Radiation Detectors

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

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.

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.

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.

There are many other ways of detecting atomic radiation.

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 electronic integrators or pen shaped electrometers.

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 prefered method of imaging many things in the human body (i.e. is prefered 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

US 2007/0147576 A1 - 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.

Uses pancake G-M tube.  Ranges 0 - 0.5,  0 - 5 & 0 - 50 mR/hour.  9 volt battery.  Meter and when turned on clicks from speaker.

Military uses two hot dog type G-M types.  Started out in the early 1950s as an all tube instrument and has gone through many variations and now is mostly solid state and powered by 6 "D" batteries.

Geiger Counter .............................  250 / 374+ 
    Design .................................  D10 / 47 
    In nuclear reactions ...................  376 / 254 

Geiger Muller Tube .........................  313 / 93 
    Survey meter ...........................  250 / 374+ 
    With circuit ...........................  250 / 374+ 

 Calls:

249064 Receiver for Telephones, R M Lockwood, November 1, 1881, 181/167
454941 Phonograph Recorder or Reproducer, T A Edison, June 30, 1891, 181/162 ; 181/170
2159628 Telephone Transmitter, E G Danielson, May 23, 1939, 381/174 ; 181/167; 264/320; 425/DIG.56
2475603 Geiger Counter Structure, H Friedman, July 12, 1949, 313/93 ; 313/312; 313/622