Detectors ratemeters

Absorption or scattering of radioactive radiation is applied in industry for measurement of thickness or for material testing. For example, the production of paper, plastic or metal foils or sheets can be controlled continuously by passing these materials between an encapsulated radionuclide as the radiation source and a detector combined with a ratemeter, as shown in Fig. 20.2. After appropriate calibration, the ratemeter directly indicates the thickness. The radionuclide is chosen in such a way that the radiation emitted is eflFectively absorbed in the materials to be checked. Thus, the thickness of plastic foils is measured by use of f emitters, whereas Cs or other y emitters are used for measuring the thickness of metal sheets. 

Hence, the photographic film vaguely resembles a ratemeter because the intensity is extracted from the degree of darkening of the spots found on the film - the darker the spot, the higher the corresponding intensity because the larger number of photons have been absorbed by the spot on the film surface. The three most commonly utilized types of x-ray detectors today are gas proportional, scintillation, and solid-state detectors, all of which are true counters. 

Figure 4.18 Calibration of the detector and amplifier gain using the pulse height selector. The amplifier output pulse height spectra are shown at gains of (a) 50, (b) 100, and (c) 150. The ratemeter counting rate as a function of gain setting is shown in (d) for a 4-V integral discriminator threshold. (Reprinted by courtesy of EG G ORTEC.)...

Bicron Frisk-Tech Ratemeter (This instrument is also used in the Continuous Air Monitor and Stack Monitor Systems.) Indicates count rate only. Usually equipped with "pancake" GM detector, although other detectors can be used. Approximate cpm/mr/hr indicated on calibration tag. Used to check for contamination or activity of a sample or surface. NOT INTENDED FOR DOSE MEASUREMENT Has audible... 

Preamplifiers are used in nuclear channels in which the variable of interest is the rate of pulses occurring within the detector. Since they are installed in places with high radiation fields, their main purpose is to increase the pulse amplitude with a minimum of electronic components. Therefore, the output pulse of the preamplifier is not, suitable for count rate meters, and additional signal conditioning is necessary. Linear amplifiers provide the necessary means to discriminate the undesirable noise and to properly shape the pulses, making them compatible with counters, ratemeters and spectroscopy analyzers. Conventional solid state amplifiers are an essential part of reactor protection systems, NIM modules are preferred, but many research reactors I C systems have integrated nuclear channels. Both of them have shown to be reliable and safe. 

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