Recently I was playing around with the electronics of a plasma globe, same as from tesla coils, while randomly measuring background radiation with my 300E+ in the vicinity for an unrelated reason. The counter immediately freaked out like crazy! Upon further investigation I observed that the counter has to be within 15inches to the tesla-thing to produce a value. The closer it gets the more it measures.
Now I'm wondering if this is x-ray radiation, gammaray or just the radio interference. (Electrical discharges of tesla coils can produce radioactivity. But I don't know how much.) I think it's mostly radio interference throwing high energy electrons at the tube. (A test with a very strong magnet held at the tube showed no weird behavior but the speaker was humming. Done just for clarification) I tried overdoing it so I got me a fluorescent lightbulb. It's also heavily smelling like ozone so there is ionizing radiation, obviously.
I am certain that I am producing at least a little bit of x-rays. I would like to know how much. Is it possible to get a reading of it if put the counter inside a makeshift faraday cage or am I wrong and plain electrical interference doesn't manipulate the measurements meaning; high doses radiation?
Update: I tried to eliminate the possibility that electrical interference is causing this values. Therefore I built a Faraday cage and put the counter inside.
And unfortunately it displays no more than normal background radiation. :( But at least the faraday cage is working perfectly. :D
Interesting experiment. I know that, in theory, a Tesla coil can generate X-rays. I'm not sure how much though since it's certainly not the most efficient way to generate them. Your Faraday cage proves that in your setup, the registered counts were probably interference on the PCB.