Sunday, September 9, 2012

Detecting alpha particles with a modified webcam

After some interesting messages in CDV700Club, I decided to do a quick experiment with a spare webcam. Is it possible to detect alphas with a DRAM memory? What about other devices?

I saw on the net some people claiming to detect alpha particles with a webcam, but none of them modified the camera to allow the alpha particles to hit the sensor.

Alpha particles does not have too much range, maybe up to 5cm in air, and almost anything can stop them, so the first thing you must to do if you want to detect alphas is to allow them to reach the silicon. In other words, you must to remove the glass in front of the sensor.

I had a spare webcam I could sacrifice for the experiment. I planned to remove the front glass by side impact, but as you can see, something did not work as expected. The glass got broken just in front of the light sensitive area and some small pieces of glass were deposited over the chip itself. To check if the device was damaged, I plugged it into the computer and surprise! The camera was still alive:

The next step was to check the camera in darkness. Everything was ok, except some damaged pixels:

So, the next step was to put in front of the sensor an alpha source. Results were quite evident:

Each white point in the image is the detection of one alpha particle, and you can see dozens of them in any photogram. To get an idea of how it looks in real time, look at this video:

After some tests, I conclude the webcam detects only alpha particles. It does not respond to betas or gammas, only alphas, and maybe some exotic particles, like muons from cosmic rays.

So, do you like to build your own alpha particle detector? Get a cheap webcam (CMOS or CCD, they both work fine), disassemble it and remove carefully the front glass from the sensor. How? Well, use your imagination, but maybe some work with a Dremel will suffice. Do not damage the chip! just remove the front glass.

Once removed, cover the chip with dark mica film (blocks light but let alphas to pass) and congratulations for your new alpha detector!


  1. Brilliant!! Can't wait to try this one myself.

  2. Or pyrolytic graphite, this also works well.
    Thin it down to about 0.01 mm, if possible.
    I use wet and dry 4000 grit sandpaper then an acetone rinse and air dry.
    This also gets the fingerprints off, which is important as they block alphas to some extent.


  3. I tried to "chip" the two glass cover sandwich (IR filter and cover glass)...and tore the CCD off the board! Good thing it only cost me $2.00. I'd like to do this with a small P&S camera so as to have self-contained recording device too. Monochrome CCDs/cmos would be better as it wouldn't have the Bayer colour filter built onto the surface of the sensor.

  4. Doesnt the Mica film shield the sensor from alphas ? Normally some um of material is enough to do so....

    1. Nope. A thin mica window is what alpha sensitive geiger tubes uses. It seems to be quite "transparent" for alpha particles (as well as for light).

  5. Hi, I've since refined my pyrolytic graphite discovery and it does suggest some new physics going on.
    Its very sensitive to the exact type of graphite though so might explain why some people have reported that it doesen't work as well for them, the sort you want needs to have no flaws or bubbles :-)
    Hope this helps the folks trying this, also try harvesting the camera from a Mac 22" as these have bare CMOS sensors as well and the filters don't seem to cause much of a problem.

  6. bad time for webcams ! thanks Miguel for the info !

    JM F5VLB