How is nuclear chemistry used in smoke detectors?

1 Answer
Mar 17, 2014

Answer:

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

Explanation:

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.

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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.