Geiger Muller Tube that Glows

That would be a good guess....

"If a poor diatomic gas quencher were introduced to the tube, the positive argon ions, during their motion toward the cathode, would have multiple collisions with the quencher gas molecules and transfer their charge and some energy to them. Neutral argon atoms would then be produced and the quencher gas ions would reach the cathode instead, gain electrons in excited states which would decay by photon emission, thereby producing spurious tube discharge as before. However, effective quencher molecules, when excited, do not lose their energy by photon emission but by dissociation into neutral quencher atoms. No spurious output pulses are then produced."

http://en.wikipedia.org/wiki/Geiger%E2%80%93M%C3%BCller_tube

Thankyou SolarEagle.

maybe you over exposed it to radiation or the fill gas leaked out

I suspect the tube may have been subject to impact and though I cant see any damage I think glass tube integrity is in doubt. Thanks for your post.

Here is a source for cheap in price GM tubes. the usual disclaimers. If you buy make sure to match your working voltage of 675

www.goldmine-elec-products.com/products.asp?dept=1473

That looks like a struggling Ion pump tube to me. Are you sure this is supposed to be a GM tube?

Yes its a G.M. tube inside my U.K. made Nuclear Enterprises geiger counter. I think its faulty and will have to find some other tube to put in its place. Not heard of an ion pump before... I will look those up. Thanks for reply.

Do you have a part number and make printed on the tube?

Measure the leakage resistance using low voltage - below 200V to see if there is some leakage current flowing which is greater than 10nA. Normally GM Tube operate at voltage above 300V.

It may be Vacuum Ion gauge but as you have said you have removed it from Geiger counter, then that doubt is baseless.

Thanks very much... very interesting reply. Its a Centronics B6TS which I think runs on 675 volt. I should have included that information with my first post I suppose. Thanks.

Tank Circuit:

This is sure a Gamma counting GM Tube and it leaves no doubts about it now.
Its operating zone is 625V to 725V with 100 V near linear zone. 675V is the center point on that line which is the prescribed operating point.

Spark occurring means quenching gas which is generally a Halogen gas or combination gas has leaked out of the tube or it may have Organic quenching gas which has limited use life time. Leakage spark current will run > 100uA and this must be seen in high voltage supply DC current display.

You can modulate power to the tube to quench the tube. ON time and OFF time switched by switching the high voltage supply to create a dead time in the tube. 1kHz switching may be all right.

You can also send tube to the manufacturer to repair it.

These things don't affect Halogen quenched GM Tubes

Large short time over voltage

Large short time radiation exposure

Reversal of high voltage polarity

There is about a 400V potential in the tube.

texasron:

At 400V, this GM Tube will be either in proportional zone with multiplication factor ranging from 10 to 100 and depending on Gamma Energy and flux it will have number of ionized charge carriers. With leaked out GM Tube to air, it may have further reduction in number of ion pairs due to larger ionization potential of Nitrogen and Oxygen.

If one is getting a glow without exposure to Ionizing Radiation then applied voltage must be much higher as spark zone comes after GM Zone.

With 400V DC applied to this tube no spark should ever appear even if tube is leaked out or its gas depleted or it is cracked. Electrode spacing is about 5mm and that requires 5kV to spark over with gas leaked out and being at NTP air.

Something is wrong somewhere. Look for problems in DC bias supply. It might have lost regulation and might be at much higher voltage due to damage to the feedback resistors used for sensing high voltage or someone tempered the voltage control potentiometer.

You may be wrongly measuring the high voltage in a multimeter which has 1M impedance and it will load and lower the voltage reading and as soon as you remove the probes, the HV will be more than double. You may be operating the GM in spark zone.