Detectron Geiger Counter

[Baron]

Chris F. Inscribed thus:

At this point, I think you're right - it's probably issue with the B+
supply, probably a combination of poor filtering and inadequate output
current. After tracing out the schematic that's about the only
conclusion I can come to.

Since you get clicks when the tube is not connected, have you checked
the EHT supply. It probably has bad caps in there. Something breaking
down as the EHT rises.

 

[Baron]

Jeff Liebermann Inscribed thus:

Ummm... check out the gas and kerosene mantles from China. Some are
hot:

Incidentally, I once sacrificed one of my radioactive thorium Coleman
lantern mantles and ran a side by side comparison of the brightness
with a current non-radioactive zirconium mantle. The radioactive
mantle was MUCH brighter.


I like to use KCL (potassium salt, lite salt, or low-sodium salt). The
Potassium 40 is radioactive (450pCi/gram):
<http://802.11junk.com/jeffl/crud/salt.jpg>
<http://www.angelfire.com/electronic/cwillis/rad/nosalt.html>
It's not very hot but works well enough with a GM tube. Also lots of
fun going to the market with my 1950's GM counter. I once found some
brand of sea salt that was really hot, but it had been withdrawn or
recalled before I could return to buy some.

While at the market, try brazil nuts, acorns, and bananas. K-40 but
only when grown with massive overkill doses of fertilizer. Also try
cat litter. They all show up hot with my scintillation counter, but
are very weak with the GM tube.

If you go to the hardware store, check out the high phosphate
fertilizer. The stuff has uranium, K-40, thorium, radium, and who
know what else in it.

While at the hardware store, see if they have any tungsten stick arc
electrodes. They have some Thorium mixed in.

At home, if you have a dark colored granite counter top, you'll find
it somewhat radioactive from uranium.

The problem isn't so much the radiation. It's the radon gas that it
produces.

Got any pottery or kitchen plates with a yellow or bright orange glaze
(Fiestaware)? If so, they're uranium oxide.

Got any old cameras or eyeglasses made between WWII and about 1980?
Most lenses have thorium mixed into the glass to increase the index of
refraction. These are really weak and will only show up on my
scintillation counter.

Got a heavy scotch tape dispenser with a sand-epoxy mix in the base?
The sand has thorium mixed in.

Got an old static eliminator for removing the static electricity from
old vinyl records? If so, it's quite hot with Polonium.

More:
<http://www.kronjaeger.com/hv-old/radio/src/index.html>
<http://www.anythingradioactive.com/radsamples.htm>
<http://www.physics.isu.edu/radinf/natural.htm> See section on food.

Hey Jeff,
I've several old valves (Tubes) that are marked as containing "Radio
Active Material" with a "Do not Break Glass" and a yellow sticker on
them. CV number marking. Any ideas ?
They are stored in a box somewhere. If I can find them I'll come back
with the CV numbers.

 

[Chris F.]

Actually, the way this circuit is designed, any ripple or pulses in the DC
supply will be picked up and amplified the same way as pulses from the GM
tube. I guess it was never designed to operate on an AC power supply, but
I'm sure there's some way areound the problem.
I've replaced most of the capacitors (all are high voltage ceramics).

 

[Chris F.]

Hey Jeff,
I've several old valves (Tubes) that are marked as containing "Radio
Active Material" with a "Do not Break Glass" and a yellow sticker on
them. CV number marking. Any ideas ?
They are stored in a box somewhere. If I can find them I'll come back
with the CV numbers.

Probably cold-cathode rectifier tubes, equivalent to types like 0A2, 0D3,
etc. I have at least one American-made 0A2 that has a radioactive symbol on
the box, and the tube itself says "Contains less than 0.03 microcuries of
Krypton".

 

[Baron]

Chris F. Inscribed thus:

Actually, the way this circuit is designed, any ripple or pulses in
the DC supply will be picked up and amplified the same way as pulses
from the GM tube. I guess it was never designed to operate on an AC
power supply, but I'm sure there's some way areound the problem.
I've replaced most of the capacitors (all are high voltage ceramics).

Sods Law ! It will be the one that you didn't replace.

 

[tm]

Did you read the information in this link? Scroll down to the
discussion on the regulator tube.

http://www.dvq.com/geiger/heath_rc1.pdf

The 900 volt regulator tube operates in three regions; corona,
glow, and arc. It is sensitive to the high voltage supply conditions,
i.e. ripple can cause it to oscillate between the modes. Also, it is
sensitive to the filter capacitance.

 

[Chris F.]

I finally got this working, at least to the point where it's now usable. The
trick was to filter the B+ supply between the three tubes, with a
filter+inductor+filter combination, to prevent stray oscillation. It still
generates about 1 stray pulse every 5 seconds or so (not counting normal
background readings), but this may straighten out with some tweaking. Even
if not, the detector is now suitable for measuring above-background levels
of radiation, up to about 20 mr/hr. Should come in handy if the nearby
nuclear power plant ever blows....
Thanks to all for the advice.

 

[N_Cook]

I finally got this working, at least to the point where it's now usable. The
trick was to filter the B+ supply between the three tubes, with a
filter+inductor+filter combination, to prevent stray oscillation. It still
generates about 1 stray pulse every 5 seconds or so (not counting normal
background readings), but this may straighten out with some tweaking. Even
if not, the detector is now suitable for measuring above-background levels
of radiation, up to about 20 mr/hr. Should come in handy if the nearby
nuclear power plant ever blows....
Thanks to all for the advice.

So what have you found for a long-term test source , high enough emitter at
a
repeatable distance, to say give a count at least 5 times more than
background?
I've managed to lose my old broken gas-lighting mantle I had retained for
this purpose

 

[Jeffrey D Angus]

Should come in handy if the nearby
nuclear power plant ever blows....

Homer Simpson laughing at the "Run for the hills" alert level
on the warning sign at the power plant. "That will never happen."
Lenny asks him if he thought the power plant was safe. "No, if
the plant blows up, there won't be any electricity to power the
sign."

Jeff