Geiger counter, home made!

[JohnDoe19700101]

Hello!,

I have built a geiger counter using the SI-3BG russian tube with the following data:

380-460VDC operation voltage so: i have tuned mine to 420V since i have come to understand that you should be in the middle of the operation plateu.
0,015-0,02mkA i guess that is 15-20µA.

:
Working Range of Dose Power 300R/h
Working Voltage 380-460V
Working Current 0,015-0,02 mA
Plateau Length/ Inclination 80V/0,25%/V
Sensitivity to Gamma Radiation 188 - 235 Pulses/s/R/h
Own Background 0,2 Pulses/s
Working Temperature Range -50 +60 С
Length 55mm
Diameter 10mm
:

However i cant seem to get any readings from it i have it connected to the 420V on the annode and 470k to GND on the cathode hopeing to detect someting on my DVM over the 470k.

here is a conceptual shematic of my design in PNG.

I accually have 7 villard cascade steps with 100nF caps and 1N914 Diodes.

And currently you can ignore the led/speaker step in the corner, its not done yet.
I removed the 21Mohm resistor since it gave me 20µA trought but gave a wierd Voltage drop to exactly 137V between GND and annode. Could have been that the DVM is loading the circuit..

Can anyone tell me why I am supposed to have it in the middle of the Voltage platue!?
Maybe link some resources about the physics of the GM tube.
And is my GM tube data too bad to get background radiation readings?
Seems like the annode is having 0,0µA current constantly like i get no disharge...

Cheers JD.

 

[kak111]

Anode resistor for this tube is 10Mohm...20Mohm
Cathode resistor depends on load 220kohm...1Mohm
Normal DVM loads HV-circuit and cant give right values.
Remember that tube output is very short pulses.

example circuit...



The HT is connected to the Geiger-Muller tube via R12. IC3 with associated components provides pulse shaping
with 22us integration and differentiation time constants. IC4A produces a 230us pulse for the speaker.
The input thresholds of IC4A act as the pulse discriminator. The Q output of IC4A turns TR3 on to drive the speaker.
The outputs of IC4A should not be used to drive a counter circuit because the maximum count rate will be limited.
Instead, IC4B can be used connected to the output of IC3. The time period should be set to about 10us.

Teralab - Geiger Counter Electronics

**broken link removed**

 

[JohnDoe19700101]

Ok thx, kak111!

I thought as much, so i will do some tweaking..