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Registered Member #4237
Joined: Tue Nov 29 2011, 02:49PM
Location:
Posts: 117
Hi everyone.
I've got a Geiger-Müller tube that I can't seem to act like I want it to. First, the schematic. It's very simple:
Now, as a gamma photon passes through the GM tube (got a Cs-137 sample providing about 10 counts/s), it will short out, and I should read about 500 * 220/10220 = 10.7V. My problem here, is that I read closer to 50V! I am certain the oscilloscope is showing the correct value, and both resistors are the correct value, checked with independent multimeters. My HV supply is providing exactly 500V, and I have attempted to replace the GM tube.
Nothing fixes it! I've got no more ideas left. What could be wrong?
The anode of the tube has a capacitance by itself. When the tube fires, this is discharged into the 220k resistor. Whether this is a viable explanation depends on the size of the capacitance and on the duration of the discharge.
Registered Member #4237
Joined: Tue Nov 29 2011, 02:49PM
Location:
Posts: 117
Shrad wrote ...
or maybe your setup reacts to the radiation, like a transistor or something in the PSU
is everything shielded well enough? I guess a simple plastic case transistor would react under radiation, no?
The radiation is not nearly intense enough for the electronics to get affected in any measurable way.
Proud Mary wrote ...
Does the GM tube have a type number and a datasheet? This is the place to start.
It's called ZP1200, but there's no datasheets on it.
Uspring wrote ...
The anode of the tube has a capacitance by itself. When the tube fires, this is discharged into the 220k resistor. Whether this is a viable explanation depends on the size of the capacitance and on the duration of the discharge.
I guess that makes sense. Not sure how I would fix it.
Anyways, I worked around the problem by replacing the 220k resistor with a 220k varistor, and reading the signal out at a varistor value that fit. So consider this problem solved!
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GM tube woes, help needed :(
