Source for used Gieger counters
- If you are around ANY source that requires an insturment to be
reading that high a value, you are either in the industry(and you
would know there are far better meters for reading that level), or you
have alot to learn about radiation, it's effects, and how to avoid
just such a level at all costs. My $.02's worth. Phil N5TSX
--- In CDV700CLUB@yahoogroups.com, "teleronni" <telewinze@a...> wrote:
> A CD V-700 modified to read 50 r/hr would be ideal(?). Open to
- --- In CDV700CLUB@yahoogroups.com, "teleronni" <telewinze@a...> wrote:
> A CD V-700 modified to read 50 r/hr would be ideal(?). Open toLet me address this question from a technical standpoint.
True, most of us in this "hobby" want low range, high sensitivity
detectors and systems.
We have easily reached the maximum sensitivity allowed by nature and
physics, considering the ambient
background radiation, and have then exceeded that level by another
order of magnitude by building shields to
reduce the background.
There exists another portion of our "hobby" that are interested in
radiation detectors for other reasons than pure
science, at least to some extent or the other. These fall into many
subgroups, but we sort of lump them into
the "War Meter" category, that is high range, low sensitivity
Back in the Cold War days, the best technology available for a high
range meter was the ion-chamber.
These are embodied in the CDV-705 and CDV-71X series.
For some applications this remains true even today. Ion-chambers are
by nature typically less sensitive than a GM tube, but this is not
always the case. Certain designs, particularly the ones which operate
at a high internal pressure, can be quite sensitive.
In addition, these advanced designs share a common feature of all ion-
chambers, namely they have a tremendous dynamic
range, and react very similarly to all energies of gamma radiation.
GM tubes are not linear in the same way, and will respond
way differently to gamma rays of different energies unless they are
intentionally "energy compensated" by the addition of metallic
filters ( this also cuts the counts way back for certain energies-
basically the probe is reduced in overall sensitivity to match the
least sensitive area of its response curve)
I myself don't rely on the CDV-71X ion-chamber units much mainly
because they are SO insensitive, overall
operation can never be verified with civilian rad sources.
Lets now look at some common GM tubes, their maximum usable ranges,
some alternatives, and point out a few unusual instruments that may
fill both roles, science and war.
Pancake probe, LND 7311 my favorite for most science and
environmental rad measurements. Very sensitive, actually the
most sensitive of all 900V alpha-beta-gamma GM tubes> returns 60 CPS
for every 1 mR/H of Co-60
( a standard radiation source for almost all probe calibrations now).
60 CPS is 3600 CPM, derated to 3300 opn most scales, but
this tube tops out at about 166 mR/H, usable but not accurate to 200
Next in line would be the very common beta-gamma tube, LND Model 725,
used in Ludlum, Eberline and most other modern Hot-Dog probes. This
is the modern improved equivalent of the venerable 6993 of the
1960's. Beta-Gamma only, sensitivity of 20 CPS. Tops out at about 500
mR/H @600K CPM, in reality, limited to 200 mR/H.
Jumping way down in sensitivity is the LND Model 715 tube, giving a
return of only .5 CPS (30 CPM)per 1 mR/H. On a
Ludlum Model 3 meter, the max CPM readout is 500,000, so max reading
would be 16 R/H. Using a meter with a higher count range (X1000)
would allow an even higher reading to be taken, but not as much as
the range extension would indicate.
NOTE this is a 500V tube, not directly exchangeable with a 900V tube
until voltage is adjusted.
At the highest range, you would select something like a LND Model
7161, which gives .26 CPS and 32 R/H. This can even be extended to a
little higher if a special meter with a X1000 scale is used. Also a
Caveat: very high range GM tubes will do the job, but just like very
high range ion-chambers, can't be tested with civilian level rad
All GM tubes suffer from dead-time or paralysis issues at high end
making them non linear.
For a complete chart of all the LND tubes, arranged according to
their Gamma Sensitivity see:
Another company called Eurysis makes a line of small glass GM tubes
that are well suited to high range applications, but they have been
bought up by someone and I lost the link.
High Range Meters with built in probes:
Ludlum Model 14C. Has a connector for a typical external GM, but also
has an internal high range , energy compensated
GM that is good out to 2000 mR/H. Internal probe used only on the
Ludlum Model 5 Geiger Counter ( most others are actually ratemeters
or survey meters). 2 built-in high range energy compensated GM
tubes. Covers 0-2000 mR/H
Modern Ion-Chamber units with sound!:
Ludlum Model 9 > 0-5000 mR/H. Very cool, my favorite unit, can read
home lab strength sources on lowest ranges. Also can be tested using
a Beta source. Has Beta shield.
Ludlum Model 17 High Range Ion Chamber > 0-50,000 mR/H, my "war
meter", can actually detect civilian samples. Has Beta shield.
I think this was a zen riddle. There are two solutions,
one complex involving dealing with electronically driving & handling
an otherwise overdriven tube; and the simple one consisting
of a barrel of sand with the probe inside.
--- In CDV700CLUB@yahoogroups.com, "n5tsx" <n5tsx@n...> wrote:
> If you are around ANY source that requires an insturment to be
> reading that high a value, you are either in the industry(and you
> would know there are far better meters for reading that level), or you
> have alot to learn about radiation, it's effects, and how to avoid
> just such a level at all costs. My $.02's worth. Phil N5TSX
> --- In CDV700CLUB@yahoogroups.com, "teleronni" <telewinze@a...> wrote:
> > A CD V-700 modified to read 50 r/hr would be ideal(?). Open to
> > ieas/suggestions.
> > Thanks
- Why not this "surplus" tube as a spare? Whats the ups and downs?
PROBE 5980 THESE PROBES WERE USED IN THE SEVERAL MILITARY COUNTERS TO
EXTEND THE RANGE UP TO 500mR/hr. EASILY ADAPTABLE TO THE CDV-700 FOR
It's about $30 plus shipping.
--- In CDV700CLUB@yahoogroups.com, "DH" <revtkatt@y...> wrote:
> I think this was a zen riddle. There are two solutions,
> one complex involving dealing with electronically driving & handling
> an otherwise overdriven tube; and the simple one consisting
> of a barrel of sand with the probe inside.
> --- In CDV700CLUB@yahoogroups.com, "n5tsx" <n5tsx@n...> wrote:
> > If you are around ANY source that requires an insturment to be
> > reading that high a value, you are either in the industry(and you
> > would know there are far better meters for reading that level),
> > have alot to learn about radiation, it's effects, and how to avoid
> > just such a level at all costs. My $.02's worth. Phil N5TSX
> > --- In CDV700CLUB@yahoogroups.com, "teleronni" <telewinze@a...>
> > > A CD V-700 modified to read 50 r/hr would be ideal(?). Open to
> > > ieas/suggestions.
> > >
> > > Thanks
- Mr. Telewinz,
I think it might help everyone out if you mentioned why you want all
of this equipment in the first place. My guess is its for some type
of self protection type of thing, but I may be wrong.
If it is, I think you'll find that your standard CD V-700, coupled
with a CD V-715, 717, or 720, will be quite adequate for your
monitoring needs. There is no need to get your 700 to go up to 50
R/hr when a standard ion chamber meter will do that easily. You're
just overlapping ranges otherwise.
Again, if my assumption is correct, I suggest that if you haven't
already, try and get some high-range dosimeters (CD V-742 is most
common, but CD V-740 is just fine) and a dosimeter charger (CD V-750
is most common). I might also suggest that there is a lot of
commerical stuff out there, and on eBay, that is also excellent, but
doesn't come with the yellow paint and CD sticker. I'd take a PRDM 82
over a CDV anyday. Most importantly, all of the equipment you buy for
this purpose either needs to be serviced and calibrated by the person
you buy it from, or calibrated and serviced before you put it into
service. The only place I know of that calibrates with a "hot" enough
source is radmeters4u.com in Texas; the people who advertise on eBay
you mentioned earlier.
But, then again, most important thing to do is learn how to use them.
Hang around here for a while, I have for a few years now, and you'll
learn a lot. There's a bunch of reading materials on radiological
monitoring available on the internet as well.
I'm sure someyone here can tell you about the 5980; as I have no
experience with it.
- --- In CDV700CLUB@yahoogroups.com, "Ron" <telewinze@a...> wrote:
> Why not this "surplus" tube as a spare? Whats the ups and downs?TO
> PROBE 5980 THESE PROBES WERE USED IN THE SEVERAL MILITARY COUNTERS
> EXTEND THE RANGE UP TO 500mR/hr. EASILY ADAPTABLE TO THE CDV-700FOR
> RANGE EXTENSION.The QPL 5980 is a small thin wall tube for Gamma detection only. A
> It's about $30 plus shipping.
modern part number would be LND 726.
They both return 3.5 CPS per 1 mR/H. Used as the high range tube in
many wide dynamic range Military Geiger's.
3.5 CPS = 210 CPM, therefore with a CDV700, max reading would be
30,000 ( max range switch) / 210 =142 mR/H.
A LENi with X2 range extender switch would double that.
Clearly the CDV-700 based units are biased for very low,
environmental and science project ranges.
Ludlum Model 3 has a 0-500,000 CPM range, so could read out all the
way to 2380 mR/H ( 2.38R/H)
still not WAR METER material, but better than the original Military
capabilities ( .5 R/H)
Most of the commercial high range tubes use 500V, while the Military
versions all use 700V. CDV-700's use 900V and are not normally
This is not a deal breaker though, because I have developed an in-
probe adaptor that works very well:
From the meter jack, series a 3.3M resistor with a 1.8M resistor,
then run that to the tube. At the junction of the two resistors,
place a Zener Diode string to ground, of a value to equal the tube's
requirement ( say 700V). Now from the connection point on the tube,
run a .01 uF, 2000V capacitor back to the jack connection. The
resistors and Zeners drop the 900V down to that required by the tube,
while the capacitor shunts that DC network, passing the pulse back to
In most meters, this setup works perfectly, and is the basis for a
new probe I'm making, using those 480V Russian Pancakes!
One last thing, Lee Frank now advertises the 5980's for 19.99 USD on:
Note, his 7616 is also small and has 10 CPS per 1 mR/H.