[Swlug] Back to the Geiger counter

[Rhys Sage]

I am keeping on with the Geiger counter project and running into very interesting issues.
Apparently the BPX61 photodiode can detect the 550nm light bursts from the Thalium-doped Cesium Iodide crystal I have though I have yet to see results. I do have a small Tritium capsule as a test subject. That emits just a shade above background radiation.
So far I have discovered that 1 gamma collision with the crystal will create one photon and the BPX61 will produce in response 1 electron. Given that my 100nf capacitor would need 5,620,000,000,000 electrons or radioactive particle hits. As 100CPM is really bad for somebody, 5.6 trillion is enough to really spoil somebody's day.
Clearly a smaller capacitor would help. The smallest commonly available is 1pf apparently and that would need 31.2 million gamma hits. Again, if that arrived in 1 minute then it would be a bad day.
I am really not sure there's any workaround to make a photodiode do the job. I have played with the bare photodiode and managed to sense light strongly through my finger using just a 2N3904 transistor. I should try the BC517 again but don't feel too optimistic. 
It could be the Tritium doesn't produce enough radiation and I need to put the sensor in the middle of a bunch of bananas (yes, bananas are radioactive).
The alternative seems to be a SIPM (silicone photo multiplier) and those things have to match the 550nm of the crystal. I'm researching that right now. Those things are more expensive than I'd considered. I'd never thought of components costing over $15 and some of those reach $50+
My bit of excitement today was a buck converter getting hot enough with a 9v battery, running the included circuit to be uncomfortable to the touch. 
I'll try the BC517 tomorrow id my eyes have recovered. Today I sat outside with mistress at Panera Bread and got thoroughly pollinated - as a result my eyes are burning and itchy.
Rhys Sage
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