Element number 95 is the end of the road for element collectors. The elements beyond here are both illegal to own and so radioactive that you wouldn’t want to own any of them anyway. In fact, the only reason Americium is legal to posses is that it was found to have an application in the civilian world which only uses a very small amount of actual material.

An ionization smoke detector.

Buried inside this smoke detector is a 0.9µCi Am-241 alpha particle source.

My sample of americium, like those of so many element collectors, is an ionization smoke detector. Within this unit (which was formerly in use in my bedroom before ceasing to function) is a small  ionization chamber containing 0.9µCi of americium-241. The alpha particles put out by the americium’s decay ionize the air in the ionization chamber. This ionization allows a minute electrical charge to pass between two electrodes in the chamber. If any smoke enters the detector, the ionized molecules in the chamber will bind to the smoke particles, thus decreasing the air’s ability to conduct the current. The smoke detector’s electronics sense this decrease and sound the alarm.

Americium is the only man-made element which is legal to posses, and the amazing part is that you can buy it for less than $10 at any hardware store. Moreover, 0.9µCi is by no means a wimpy sample. The americium in my smoke detector undergoes roughly 33,000 decays per second, and it cost next to nothing. Compare that to the 0.01µCi Pb-210 needle source listed under Polonium, for which I paid five times what I did for the smoke detector for only 1/90th of the activity, and it becomes apparent what an incredible deal this is.

Fortunately for those living with smoke detectors (but unfortunately for element collectors and radiation enthusiasts), the alpha particles emitted by the americium-241 are stopped by the steel or aluminum walls of the ionization chamber before ever leaving the smoke detector. Even without any shielding, they would only have a range of about an inch and a half in air. In other worlds, ionizing smoke detectors are perfectly safe to have in your home.

The americium does occasionally throw off a beta particle or gamma ray, but these events are rare enough that they are not a cause for concern. Also, the beta particles most likely don’t even get through the steel walls of the ionization chamber. This means that my Geiger counter (which can only detect beta and gamma radiation) gets no discernible reading above background from the intact smoke detector.

Supposedly, it is illegal  to disassemble an ionizing smoke detector in the United States, so a picture of the complete unit is all you’re going to get from me. If you’re absolutely dying to see what the americium in a smoke detector looks like, then you’ll have to look for someone who is brave enough to take one apart and then post about it on the internet. I recommend Theodore Gray’s (Mr. Gray’s page for americium can be seen HERE).


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