G-M detector

DESCRIBE the operation of a Geiger-Muller (G-M) detector to include ... 

The voltage of a Geiger-Miiller (G-M) detector is set so that any incident radiation produces the same number of electrons. 

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. 

The dead time is long in a G-M counter because of its large and wide pulses, but short in a proportional counter. For a G-M detector with a dead time of 0.5 p.s, a measured count rate of 200 c/s implies a loss of 11% according to Eq. (8.6). In contrast, a proportional counter with a dead time of 5 p,s has a loss of only 0.1% at the same measured count rate. 

The reverse— gamma-ray background in beta-particle detectors—also occurs due to electron-producing interactions of gamma rays in the walls of the gas-filled proportional and G-M detectors. The magnitude of the detection efficiency for energetic gamma rays, i.e., above 0.1 MeV, typically is about 1% of that for beta particles (Knoll 1989). 

The G-M counter is a simple and relatively inexpensive gas-filled tube with a count-rate meter an amplifier may also be present. The G-M detector counts alpha particles, beta particles, and gamma rays with a very thin window, counts beta particles and gamma rays with a thicker window, and counts gamma rays only with a thick shield. Alpha and beta particles interact in the gas gamma rays interact mostly in the walls, from which electrons enter the gas. The intrinsic efficiency for counting gamma rays relative to beta particles depends on the amount and type of solids surrounding the detection gas. 

Screening measurements of incident response samples begin as soon as possible after sample receipt and logging. A necessary first step is prescreening to prevent a sample from being taken to a laboratory if its radionuclide content is unsuitably high for the usual controls of personnel radiation exposure and contamination of the analyst, the laboratory, and radiation detectors. External radiation is measured with conventional low-level radiation monitors that include the G-M detector and... 

Using Microsoft Excel or similar, plot the count rate, R, against the voltage, V, and determine the operating voltage, Vq, of the G.M. detector. 

Why is it a good idea to periodically check the high voltage (HV) plateau for G.M. detector Make the following conversions ... 

The absorption curves of the U"-radiation from the precipitates for the samples and the standards were measured by interposing aluminium discs with increasing thickness between the precipitate and the G-M detector. The curves for the sample and the standard were parallel, indicating that in both cases a radionuclide with the same iJ"-energy was detected. 

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