Q: Calibrating a 1962 CD Radiation Meter

[Norm Dresner]

Among the stuff in my father-in-law's basement I found a '1962 "Radiological
Survey Meter" which the manual says is only sensitive to gamma radiation.
"It is designed to be used by radiological Civil Defense personnel
in determining radioactive contamination levels that may result from an
enemy attack or other nuclear disasters."

It's claimed sensitivity runs from around 0.2 to 500 "roentgens per hour".
After changing the battery -- astoundingly for that era it's a single
pentode hybrid vacuum tube & single transistor circuit that runs on a
single D-cell -- it passed it's built in self-check which, according to the
schematic, just assures that the electronic circuitry is working close to
its design point. Since I'm not in a university and don't have any "radium
or Cobalt 60" laying around the house (AFAIK), I'm stumped as to finding a
method of determining if this thing still works. I'd appreciate suggestions
for either a Q&D function-test or a real calibration with a safe source of
around 4 r/hr of gamma radiation.

TIA
Norm

 

[Michael Dombrowski]

Among the stuff in my father-in-law's basement I found a '1962 "Radiological
Survey Meter" which the manual says is only sensitive to gamma radiation.
"It is designed to be used by radiological Civil Defense personnel
in determining radioactive contamination levels that may result from an
enemy attack or other nuclear disasters."

It's claimed sensitivity runs from around 0.2 to 500 "roentgens per hour".
After changing the battery -- astoundingly for that era it's a single
pentode hybrid vacuum tube & single transistor circuit that runs on a
single D-cell -- it passed it's built in self-check which, according to the
schematic, just assures that the electronic circuitry is working close to
its design point. Since I'm not in a university and don't have any "radium
or Cobalt 60" laying around the house (AFAIK), I'm stumped as to finding a
method of determining if this thing still works. I'd appreciate suggestions
for either a Q&D function-test or a real calibration with a safe source of
around 4 r/hr of gamma radiation.

TIA
Norm

I certainly am no expert in radiation meters, but I seem to recall
radioactive marbles on Ebay mentioned in conjunction with calibration.
Maybe you could check that out?

Mike

 

[Robert Baer]

Among the stuff in my father-in-law's basement I found a '1962 "Radiological
Survey Meter" which the manual says is only sensitive to gamma radiation.
"It is designed to be used by radiological Civil Defense personnel
in determining radioactive contamination levels that may result from an
enemy attack or other nuclear disasters."

It's claimed sensitivity runs from around 0.2 to 500 "roentgens per hour".
After changing the battery -- astoundingly for that era it's a single
pentode hybrid vacuum tube & single transistor circuit that runs on a
single D-cell -- it passed it's built in self-check which, according to the
schematic, just assures that the electronic circuitry is working close to
its design point. Since I'm not in a university and don't have any "radium
or Cobalt 60" laying around the house (AFAIK), I'm stumped as to finding a
method of determining if this thing still works. I'd appreciate suggestions
for either a Q&D function-test or a real calibration with a safe source of
around 4 r/hr of gamma radiation.

TIA
Norm

Your best bet would seem to go to a university "nearby" after calling
to be sure they have sources for the sensitivity check.
As long as the GM tube is still OK, the instrument should be fairly
close.
This could be considered a type of collectors item; keep it!

 

[Robert Baer]

Among the stuff in my father-in-law's basement I found a '1962 "Radiological
Survey Meter" which the manual says is only sensitive to gamma radiation.
"It is designed to be used by radiological Civil Defense personnel
in determining radioactive contamination levels that may result from an
enemy attack or other nuclear disasters."

It's claimed sensitivity runs from around 0.2 to 500 "roentgens per hour".
After changing the battery -- astoundingly for that era it's a single
pentode hybrid vacuum tube & single transistor circuit that runs on a
single D-cell -- it passed it's built in self-check which, according to the
schematic, just assures that the electronic circuitry is working close to
its design point. Since I'm not in a university and don't have any "radium
or Cobalt 60" laying around the house (AFAIK), I'm stumped as to finding a
method of determining if this thing still works. I'd appreciate suggestions
for either a Q&D function-test or a real calibration with a safe source of
around 4 r/hr of gamma radiation.

TIA
Norm

Your best bet would seem to go to a university "nearby" after calling
to be sure they have sources for the sensitivity check.
As long as the GM tube is still OK, the instrument should be fairly
close.
This could be considered a type of collectors item; keep it!

 

[Liui Ganishiapu]

You can buy some items from ebay to test with. If you are getting a click or
two per min, it is picking up background radiation, which means it is
working good. Many meters back then were for post necular war, which means
they only regester very high levels of radiation, which you don't want to be
around anyway. Do you have a make and model # on it?

 

[Jon Elson]

Among the stuff in my father-in-law's basement I found a '1962 "Radiological
Survey Meter" which the manual says is only sensitive to gamma radiation.
"It is designed to be used by radiological Civil Defense personnel
in determining radioactive contamination levels that may result from an
enemy attack or other nuclear disasters."

It's claimed sensitivity runs from around 0.2 to 500 "roentgens per hour".
After changing the battery -- astoundingly for that era it's a single
pentode hybrid vacuum tube & single transistor circuit that runs on a
single D-cell -- it passed it's built in self-check which, according to the
schematic, just assures that the electronic circuitry is working close to
its design point. Since I'm not in a university and don't have any "radium
or Cobalt 60" laying around the house (AFAIK), I'm stumped as to finding a
method of determining if this thing still works. I'd appreciate suggestions
for either a Q&D function-test or a real calibration with a safe source of
around 4 r/hr of gamma radiation.

I'm guessing, from the description, that this is an ionization chamber,
not a
Geiger-Muller tube detector. There were dinner plates made in the 70's with
a VERY bright orange glaze made from Uranium. They were recalled, but
some people have kept them around. If you can find one of these at a flea
market, even a small chip will easily trigger a Geiger counter. A whole
plate should be able to give a reading on even a poor ionization chamber
detector.

Another common radiation source is a gas mantle, as in yard lamps and
Coleman lanterns. They have thorium in them. Thoriated Tungsten TIG
electrodes are also radioactive. (I can't remember if this is a Gamma
source or not, though.)

Even household bricks are weak radiation sources, but I suspect way too
weak for such a detector to pick up.

The Geiger-tube detectors usually have a small label on the side marked
"test detector here", which has a suitable source for checking the detector.
The ion chamber units are usually one-piece, so a test source would be
hard to provide, but you might look around and see if there is such a
label present.

Jon

 

[[email protected]]

Among the stuff in my father-in-law's basement I found a '1962 "Radiological
Survey Meter" which the manual says is only sensitive to gamma radiation.
"It is designed to be used by radiological Civil Defense personnel
in determining radioactive contamination levels that may result from an
enemy attack or other nuclear disasters."

It's claimed sensitivity runs from around 0.2 to 500 "roentgens per hour".
After changing the battery -- astoundingly for that era it's a single
pentode hybrid vacuum tube & single transistor circuit that runs on a
single D-cell -- it passed it's built in self-check which, according to the
schematic, just assures that the electronic circuitry is working close to
its design point. Since I'm not in a university and don't have any "radium
or Cobalt 60" laying around the house (AFAIK), I'm stumped as to finding a
method of determining if this thing still works. I'd appreciate suggestions
for either a Q&D function-test or a real calibration with a safe source of
around 4 r/hr of gamma radiation.

TIA
Norm

Your meter is not the low level training type. It is the actual
usage kind.

Calibration is expensive. A few hundred dollars at a commercial laboratory
I would guess.

If you live near a nuclar power plant you could run after
a radioactive waste hauling truck and try to get it calibrated to the
trucks postings???? Stay cool looking when you do this though, beccause
you just might be mistaken for a bad guy.

Anyways, nothing in common use in the consumer realm is radioactive
enough to give an indication. You are just out of luck.

 

[ping]

Among the stuff in my father-in-law's basement I found a '1962 "Radiological
Survey Meter" which the manual says is only sensitive to gamma radiation.
"It is designed to be used by radiological Civil Defense personnel
in determining radioactive contamination levels that may result from an
enemy attack or other nuclear disasters."

It's claimed sensitivity runs from around 0.2 to 500 "roentgens per hour".
After changing the battery -- astoundingly for that era it's a single
pentode hybrid vacuum tube & single transistor circuit that runs on a
single D-cell -- it passed it's built in self-check which, according to the
schematic, just assures that the electronic circuitry is working close to
its design point. Since I'm not in a university and don't have any "radium
or Cobalt 60" laying around the house (AFAIK), I'm stumped as to finding a
method of determining if this thing still works. I'd appreciate suggestions
for either a Q&D function-test or a real calibration with a safe source of
around 4 r/hr of gamma radiation.

TIA
Norm

The radioactive substance in smoke detectors is Am-241, but it is
tiny. I am not sure if your detector would even be able to detect
that. But the most important thing for calibration is having a know
quantity of disinigrations per sec or, 1 bequerel.

You also mentioned the Roentgen.

The Roentgen (R) is a unit used to measure a quantity called exposure.
This can only be used to describe an amount of gamma and X-rays, and
only in air. One roentgen is equal to depositing in dry air enough
energy to cause 2.58E-4 coulombs per kg. It is a measure of the
ionizations of the molecules in a mass of air. The main advantage of
this unit is that it is easy to measure directly, but it is limited
because it is only for deposition in air, and only for gamma and x
rays.

dan

 

[Bart Wessel]

I'd appreciate suggestions
for either a Q&D function-test or a real calibration with a safe source of
around 4 r/hr of gamma radiation.

No need to buy your own radioactive source.
Pay your local fire department a friendly visit. They have meters and
a source to check them. If they are not out on a job, they'll probably
welcome the distraction from daily duties and take the oportunity to
restudy the subject.
Well, that's what happened to me when I visited the guys here... Had a
very interesting lecture on the subject from the Chief! And yes, my
meter worked almost perfectly.

BartW.
Bart.

There may be a 'NOSPAM.' (mind the dot!) in front of my E-mail address.
It is there to fool machines, not people. Please remove it when you want to reply to me personally.

 

[Norm Dresner]

You can buy some items from ebay to test with. If you are getting a click or
two per min, it is picking up background radiation, which means it is
working good. Many meters back then were for post necular war, which means
they only regester very high levels of radiation, which you don't want to be
around anyway. Do you have a make and model # on it?

It's a Victoreen Model 1A [also called a CD V-715] "designed to be used by
radiological Civil Defense personnel in determining radioactive
contamination levels that may result from an enemy attack or other nulear
disasters."

The range of sensitivity is roughly .03 to 500 roentgens per hour and is
supposed to be sensitive to only gamma radiation. It contains a
"hermetically sealed ionization chamber" and the case is fairly thick metal
so I'd believe that it would stop [not to energetic] alpha and beta
radiation.

Exactly what did you have in mind that I could find on eBay that would be a
decent gamma emitter?

Norm

 

[Jim Adney]

I'm guessing, from the description, that this is an ionization chamber,
not a Geiger-Muller tube detector.

What's the difference between the two? I thought the G-M tube WAS an
ionization chamber.

-

 

[John McMillan]

It's a Victoreen Model 1A [also called a CD V-715] "designed to be used by
radiological Civil Defense personnel in determining radioactive
contamination levels that may result from an enemy attack or other nulear
disasters."

The range of sensitivity is roughly .03 to 500 roentgens per hour and is
supposed to be sensitive to only gamma radiation. It contains a
"hermetically sealed ionization chamber" and the case is fairly thick metal
so I'd believe that it would stop [not to energetic] alpha and beta
radiation.

If you search on Google you'll find pictures and details of that instrument.
As you say its based on an ionization chamber. I'm guessing that the
electronics was some sort of electrometer circuit - it converts the
ionization in the chamber to a DC current displayed on the meter.
So, unlike the pulse processing used with a geiger tube, there
won't be any clicks to listen for.

Exactly what did you have in mind that I could find on eBay that would be a
decent gamma emitter?

Your best choices for radioactive material to demonstrate that the
unit is working are gas lamp mantles (Welsbach mantles) containing
Thorium and old luminous watches (or luminous instrument dials)
containing radium. Then there are geological samples like pitchblende
(uranium) and monazite (thorium). There are ceramics around with
uranium in the glaze and thoria crucibles have been used for high
temperature stuff. Another approach is to take a domestic smoke
detector and extract the source from it. Its normally about
40 kilobecquerels of Americium-241 which besides being an alpha
emitter gives 60keV gammas. When handling this (or any other)
source, treat it with respect and above all avoid ingesting the
material.
My last suggestion for an easily available source is
a few hundred grams of "low-sodium" salt - which is mostly
potassium chloride. All potassium salts contain Potassium-40
which is a gamma emitter (1.4MeV). With a geiger, 200g "low sodium"
close to the tube doubles the background rate. However in your
case I suspect that the ionization chamber will not be sensitive enough to
detect it.
Having demonstrated that the unit works, you might still want
to calibrate it. I can't imagine that it was ever particularly
accurate - more a go/no-go device. Accurate calibration really
will require the resources of a decent radiological lab and this
will take time and effort.

regards

John McMillan

 

[Jon Elson]

What's the difference between the two? I thought the G-M tube WAS an
ionization chamber.

Well, yes, ionization works in both. But, in a G-M tube, the high
voltage gradient causes an avalanche that drains the charge stored
on the capacitance of the tube and wiring until the discharge
quenches, and the circuit resets. This causes a very large voltage
spike which is easily detected, and you "count" the pulses to
get dose rate. (Most G-M counters use some kind of gated integrator
to convert the pulses to an analog voltage to be displayed on
a DeArsonval meter.)

An ionization chamber radiation meter does NOT work in the avalanche
mode, but uses a very sensitive current sensing circuit (usually
using Victoreen electrometer tubes) to sense the current flowing
across a large gas-filled chamber and polarized with a very LOW
electric field. Instead of fields like 900 V/cm in the G-M tube,
you'd see 20 V/10 cm in an ionization chamber. The ions drift slowly
across the chamber, and picoampere currents flow. The design of
the chamber and window often allow much lower particle energies to
be detected with an ion chamber. Also, extremely high dose rates
which would saturate a GM tube can be accurately measured with
an ion chamber. Of course, if you ever see these sorts of rates,
you'd better run like hell!

Jon

 

[Norm Dresner]

The Roentgen (R) is a unit used to measure a quantity called exposure.
This can only be used to describe an amount of gamma and X-rays, and
only in air. One roentgen is equal to depositing in dry air enough
energy to cause 2.58E-4 coulombs per kg. It is a measure of the
ionizations of the molecules in a mass of air. The main advantage of
this unit is that it is easy to measure directly, but it is limited
because it is only for deposition in air, and only for gamma and x
rays.

What's the probability that X-Rays from a dentist's equipment would possess
enough energy to register in the detector?

Norm

 

[Norm Dresner]

It's a Victoreen Model 1A [also called a CD V-715] "designed to be used by
radiological Civil Defense personnel in determining radioactive
contamination levels that may result from an enemy attack or other nulear
disasters."

The range of sensitivity is roughly .03 to 500 roentgens per hour and is
supposed to be sensitive to only gamma radiation. It contains a
"hermetically sealed ionization chamber" and the case is fairly thick metal
so I'd believe that it would stop [not to energetic] alpha and beta
radiation.

If you search on Google you'll find pictures and details of that instrument.
As you say its based on an ionization chamber. I'm guessing that the
electronics was some sort of electrometer circuit - it converts the
ionization in the chamber to a DC current displayed on the meter.
So, unlike the pulse processing used with a geiger tube, there
won't be any clicks to listen for.

Yes. The circuit contains exactly one transistor used as an oscillator to
drive the primary side of a transformer to get the voltages needed to run
the ionization chamber and the Ion Current Detector Tube (VX86 manufactured
by Victoreen) which contains a cathode, an anode, and two grids. Based on
the resistors in the circuit (they range from 220 Megohms up to 220
gigohms), we're talking about picoamperes of ionization current being
detected. The circuit itself is a marvel of economy. with just the two
active elemetns and three diodes along with the resistors and capacitors.
I'm going to try to find a luminous watch first and, failing that, use one
of the two smoke detectors we have.

Thanks for the suggestions
Norm

 

[Bilge]

Norm Dresner:

What's the probability that X-Rays from a dentist's equipment would possess
enough energy to register in the detector?

Depends upon what the counter was originally designed to count. If
the window is thin enough, x-rays should be fine, unless you want to
check the calibration rather than just find out if it detects gammas.
The best way to find out is try it. If it doesn't respond, then either
it doesn't or the window is too thick, in which case, you'll have to
find a higher energy source. If you have a smoke detector which
uses 241Am, that will also provide a source low energy (approx 50 keV)
X-rays. (Your counter won't see any of the alpha's from the 241Am).

You might also try to find a physician or veterinarian who does
radiation therapy. These days, even veterinarians have linacs and
use radionuclides for treating cancers in animals. Decay energies
for those isotopes will be nominally in the MeV range. If your counter
doesn't see those, it doesn't work.