Is your House Radioactive?

Is your house radioactive? By that I mean, do you have anything radioactive in your house? Interestingly enough, state law requires you to have an item in your house which is radioactive!

"Crazy talk!" You say.

Oh ho ho... no, not at all, I'm serious. It's a little known fact, but the smoke alarm in your house works via radioactive materials.

It clearly states this on the back of every smoke detector. Just peel that sucker off the wall and start reading all the small print. Sooner or later you will find wording like"...contains x amount of Americium-241 (Am-241), a radioactive material...".

Most people are unaware of this fact, and that is why I tell you-so you can impress your friends. In reality it isn't much to worry about. The smoke alarm works by detecting a steady stream of alpha particles. If smoke passes in between the alpha emitter and alpha detector, the stream of alpha particles is disrupted and an alarm goes off.

I just checked the amount of Am-241 in my smoke detector, and it said it contained 0.9 micro curies of Americium-241. I know that probably doesn't mean anything, but let me try to put it into perspective. A Curie is a measure of radioactive material, it represents decays per unit time. A decay (aka disintegration) is when an atom of Americium expels, in this case, an alpha particle.

Like I said before, my smoke detector contains 0.9 micro Curies (uCi) of Americium-241. Since I know 1 uCi= 2.22 x 10^6 decays per minute, we can figure out that my smoke alarm expels about 2 million alpha particles per minute! Or 33,300 disintegration's per second! It sounds crazy, but that is a pretty small number in nuclear science. Before you remove every smoke detector from your house, realize this-alpha particles cannot even pass through the smoke alarm container. Due to their 2+ charge and size they are highly interactive, and even if one nailed you dead on, it wouldn't be able to penetrate your skin.

The only way an alpha emitter can do you harm is if you ingest or inhale it, because once it's in you it's going to deposit all of it's energy into your body. This is how the Russian spy, Alexander Valterovich Litvinenko, was killed. However, the nuclide at fault was Polonium-210, not Am-241 (and I think it was a quite a bit larger dose than in your smoke alarm).

Well, hope you learned something! Check out my other blog entries in the blog archive to the right (might be up a little too!).