The principle of a cloud chamber is easy to understand,
and you can build one in your spare time !
real
cloud chamber movies of cosmic rays and radioactvie decay from
a Japanese science museum.
The chamber is filled with air, and is supplied with
a fast evaporating liquid like alcohol. The air quickly becomes
saturated with alcohol vapor, a gas, to the point where any slight
disturbance will cause some of those gas molecules to condense
to a liquid.
When a high-energy particle passes through this saturated
air, it ionizes air molecules. These charged air molecules provide
"condensation nuclei". That is, they provide lots of
tiny places for the alcohol vapor to condense, or turn to liquid.
So tiny droplets of liquid form, showing the path of the original
high energy particle.
These chambers were used in research by taking photographs
of the trails, like the one below. The different types of trails
are created by different types and energies of particles. In general,
vertical trails are likely to have come from cosmic rays, and
the density, thickness, length, and scattering of the trail can
be used to characterize the particles as well. And these chambers
can be placed in magnetic and electric fields to cause particles
to curve.
Bubble chambers work on similar principles, but rely
on a liquid (not water) which is ready to "boil" or
vaporize with the slightest encouragement in the form of ionized
molecules as a starting point. Bubble chambers have certain advantages
because liquids are so much denser than the air in a cloud chamber,
more interactions take place. There are a number of interesting
things in the bubble chamber photograph ....
