Counters Geiger

Geiger counter A device used to detect and measure amounts of radioactivity. 

With the help of Geiger counter the p- and y-radiations are registered. 

There are many types of electronic detector. The original fomi of electronic detector was the Geiger counter, but it was replaced many years ago by the proportional counter, which allows selection of radiation of a particular type or energy. Proportional counters for x-rays are filled witii a gas such as xenon, and those for... 

Geiger counter (p. 643) half-life (p. 643) isotope dilution (p. 646)... 

Geiger counter an instrument for counting radioactive particles based on their ability to ionize an inert gas such as Ar. (p. 643)... 

Geiger counter Geiger-Mueller probe Geiger-Muller counters GEKKO XII Gelatin... 

The methods for detection and quantitation of radiolabeled tracers are deterrnined by the type of emission, ie, y-, or x-rays, the tracer affords the energy of the emission and the efficiency of the system by which it is measured. Detection of radioactivity can be achieved in all cases using the Geiger counter. However, in the case of the radionucHdes that emit low energy betas such as H, large amounts of isotopes are required for detection and accurate quantitation of a signal. This is in most cases undesirable and impractical. Thus, more sensitive and reproducible methods of detection and quantitation have been developed. 

A Geiger counter counts 0.070% of all particles emitted by a sample. What is the activity that registers 19.4 X 103 counts in one minute ... 

Fluorine-18 has a decay constant of 6.31 X 10-3 min-1. How many counts will one get on a Geiger counter in one minute from 1.00 mg of fluorine-18 Assume the sensitivity of the counter is such that it intercepts 0.50% of the emitted radiation. 

Fig. 2-2. Schematic diagram of Geiger-counter tube. A typical end-window Geiger tube. The nature of the window will depend on the kind of rays to be detected. This tube will operate under the conditions of Fig. 2-3.

At present, the Geiger counter is the most popular x-ray detector in analytical chemistry. Although it is yielding ground to the proportional counter and the scintillation counter, it will be remembered for having greatly accelerated the use of x-ray emission spectrography in analytical chemistry. 

The enormous value of A means that Geiger counters respond satisfactorily to x-rays of long wavelengths. The counters are easy to use. They are now relatively stable and trouble-free—surprisingly so in view of the complexities described below. Frequent recalibration is desirable, however, in highly precise work. 

Because the Geiger counter produces pulses independent in size of x-ray wavelength, it is the best detector for the method of counting that employs a capacitor to accumulate the individual counts (2.3, 2.10). 

Intensity measurements are simplified when a detector always gives one electrical pulse for each x-ray quantum absorbed the detector remains linear so long as this is true. For low intensities, when the rates of incidence upon the detector are low, the Geiger counter fulfills this condition. As this rate increases above (about) 500 counts per second, the number of pulses per second decreases progressively below the number of quanta absorbed per second. This decrease occurs even with electronic circuits that can handle higher counting rates without appreciable losses. 

The cause of this difficulty therefore resides within the counter itself. The difficulty is described by saying that the Geiger counter has a dead time, by which is meant the time interval after a pulse during which the counter cannot respond to a later pulse. This interval, which is usually well below 0.5 millisecond, limits the useful maximum counting rate of the detector. The cause of the dead time is the slowness with which the positive-ion space charge (2.5) leaves the central wire under the influence of the electric field. This reduction in observed counting rate is known as the coincidence loss. 

The tube of Figure 2-2 can be operated as an ionization chamber, as a proportional counter, or as a Geiger counter. The tube output differs radically from one case to another. Because of these differences, the electronic circuitry associated with the tube must also be different for each case if the pulses from the tube are to be reliably selected and counted. In particular, the circuitry will have to differ in characteristics such as stability, amount of amplification, and time of response. In all cases, linear amplification (amplifier output always proportional to tube output) is desirable. 

Recent papers from the Philips Laboratories37 40 contain thorough discussions of the Geiger counter, the proportional counter, and the scintillation counter, and significant performance data for all three, the emphasis being placed throughout upon x-ray applications. The detection system employed by Parrish and Kohler was particularly noteworthy in that it could conveniently accommodate any one of four detectors. ... 

Geiger counter for routine diffraction and other work involving low counting rates. 

When Fe-55 became available, Hughes and Wilezewski4 found it possible to improve further the valuable method just described by using this radioactive isotope as an x-ray source. Four millicuries of iron, in the form of a button that initially had 15(107) disintegrations per second, was mounted as shown in Figure 5-2, the Geiger counter being movable... 

Fig. 5—6. Geiger-counter output currents recorded by Dow automatic x-ray absorption spectrometer. Superposed records on left are x-ray absorptiometric curves for iso-octane and a solution containing ethylene dibromide, whereas traces at right illustrate recording of transmitted intensities at fixed wavelengths. Apparent change in x-ray absorption of solvent in going through bromine absorption edge is result of marked slope of white radiation distribution curve at 0.9 A. 16 (Liebhafsky, Anal. Chem., 21, 17. Courtesy of Dow Chemical Company.)...

In 1950, Beeghly6 published results obtained by Method I on tin plate. Pie used a polychromatic beam from a copper-target tube to excite the K lines of iron in the substrate and measured the intensity of the radiant energy that passed the collimating slit to reach the Geiger counter that served as detector (Figure 6-1). A manganese filter in the... 

Fig. 7-12. The curved-crystal spectrometer of Adler and Axelrod, showing a polished ore specimen in position. (1) Microscope stage (2) polished ore sample (3) crystal support block (4) Geiger counter and scatter slits. (Courtesy of Adler and Ayelrod and the U. S. Geological Survey.)...

The reader will appreciate that Figure 9-1 does not illustrate the alternative method of collecting information (2.6, 2.7) in which the output of a Geiger counter is used to charge a capacitor. This method has been put to good use by the Applied Research Laboratories (9.8). 

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