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[Phys-l] Ionization type smoke detectors.

According to:

" . . . The alpha particles emitted by the Am-241 collide with the oxygen and nitrogen in air in the detector's ionisation chamber to produce charged particles called ions. A low-level electric voltage applied across the chamber is used to collect these ions, causing a steady small electric current to flow between two electrodes. When smoke enters the space between the electrodes, the alpha radiation is absorbed by smoke particles. This causes the rate of ionisation of the air and therefore the electric current to fall, which sets off an alarm. . . . ."

1) Why is the current reduced sufficiently when a small fraction of CO2 molecules is mixed with air?

2) Would an alarm also be triggered by presence of unburned (from a leak) cooking gas in air?

Ludwik Kowalski
Let the perfect not be the enemy of the good.