On Mon, 4 Jan 2010, coffelt2 wrote:


"Kenneth Scharf" wrote in message
...
Geoffrey S. Mendelson wrote:
Kenneth Scharf wrote:

Once upon a time I recall the type CK1026 GM tube. This was about the
size of a 50C5 tube, but with a single pin and an aquadag coating on the
outside of the tube. This tube was used in a geiger counter project that
was in one of Alfred Morgan's 'boys books of radio and electronics',
either the 2nd or 3rd book. There were other types of GM tubes made, but
the CK1026 was one of the least expensive and was used in many simple
radiation detectors.

The ones used in the 1960's radiation detectors and then sold in a pack
of 3 for $1 at Radio Shack in the late 1960's looked like long neon bulbs
with an extra wire comming out of them. I think they were around two
inches
long, but it's been a long time since I've seen them.

Considering that they were designed to detect levels of radiation that
would
only exist if you were close to ground zero and poking your head out of
a shelter in the rubble of an east coast (US) city, for all I know they
really were neon bulbs. :-)

Geoff.

You probably could use a Neon bulb as a radiation detector. You'd have to
keep the tube in the dark (inside a black plastic box) and carefully adjust
the voltage across the tube so it was just below the firing voltage (need a
well regulated power supply). Then an alpha or beta particle might be
enough to trigger the tube into conduction. The sensitivity would be
determined how close to the firing voltage the bias supply was set.

I recall being unconvinced when a customer complained that the neon
lamp in his old, rotary disk type depth finder would not work at night
unless he shined a flashlight on it. He was absolutely correct, and
as time went on, we found that as all neon flash lamps (mostly NE2's
and NE51's I think) grew old and weak, they required a little extra
external excitation (flashlight worked ok) to light.

It's not so much that they needed light, but they could no longer light
up with the old value resistor. Changing the resistor would have worked,
as did the external excitation with a light.

That was the previous point, you put enough current into the neon bulb
so it's not quite lighting up, and then external radiation would excite
it. It's about setting a threshold right below where the bulb lights
up, and then any external excitation ignites it.

Michael VE2BVW