Re: [Phys-l] Ionization type smoke detectors.

[Brian Whatcott <betwys1@sbcglobal.net>]

At 08:07 PM 9/27/2006, you wrote:
> According to: http://www.uic.com.au/nip35.htm
>
> " . . . 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?

Because the stopping power (mass per cross section area) of a
soot particle is greater than O2 or N2 ??

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

I'm guessing not on the basis of the same parameter.



Brian Whatcott    Altus OK    Eureka!