I’ve been looking for a simple experiment I could do involving physics that I already had all of the materials for. After a bit of searching online I came across a project on inventgeek.com using a webcam and smoke detector, and of course I had to build it. basically you will be able to see small white dots flash on the screen where alpha particles were. Although you do not technically see the alpha particles directly, what you do see is the indirect effect of the alpha particles via Cherenkov radiation. Cherenkov radiation occurs when either alpha particles, beta particles, or positrons pass through a dielectric medium faster than light can travel through that medium. The particles will disturb the energy levels of the electrons in the dielectric medium, and as the electrons return to their original state they emit a photon, which is what you see as the flashes on the screen. This is a very fun and relatively easy project.
Now before I continue, a brief note on safety.
THIS PROJECT USES A SMALL AMOUNT OF RADIOACTIVE MATERIAL.
A small radio active source extracted from a smoke detector is used. It should not be too much of a concern, but it is not to be taken lightly. The sample is made is made from Americium-241, which is a strong alpha emmiter. At atmospheric pressures alpha particles can only travel a few centimeters, but do take caution.
DO NOT SWALLOW THE SAMPLE
DO NOT CARRY THE SAMPLE IN YOUR POCKET
AVOID HANDLING THE SAMPLE LONG PERIODS OF TIME
LIMIT YOUR EXPOSURE BY NOT KEEPING THE SAMPLE NEAR YOU AND STORING IT IN A STEEL OR ALUMINUM CASE
MAKE SURE THE CASE IS CLEARLY MARKED TO PREVENT OTHERS FROM HANDLING IT
Okay that being said I take no responsibility something bad happens doing this project. So long as you use common sense it should be fine.
A while ago one of our smoke detectors stopped working. There was a short in it somewhere which caused it to go off in the middle of the night one night. Needless to say it was removed very swiftly, and was laying in our basement until I rediscovered it, and decided to use it for this project. Unfortunately I do not have pictures of the dismantleing process, but it is relatively simple.Pretty much all smoke detectors are like this. If there are screws unscrew them. If not pry it apart with a flat head screwdriver. Once inside you can cut wires to the battery and piezo buzzer, and remove the PCB, you are looking for a bulky aluminum case. It is pretty obvious. This case is connected to the board by two solder joints, so fire up your iron and desolder the two joints until the case falls off. You should see a plastic case stuck to the board, with a metal plat on top. That plate should be connected to a chip underneath, so desolder that and pry the metal plate off. look on the back of the PCB for three plastic bits poking through some holes going to the plastic case, and break them off. Remove the case, and there should be a small metal button in a hole in the center of the plastic. use pliers to pull it out from the back side of the plastic case. This is the radioactive material so be careful with it. try to avoid touching it directly, and keep it in a clearly labeled metal case until you use it. ALWAYS WASH YOUR HANDS WELL AFTER HANDLING THE SAMPLE EVEN IF YOU DON'T DIRECTLY TOUCH IT!
Almost no modifications need to be done to the webcam of this project. You won't be able to put the sample behind the camera lens sense it will block the alpha radiation (paper is all it takes to stop alpha particles), so I mounted it on the other side of the lens. On my cam the lens just screwed right off, allowing me to easily glue it onto the back side of the lens. Be sure that you glue the sample with the Americium foil facing the CMOS (the foil side has a slight indent). Apply glue (Elmer's will work fine) to the back side of the lens, and place the back side (not foil side) of the sample onto this. I placed a notecard on top of this to stop the alpha radiation as it dried. Once the glue has dried, screw the lens back on. the sample glued on the lens was enough to block all of the outside light, and the seal between the lens and PCB was good enough to block light from the LEDs. If you have power LEDs or something inside creating too much light, you can desolder them add some jumpers and reroute them outside the enclosure, if you need to block more outside light you can add an enclosure to help block more. I technically didn't need to, but I wanted to make mine look a lot cooler.