METHODS OF DETECTION AND MEASURING.
DETECTION BY WILSON CLOUD CHAMBER:-
The tracks of condensation produced by ionising radiations can be
detected in a cloud chamber, initially invented by C. T. R. Wilson, and
photographed. To the right is a photograph which shows the trails
produced by charged particles. These are curved due to the deflection
of the particle by the magnetic fields around the chamber.
MEASURING WITH A GEIGER-MULLER TUBE:-
H. Geiger and F. M. Muller invented a tube which was able to count the
particles emitted in a radioactive decay as pulses of electrical
current. The tube contains a low pressure gas (mainly argon) which has
a high voltage maintained across it. When a radioactive particle
enters through the thin mica window, it ionizes the gas and makes it
conduct which in turn creates a pulse of current. A ratemeter records
the count rate (the average number of pulses per second) of the sample.
In order to tell the radiations apart absorbing materials of different
thickness are placed between the source and detector.
Although there are now many other methods of detecting and measuring
radioactivity, the Wilson Cloud Chamber and the Geiger-Muller tube were
the first pieces of apparatus which made the breakthrough in the field.
Picture Sources -
http://www.hep.man.ac.uk/~mcnab/cloud/event.jpg
http://www.physics.sfsu.edu/~bland/courses/490/labs/b2/geiger.gif