Smoke detectors

[Gonzolo]

I just noticed my new $10 smoke detector contains a few microcuries or less of radioactive Americium. Anyone one knows how these work? Why this element? It's the first time I see an application for it.

[Vern]

Google search string: smoke detector radiation yields this among the search results

Ionization chamber smoke detectors contain a small amount of radioactive material encapsulated in a metal chamber. They take advantage of the ions created by ionizing radiation to develop a low, but steady electrical current. Smoke particles entering the chamber disrupt the current and trigger the detector's alarm. Ionization chamber detectors react more quickly to fast flaming fires that give off little smoke.

I don't know why that element; probably it is cost efective and safe.

Keep on chuggin !!

Vern

[Zeteg]

If I remember correctly, Americium is pretty much the lowest decay of radiactivity. It emits quite a bit of alpha waves. There is a sensor that picks up the alpha waves, and thus the smoke detector doesn't ring. When the smoke is there, the waves are scattered, and thus it rings :)

It was a project I did quite some time ago, so I'm not sure if I'm completely right. Feel free to correct me.

[Crumbles]

Americium has a half life of 432 years! And also emits alpha particles which don't have a significant penetration depth: They get stopped by a simple sheet of paper. This would explain why it is safe!

Inside an ionization detector is a small amount (perhaps 1/5000th of a gram) of americium-241. The radioactive element americium has a half-life of 432 years, and is a good source of alpha particles. (http://home.howstuffworks.com/smoke2.htm)

[Gonzolo]

Thank you guys. Fun to see those funky elements are good for something.