1.
The Bubble Chamber
The
first device used to see the tracks of charged particles
was the Cloud Chamber, developed in the Cavendish by
C.T.R. Wilson from 1894 and described to the Royal
Society in 1912. Cloud Chambers work because water droplets
will condense onto charged ions. The droplets are visible,
and follow the same path as the ionising particle.
However
it is difficult to make Cloud Chambers large enough
to observe trails from very penetrating, fast-moving
particles.
In
1952 the Bubble Chamber was invented by Donald A. Glaser
working at the University of Michigan in the United
States. The Bubble Chamber was "a new radiation
detector in which ionising events produced tracks consisting
of strings of tiny bubbles in a superheated liquid."
When a superheated liquid is suddenly expanded, boiling
will begin on ionised particles in the liquid. Passing charged
particles will produce these ions, so bubbles will mark
the path which the charged particles followed.
Bubble
Chambers can be built much larger than Cloud Chambers,
and have many other advantages. They produce sharper
tracks, as a liquid medium is more stable than the gas
in a Cloud Chamber. The Bubble Chamber only records
tracks made in a very short time interval, so the 'background'
of unwanted tracks is reduced. It can also be reset
very quickly, ready to record the next event.
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