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Smoke Detector.
The radioactive source in a smoke detector is americium-241
an a
emitter.
The a-particles
ionise the molecules of the air
forming ions and electrons which are attracted to a pair
of charged plates.
When the ions and electrons hit the
plates
they provide a small amount of
electricity.
This amount of electricity doesn't
change and is monitored by the
smoke alarm.
When smoke enters the detector, the smoke
particles
near to the radioactive source
absorb many of the a-particles
before they can ionise the air
between the charged plates.
The number of ions and electrons
between the plates decreases
and so the amount of electricity (current)
which is passed between the plates
also decreases.
The smoke detector notices the
decrease in current and sets off
the alarm.
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Copyright © 2008 Dr. Colin France. All Rights Reserved.