Seeing alpha particles

A few months ago I deccided it was about time for me to actually do an experiment, which I hadn’t done in a while. There was one that I had heard about from many different sources and wanted to try.

Invent Geek as well as numerous videos on Youtube claimed that with just a smoke detector and a webcam you could indirectly see alpha particles. All you had to do was extract the americium 241 from the smoke detector and place it close to the sensor of the camera and you had yourself a device which could detect alpha particles.

Aside from sounding too good to be true, Americium is technically not an exempt source since its proton count exceeds that of uranium. However after seeing the price of other exempt sources online, and seeing how many people bend the rules, I decided it would not be a big deal.

Extraction of the americium from the smoke detector is relatively simple. There were no screws holding the plastic case together so I just pryed it apart with a couple of flat head screw drivers. From there I removed the PCB. The americium is housed an a bulky aluminum case which is held to the board with two solder joints. After desoldering those contacts the case was removed, exposing a plastic base with metal plate in the middle connecting to one pin of an IC. After desoldering the IC pin I broke of the tabs holding the plastic to the board, and carefully pushed the metal button out of the middle of the plastic base. This button has a thin foil of americium 241 on one side of it and that button is what I was after.013 021

Next was the webcam portion. Alpha particles (or a high energy helium nucleus) are very positively charged, and consequently have a habit of ionizing every atom they come across which takes a lot of energy. This means that not only do they have a range of only a few cm in Earth’s atmosphere, but they are also stopped by just about anything. Because of that, they are not able to go through the lens of the camera.

The lens on the camera i used just screwed right off (I used a $5 PC cam I found on amazon), and allowed me easy access to the cmos sensor to place the americium in front of. In fact, the back of the lens acted as a perfect place to mount the button. By simply gluing the americium to the back of the lens, I killed two birds with one stone. I got the sample close to the cam’s sensor with no barriers, and I blocked all the light that would have otherwise come through the lens.

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To put the finishing touches on the device I painted an old plastic container black and added that classic identifying symbol for all things radioactive.025

And now of course the most important part, the results. I plugged in the webcam to my computer and watched the screen. I was amazed and excited to be greeted by small flashes of light which are a result of the alpha particles hitting the sensor. I thought for a while the flashes may be the sensor detecting x-rays resulting from Bremsstrahlung, but more likely the particles are pulling electrons from the sensor resulting in an electron hole which causes a flash to occur on the screen. Either way it was a fun and pretty simple project.

I will try to post a video soon, but until then you can see more detailed instructions and a video on an instructable I made about this (I got first prize in their Hack it contest with this). Just go to instructables.com and search “how to see alpha particles.”

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