Ratemeter calibration

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. 

ISO. X and Gamma Reference Radiations for Calibrating Dosemeters and Dose Ratemeters. ISO 4037 (1979). 

The ions are detected using a channel electron multiplier (Valvo) and a combined counter/ratemeter registering unit (Ortec). The channel electron multiplier is operated at —3 kV. A linear emitter heating current (EHC) programmer is employed for the desorption of the samples. In all cases the EHC is raised at 0.19 mA/s from 0 to 100 mA (see Fig. 14). All measurements for the calibration curve of [Cs] (see Fig. 13) are made with one FD emitter starting from small sample amounts. 

These methods, apply as well to gases as to hquids, at high or low pressure. The techniques of measure of flow are immediate and are not thus useful for continuous measures. We apply them for the calibration of classic devices (ratemeters), with a 1 % precision, or in the studies of circuits with tapping. 

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.)...

Figure 35. Facilities utilized in a study of activity patterns of the meadow vole (Microtus pennsyl-vanicus) marked with a Ta wire, (a) Enclosure with detection unit. The probe is on the end of the boom, which rotates once each 6 min. (b) A log/linear ratemeter housed in an insulated box (cover removed for photograph). The stationary base contains the motor, the commutator, and a cam-operated microswitch, (c) Position and motion of the boom in the enclosure (a) the three positions used to calibrate each radioactive vole are X, Y, and Z. The records that result from a vole s being present in these three positions are shown at the right (A, B) from position X (C) from position Y (D) from position Z. (a-c) From Graham and Ambrose (1%7). (a, b) Photographs courtesy of F. C. Evans.

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... 

---