| ▲ Mechanical |
The construction of this holder involves handling a radioactive source. Avoid touching the source directly and keep skin at least 5cm away from the front of the source, since this is the maximum range of the α particles. Because you're reading this, I assume you already have some knowledge of radioactive sources and are capable of handling them safely.
Safety rant over. I came across an old smoke detector in the attic a few days ago and thought it would be a nice little project to make a holder for the Americium 241 source inside the detector. Am-241 sources like these are pretty safe to handle, since they are relatively low activity and only emit α particles, which have quite a short range in air (around 5cm). Nevertheless, I made sure to always handle the source itself with tweezers and pliers, until it was mounted in the aluminium holder.
The source consists of a tiny disc of Americium 241 (about 2mm in diameter), which has been gold-plated and mounted in a small steel "button", 6mm in diameter. There is a 3mm spigot on the back of this, which enabled the source to be mounted on the smoke detector PCB. In the holder I made, the little spigot is held by a friction fit in a 3mm hole. An aluminium cap screws on the end to keep the source covered. The photos below should explain everything.
 Original source and PCB mount |
 Rear view |
 Source removed, front view |
 Source removed, rear view |
 Holder and cap |
 Closeup showing split. This provides enough spring to hold the spigot on the source tightly. |
 Source mounted in hole |
 With cap |
 Assembled |
 Warning label |
 Finished source. Overall size is 12mm dia., 45mm long |
10/06/11: See the effect this source has on a spark radiation detector.
20/12/13: Also see this being detected with a Geiger-Müller tube.
| ▲ Mechanical |