How is nuclear chemistry used in smoke detectors?

1 Answer
Mar 17, 2014

Most household smoke detectors use the alpha particles emitted by radioactive americium-241.


Ionization smoke detectors use the alpha particles from americium oxide, #"AmO"_2#, to detect smoke. One gram of #"AmO"_2# provides enough material for more than three million smoke detectors.

The plutonium-241 in spent nuclear fuel decays to form americium-241. The Am-241 decays by emitting alpha particles and low energy γ rays to become neptunium-237.

#""_95^241"Am" → ""_93^237"Np" + ""_2^4"He" + γ#

The alpha particles collide with the oxygen and nitrogen in air in the detector's ionization chamber. This produces charged particles (ions). A low-level electric voltage applied across the chamber collects these ions. A small, steady electric current flows between two electrodes.

When smoke enters the space between the electrodes, the smoke particles attach to the charged ions. The ions lose their charge. The number of ions — and thus the electric current — falls and an alarm goes off.