Geiger-Mueller (Wiki: Tube,
Counter)
These are the most common "Geiger
Counter" sensors. They are biased with enough voltage so
that when an atomic particle gets into the gas it causes an
avalanche. The size of the output pulse is the same no
matter what the energy of the input particle. Although
it's possible to turn down the voltage so that the output pulse
has a relation to the input particle energy, the operation is
then no longer called Geiger Mueller.
There is a plateau in the count rate vs. applied voltage plot for a G-M tube and it should be operated on the plateau, not above or below. The recomended voltage for most tubes is in the 500 to 900 volt area.
After the particle leaves the tube there is a recovery time. If another particle enters the tube before the recovery time has passed the tube will conduct continuously. This is bad because most Geiger counters will show zero when in fact they should be showing full scale.
The common G-M tube is a metallic cylinder with a wire insulated in the center. One end typically has a mica window to allow alpha particles to enter. But the end area is much smaller than the active area of a pancake type G-M tube. Pancake G-M tubes are much more sensitive to alpha as well as beta and gamma rays than the cylindrical type tubes.
The end of a "hot dog" type G-M tube or the face of a "pancake" tube typically has a thin mica window. Ideally for the detection of alpha particles there would be no window, but then the gas in the tube would except. The density of the window puts a limit on the energy level of the alpha particles that can get into the tube (typically around 3 Mev).
Google "Geiger Mueller"
The sensivity of a G-M type tube can be greatly increased by adding more electrodes.
2397071 Radiation Detector, Gerhard Herzog (Texaco - oil wells) - multiple cathode disks and multiple anode wires
2397072 Radiation Detector - multiple cathode disks and multiple anode wires
2397073 Radiation Detector - 5 to 10 times more sensitive than G-M tube, uses more electrodes, but has some volumes where the field is zero, hence there's a better way
2397074 Radiation Detector - very rugged
2397075 Radiation Detector - minimizes anode to cathode leakage (noise)
2873399 Radiation Detector - has no zero field volumes so is somewhat more sensitive than 5 to 10 times a G-M tube
There is a plateau in the count rate vs. applied voltage plot for a G-M tube and it should be operated on the plateau, not above or below. The recomended voltage for most tubes is in the 500 to 900 volt area.
After the particle leaves the tube there is a recovery time. If another particle enters the tube before the recovery time has passed the tube will conduct continuously. This is bad because most Geiger counters will show zero when in fact they should be showing full scale.
The common G-M tube is a metallic cylinder with a wire insulated in the center. One end typically has a mica window to allow alpha particles to enter. But the end area is much smaller than the active area of a pancake type G-M tube. Pancake G-M tubes are much more sensitive to alpha as well as beta and gamma rays than the cylindrical type tubes.
The end of a "hot dog" type G-M tube or the face of a "pancake" tube typically has a thin mica window. Ideally for the detection of alpha particles there would be no window, but then the gas in the tube would except. The density of the window puts a limit on the energy level of the alpha particles that can get into the tube (typically around 3 Mev).
Google "Geiger Mueller"
The sensivity of a G-M type tube can be greatly increased by adding more electrodes.
2397071 Radiation Detector, Gerhard Herzog (Texaco - oil wells) - multiple cathode disks and multiple anode wires
2397072 Radiation Detector - multiple cathode disks and multiple anode wires
2397073 Radiation Detector - 5 to 10 times more sensitive than G-M tube, uses more electrodes, but has some volumes where the field is zero, hence there's a better way
2397074 Radiation Detector - very rugged
2397075 Radiation Detector - minimizes anode to cathode leakage (noise)
2873399 Radiation Detector - has no zero field volumes so is somewhat more sensitive than 5 to 10 times a G-M tube
Calls:
2599352 Radiation Detector - greater cathode area by adding fins - more sensitive
2649554 Radiation Indicator, Anton - (beta & gamma dosemeter)
2699513 Radiation Detector -multiple anode wires in addition to increased cathode area
2599352 Radiation Detector - greater cathode area by adding fins - more sensitive
2649554 Radiation Indicator, Anton - (beta & gamma dosemeter)
2699513 Radiation Detector -multiple anode wires in addition to increased cathode area
Scintillator (Wiki)
Some crystal or plastic that
generates a photon of light when hit by a particle is coupled
with a photo multiplier tube and both enclosed in a light tight
package. The output pulse is proportional to the energy of
the input particle.
Ionization Chamber (Wiki)
An insulating chamber with some
gas the ionizes under the influence of strong radiation.
Many of the surplus civil defense survey meters (often
erroneously called geiger counters) use this type of detector.
Spinthariscopes (Wiki)
This is a hand held magnifier
focused on a screen made of Silver activated Zinc Sulfide and
with an alpha emitter source like Po-210 Polonium (Anti-Static
Brush) or AM-241 (Smoke Detector). With a night adapted
eye you can see the scintillation. These show up on eBay,
new from United Nuclear, old from antique instrument dealers.
Lone Ranger Atom Bomb Ring
The first thing I did was check it with the Bicron Surveyor
50 with LND pancake probe and detected no radiation
above background.
 |
 |
ORAU Museum of Radiation and Radioactivity: Lone Ranger Atom Bomb Ring Spinthariscope (1947-Early 1950s) - In a reply this said this ring has decayed to the point where the sparkles are no longer visible. Hence my looking for a working Spinthariscope. All the older models have long since lost their radiation since the alpha sources have a short half life.
United Nuclear Super Spinthariscope
New as of January 2023 so should have some Thorium (Wiki) life
left in it.
It's built into a 1-1/2" PVC end cap. The "Super" version
has the Thorium mounted on the end of a threaded rod so that its
distance to the ZnS screen and be adjusted. There's also a
built-in magnifier with an optical diameter of 1 inch.
The focal length of the lens is about 37mm to the edge of the
flange facing the screen.
The ZnS screen is about 33mm down from the edge of the 1-1/2"
fitting.
So nominal focus would be with a 4 mm gap between the magnifier
and the housing.
The fine threads on the magnifier and on the mating part are
plastic so a great deal of care is needed to engage the threads
properly if you remove the magnifier lens.
Fig 1 |
Fig 2 |
Other Detectors
There are many other ways of
detecting atomic radiation. One of the first was the use
of photograph film.
Dose Meters (Wiki)
While Geiger counters measure the
rate (i.e. counts per minute) a dose meter adds up the counts
giving a total exposure. These are usually in the form of
badges that may have photographic film or an electronic
integrator or pen shaped electrometer.
X-Ray (Wiki)
One way to detect X-Rays is to use
a Scintillator coupled to a photomultiplier tube in a light
tight manner. This was the method used on first generation
CAT scanners. The problem is that you can only have a
small number of these around the circumference of a circle and
so the spacial resolution is low. GE developed X-Ray
sensors using Xenon gas that can have many more sensors in the
same space where there were only a few photomultiplier
types. As of 2008 this is a hot bed of activity since CAT
is the preferred method of imaging many things in the human body
(i.e. is preferred over MRI which is good for other things).
4031396 X-ray Detector, GE - multiple anode wires in a curved chamber for CAT scanner
4707607 High Resolution X-Ray Detector, GE - an even higher resolution detector using a flow of Xenon gas through the curved chamber for CAT scanner
7355181 Radiological imaging apparatus and radiological imaging method and radiological imaging support method, Hitachi - combines CAT and PET images
4031396 X-ray Detector, GE - multiple anode wires in a curved chamber for CAT scanner
4707607 High Resolution X-Ray Detector, GE - an even higher resolution detector using a flow of Xenon gas through the curved chamber for CAT scanner
7355181 Radiological imaging apparatus and radiological imaging method and radiological imaging support method, Hitachi - combines CAT and PET images
8126109
X-Ray CT Apparatus and an Image Controlling Method Thereof,
Toshiba - An X-ray CT apparatus and image controlling method
thereof that achieves a higher time resolution tomography image
on a region of interest (ROI) of an object while reducing a
total amount of X-ray irradiation exposure.
