experiment could begin by
2035. 

In 2003, physicists at KEK also proposed using
neutrino beams to destroy nuclear weapons and last
year, an astrophysicist in the US suggested using one
of Jupiter's moons to detect neutrinos.

About the author
Belle Dumé is Science Writer at PhysicsWeb



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"Baltimore is actually a very safe city if you are not involved in the drug trade."
DR. PETER BEILENSON, the city's health commissioner.

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


		
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