Detectors analog-counting

FIGURE 21.4 The detector electronics must be able to switch fast enough to detect isotope ratios that require both pulse and analog counting modes (data copyright 2003-2007, all rights reserved, PerkinElmer Inc.). 

The two detector modes should be calibrated to generate the conversion factor from analog counts to equivalent pulse counts. 

SPC techniques offer the advantage of low noise detection, providing / -values of 1-2 times lower than in analog detection. Although this can in principle result in four times faster acquisition speed this gain in speed is not realized in practice. In SPC, the comparatively high dead-times of detectors and electronics limits the acquisition speed. SPC system should be operated at count rates below the inverse of the dead-time of the system (electronics... 

Electron multipliers can also be operated in analog mode as current detectors. In this mode, they have a lower gain and measure higher signals than in pulse-counting mode. This... 

Figure 10.31 shows what is now a common counting system for y-y coincidence measurements using a NaI(Tl) detector and a Ge(Li) detector. The initials ADC stand for analog-to-digital converter (see Sec. 10.12). 

There are two ways to interpret the detector signals shown in Fig. 1.1. The detector signal can be considered as a waveform superimposed over the shot noise of the photons, or as a random sequence of pulses originating from individual photons. The first leads to analog signal recording, the second to photon counting. 

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