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The Question
(Submitted October 30, 2006)
Can you see cosmic rays? My dad told me about a science project he saw when
he was in school that involved dry ice, a fish tank, and an iron, and maybe
something else. With this set-up you can actually see cosmic rays. I found
this very interesting and want to learn more about it.
The Answer
Thanks for your excellent question. Cosmic rays are generally single atoms or
particles that are produced from supernovae events when a star dies. These
tiny particles get to very high energies (fractions of the speed of light)
and occasionally some of them reach the Earth. Most of these particles are
deflected by the Earth's magnetic field or scatter in the Earth's atmosphere,
but particles called muons can reach the ground. Hundreds pass through your
body per second! You can read more about cosmic rays at our website:
http://helios.gsfc.nasa.gov/
Now almost 100 years ago, scientists discovered that muons leave a trail in
a super-cooled, super-saturated mist (water vapor) that can be observed. The
device that was first used to produce these trails is called a cloud chamber,
see:
http://en.wikipedia.org/wiki/Cloud_chamber
The trail that is formed when a charged particle (muon) passed through the
cloud chamber is likely what your Dad observed. We don't actually see the
particles themselves (much too small), but we can see the trail of ionized
gas that is produced as muons pass through the gas chamber. In fact, you or
your classroom can actually build a cloud chamber without too much difficulty,
see:
http://www.lns.cornell.edu/~adf4/cloud.html
Hope this helps,
Georgia and Mike
For "Ask an Astrophysicist"
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