Picture of How to see alpha particles
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. Originally I thought that this may be an effect of Cherenkov radiation, but since alphas cannot go fast enough to cause this, something else is going on. The sensor on the camera can detect single high energy photons. Americium does emmit small amounts of gamma, but mostly it is an alpha emitter. What may be happening is alpha particles are hitting the CMOS and interacting with it and possibly creating very small amounts of Bremsstrahlung radiation which the sensor is able to see. This is a very fun and relatively easy project

Learning Goal: The goal of this project was to learn about radioactive decay, and how it interacts with different mediums.

Now before I continue, a brief note on safety.


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. 

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.

Judges see last step for contest info.

Look closely at the video and you should see the small white flashes, the tell-tale sign of alpha particles interacting with the CMOS.

Doctor90250 7 months ago
I've seen a lot of americum 241 experiments and often wondered if you could reproduce the effect of flashing lights experienced by astronauts when cosmic rays pass through the retina at the optic nerve junction. after seeing your instructable, i placed my phone camera directly over a sample, turned brightness up, and sure enough saw the little white specs flashing on my screen. My wife failed to see why this was so exciting, and reminded me once again what a nerd i am....LOL
djsamm881 year ago


harderm2 years ago
A follow-up project: Someone suggested you may be viewing 'noise' in the form of stray gamma rays or beta particles. Gamma rays are highly energetic x-rays, which like photons of light are uncharged. Beta particles are electrons, with negative charges. But alpha particles, which are the 'signal' of interest in this experiment, have a double positive charge. How can we tell these apart? A magnetic field of sufficient strength will deflect positive and negative charges in opposite directions. Gamma rays will pass straight through a magnetic field without changing direction. Go online or to your library and look up the average energy of the alpha particles emitted by the Americium. From that, can you design a magnet (permanent or electro-) whose field is in the right direction and strength to bend your alpha particles a convenient distance in a known direction in the webcam? Compare the position of the flashes with and without the magnetic field. How many are + charges or -charges? How many pass straight through? If you reverse the direction of the magnetic field, it will deflect the charged particles in the reverse direction. That way, the total deflections will be 2x as great as in the experiment with only one field direction. You may have to create a device to record the positions of the flashes to do this accurately. The device you will have built is called a mass spectrometer. With it, the energies of charged particles from different sources can be compared.
Higgs Boson (author)  harderm2 years ago
This sounds like a very interesting project! I will definitely do this when I get the time. thanks for the suggestion. One thing though is the flashes are not concentrated into one area, so It is likely a collimator would need to be made and then the magnetic field added. as there is very limited space in the webcam I am unsure it would all fit. If it doesn't maybe a alpha source in a vacuum chamber (to increase its range) and a alpha sensitive phosphor at the other end would be a better setup. I guess then it wouldn't be testing whether the webcam is seeing alpha or gamma though. Maybe a better way is to place something in front of the americium that would stop alpha but let gamma through (like a piece of paper or something) and see if the flashes stop (which they should).
poofrabbit2 years ago
Hey congratulations on being a finalist in the hack it contest! Good luck to you!
Higgs Boson (author)  poofrabbit2 years ago
Thank you!
you could also try to see the alpha particles by the trails they will make. i have not done what i will describe here but i think it would work. get the americium alpha source( i've tried to extract nuclear energy from these before, search americium experiment on youtube) and place it in some sort of transparent chamber containing water droplets in a state where all they need to form a cloud is a nucleation site. trails will be formed where the particles provide nucleation sites.
It sounds like you are describing a cloud chamber. Most of them use alcohol rather that water because it evaporates faster, and is generally easier to get in a state of super-saturation. But yeah placing the americium in a cloud chamber will work very well for seeing the tracks.
simpleplan3 years ago
Nice project.

You are almost certainly not detecting Cherenkov radiation, which is the equivalent of a sonic boom for light. This requires highly relativistic particles, and heavy alphas are very non-relativistic. Most likely you are just seeing the alphas hitting the CMOS sensor directly. They produce electron-hole pairs as they lose their kinetic energy plowing through the silicon, and that mobile charge is what the sensor fundamentally detects.
Higgs Boson (author)  simpleplan3 years ago
Thanks. I'll do some more research and update the info.
2gooey3 years ago
I would have to agree with simpleplan. As a suggestion for a project similar to this, I recommend building a cloud chamber. In a cloud chamber you can directly see particles traveling and interacting with the medium, and it is fairly inexpensive to build as well.
Higgs Boson (author)  2gooey3 years ago
Oh yeah! I have had lots of fun with cloud chambers! I did this because I really wanted to make something with the webcam that has been sitting around my room for a really long time. Plus I didn't want to buy dry ice.
wakojako3 years ago
Looking at the video I'm doubtful that you were actually detecting alpha particles. I reckon you were just picking up gamma and beta due to the low rate of flashes.
Maybe your webcam has a small glass filter on the cmos.
Higgs Boson (author)  wakojako3 years ago
From what I have read, Americium does not emit any beta, and only a very small amount of gamma. From what I have read however, gamma cannot cause Cherenkov radiation, so the latter statement seems much more likely, however, after watching some videos i have taken in a very dark room, I noticed a few flashes every second, that were smaller so couldn't be seen well in the light.
Your idea about a random number generator is good,
Radioactive decay is often used for True Random Number Generators,
due to the truly random nature of radioactive decay.

The one problem though is generally the detector set up uses Geiger-Muller tubes/detectors, which are far from inexpensive.
Your setup, though might take some Processing/ coding.... would be a much better setup.
Higgs Boson (author)  BrefelanDesigns3 years ago
The only thing stopping me is my lack of experience, but I'm sure with a little dedication it could be working.