Ouch Sparky! Well if you must have a visual show I suggest abandoning the dangerous HV and going for a Cloud Chamber. They are easy to build and the thickness of the vapor trail makes it easy to distinguish between alpha, beta or gamma (cosmic) radiation. As a child I saw my first cloud chamber at a Russian technology exhibit at the New York Coliseum back in the late 1950's. Both the Soviet Union and that NY exhibition hall are long gone.
Why publish something so useless? Your alpha source would need to be actually sitting on the metal plate to show activity. Alpha particles, even high energy particles, are stopped by our surface layer of dead skin. If you've ever used a cloud chamber you would know that alpha particles are stopped by a few inches (the size of the project) of air.
A counter circuit would be very easy to implement. A Geiger counter works in an identical way, except that there is some gas inside a Geiger tube. There is both analog and digital means to do the job. Of course, without a known standard, you couldn't calibrate it. Although this is a cool gadget to play around with and for educational purposes, does it have any practical use? I understand that skin, and even paper stops alpha particles. That's why an alpha source (Americium, I think) is used in smoke detectors.
Just right, Beth. Build a big enough one and you wouldn't need fireworks. I am not sure that would be safer, though.
Long ago I worked on spark and wire chambers. I even helped with a needle chamber. In those cases we wanted to see the track of any charged particle, so we had a chamber of a noble gas. This ionized and the spark followed the ionized trail. This simple detector is a great little project. Now all we need is a cirsuit to count the particles. Next project?
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