Introduction

All radiation detectors used in diffractometry function in a basically similar fashion: the detection of an individual incident X–ray quantum or neutron results in the collection of a certain quantity of electrical charge at the input terminal of the detecting circuitry. No matter what the actual detector may be, this resultant charge may be dealt with in one of two ways. Either the charge which corresponds to the arrival of a given number of pulses per unit time is integrated and the resultant current is taken as a measure of the incident intensity, or the individual pulses of charge are counted, if necessary after amplification and shaping.

The first method, that of current measurement, is used only with X–ray ionization chambers which are rarely employed today. All other X–ray and neutron detectors are ‘counters’ which produce discrete pulses. These detectors have the important feature that the result of an intensity measurement is given directly in digital form as the number of incident quanta or neutrons in a given time interval: such digital data are thus already in a suitable form for further processing.

It is easy to specify the requirements to be met by an ideal detector for use in diffraction studies.