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The Microanalysis System

What makes a Good Detector?

The Pulse Processor

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Role of the pulse processor
Analog pulse shaping
Time variant shaping
Digital pulse shaping
Fixed process time
Adaptive pulse shaping
Resolution & count rate
Pulse pile-up protection
Comparing different pulse processors
Summary

The pulse processor

Processors with fixed process time

The longer the process time (T_P), the lower the noise. If noise is minimized, the resolution of the peak displayed in the spectrum is improved (see Fig. 15), and it becomes easier to separate or resolve, from another peak that is close in energy (Fig. 16). However, there is a trade-off between the process time that is used, and the speed at which data can be measured. The longer the process time, the more time is spent measuring each X-ray, and the fewer events that can be measured. The longest process time used by a processor gives the best resolution possible while the shortest process time gives the maximum throughput into the spectrum, but with the worst resolution (Fig. 16).

Productivity depends on the rate of counts measured, called the acquisition rate, rather than the input rate (into the detector). As the input rate increases so will the acquisition rate, but an increasing number of events are rejected because they arrive in a shorter time period than T_P (Fig. 15). If input rates increase sufficiently, the proportion rejected will exceed the increase in measured events and the acquisition rate will start to decrease with further increases in input rate (Fig. 17).

Therefore for each process time there is a maximum acquisition rate (Fig. 17) which corresponds to the maximum speed possible for a chosen resolution. The maximum acquisition rate for each process time is characteristic of the pulse processor used. By determining, for each processor setting, the maximum acquisition rate and the resolution at this rate, the productivity and performance of a processor can be evaluated.

In a processor where the process time is fixed, the trade off between resolution and acquisition rate can be controlled and the resolution accurately defined.

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