So You Want To See Alpha Particles With Your Eyes PART 5
Visually, this is the most boring way to see alpha particles (or their impact on the physical world at least) in my series. It's also the easiest and cheapest. Unlike my previous 4 posts on this subject, there will be no need for: high voltage; dry ice; Geiger-Mueller tubes or even simple phosphors slopped onto a glass slide.
Nope! All this project takes is any old cheap webcam-and source of alpha radiation. You'll also need a desktop computer to run the webcam with, and a couple screwdrivers.
At my local Disabled American Vets resale shop (kind of like the Salvation Army shops) they have a big box of webcams for .99 cents each! In previous posts I pried the IR filter off of one to make an infrared camera. This time we're prying off the lens in addition to the IR filter.
The steps were simple: take out the screws of the casing. Rip off the lens bezel. Unscrew the lens completely out.
Here's where webcams differ: some have the IR filter as the last part of the lens: the end that is normally inside the camera. Hold the lens at different angles and if you can see green/red coatings that's probably the IR filter. If not, there will be a teeny-tiny little greenish piece of glass inside the camera that used to nearly touch the inside end of the camera. Anytime I've ever taken a webcam apart this filter has always just fell out for me. Sometimes you'll have to pry it out.
Next, all you do is set it up in a dark container and lay an alpha particle source onto the CCD chip of the camera: BOOM! You'll get little white and blue dots zinging all over. Lift off the alpha source and no more moving spots or specs.
I experimented many times, placing and removing the alpha radiation source and starting at my computer screen. The dots disappear when the alpha source is removed. A couple times they did not come back--it turns out I had the alpha source (I have many) flipped around the wrong way: flip it face down onto the CCD and the moving dots returned.
Here's a video showing radiation on and off: I edited down, but the results were the same for dozens of tests: radiation shows up as white and blue dots zinging around. Removing the radiation results in no dots. Placing radiation sources upside down showed no-greatly reduced amounts of dots.
The results are similar to my alpha sphinthariscope only I don't have to wait 10 minutes for my eyes to adjust to darkness-and I don't have to shove my eye inches away from a pile of radioactive material! Let the webcam get blasted in the face with radiation.
The mesmorizing waves of dots and dashes looks like the surface of a lake at night during a full moon in the sphinthariscope, in my webcam alpha particle detector it's more hit or miss. The moon reflected in a small puddle.
The webcam's CCD is way more high-tech than the sphinthariscope though.
CCD stands for "Charge-Coupled Device" and are the sensor that "sees" in many webcams. These pure silicon dioxide is used to change photos to electrons. Light to digital information. Many times these are "doped" with other chemicals to give the silicon dioxide a better affinity for certain inputs. There are different types of dopants, but webcams use "P" dope, which can use our friends from the last post: indium and gallium! Those two help snatch infrared light.
In my last post I mentioned the super lattice of eutectic alloys. There is a similar theory in CCDs where the crystal lattice is missing a component and this empty spot grabs electrons and helps move them around over and over again as a charge carrier. The 'hole' moves all around as the electrons keep moving to file the hole, which leaves a new hole.
This is actually the function of MOSFET and MOS transisistors: like a quantum bug-zapper waiting for photons. Then they carry this info down to the actually CCD which just digitizes this information. So really, the MOSFETs do the interesting work of "seeing".
OK hole, slide me toward the CCD!
A couple more times and then the Meowfet will dump it's charge to the CCD and then it's sent to a pixel!
Ouch! Crammed into a dead pixel square again.
