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Smoke Detectors
Two types ; Use of Photoelectric Effect
Use of Ionising Radiation
Amercium -241 in the form of Amercium Oxide
which is a decay product of Plutonium 241.
Plutonium 241 is formed inside reactors from
Uranium 238.
Half Life of 432 years and decays by emitting
alpha and gamma rays.
Smoke Detectors 2
Cost $1500 per gram but this is enough for 3
million smoke detectors.
How does it work
The alpha particles
ionise some of the
oxygen and
nitrogen atoms in
the air.
A voltage is applied
across the plates
and this causes the
charged particles
to be attracted to
either the negative
or positive plates.
This current keeps the
buzzer switched off.
How does it work 2
When smoke particles enter the chamber they
attach to the ions and neutralise them. Some
alpha particles are also absorbed by the
smoke particles causing less ionisation of the
air particles.
The current flowing between the plates drops
and the alarm then sounds.