GM_counter_schematic.JPG (190821Bytes)
This is my second Geiger counter version. The picture below shows the Geiger counter prototype:
The GM tube and the transformer modem are from Sparkfun. I have slightly modified the original schematic, taking the impulse from the cathode of the tube, not from the anode, and added a Schmitt trigger to get a clear TTL output signal for counting.
The Geiger tube has a mica window for alpha radiation. I used americium-241 from a dismantled ionization smoke detector to test the Geiger counter. Americium-241 is a so called alpha emitter and has a half-life of 432 years. About one percent of the emitted radioactive energy of 241Am is gamma radiation.
I have attached a video as well to show some testing. I will use the Geiger counter for our weather balloon experiment to measure cosmic radiation.
https://www.youtube.com/watch?v=6mGqd_USBEY