Geiger-Mueller counting

Counter, Geiger-Mueller (GM counter)—Highly sensitive, gas-filled radiation-measuring device to detect (count) individual photons or particulate radiation. 

The astatine vapor is invisible, but since it is radioactive we can count its nuclear disintegrations with a Geiger-Mueller counter. 

Hans Geiger worked in Ernest Rutherford s laboratory manually and meticulously counting a-particle scintillations for the famous experiments that led to the discovery of the nucleus. Because of this work, he developed an a-particle detector. After World War I, Geiger developed the modern Geiger-Mueller counter and worked until his death to increase its speed and sensitivity. 

Material around the source and detector, notably the detector housing, cause scattering into the detector. The opportunity for scattering into the detector increases when the source is more distant. This scattering adds a few percent to the count rate for end-window Geiger-Mueller (G-M) detectors when the sample is 2 cm or more distant (Zumwalt 1950), but little for gas-flow proportional counters with the sample only about 0.3 cm from a relatively large window. Scattering, attenuation. 

Zumwalt, L. R. 1950. Atomic Energy Commission Report AECU-567. Absolute beta counting using end-window Geiger-Mueller counters and experimental data on beta-particle scattering effects. Washington, DC AEC. 

The material is placed in an evacuated bell jar Fig. 28.2) and evaporated onto polystyrene discs, 15/16 in. in di. The discs are removed from the bell jar and counted with the s, Geiger-Mueller system. The counting rate at this time is extra] back to the initial counting period. The ratio of the counting rat termines the ratio of the mass of the material on the polystyrem the original mass. 

A Geiger-Mueller end-window counter (see Fig. 28.3) is used for counting the P beta particles. There are five shelf positions at varying distances from the tube. The shelf positions are calibrated... 

The gold foil is counted with a calibrated Geiger-Mueller counter which has been calibrated previously by use of a standard pile of known flux. From this measurement, the thermal flux in which the phosphorus was irradiated can be determined. The phosphorus pellet is then counted with the end-window counter. As previously stated, the range of the beta particle determines the active weight which is counted. The counting rate is given by... 

The manganese foil discs and the sodium pellets do not require an absolute measurement of activity, since only their cadmium ratios are necessary for the experiment. The manganese will be counted with an end-window Geiger-Mueller counter, and the sodium with the Nal scintillation counter. 

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