Special kinds of diffractometry

Display. The contents of the MCA memory (total counts in each channel) may be displayed visually as counts vs. channel number (= counts vs. x-ray energy) on a TV screen or by an X-Y plotter, or they may be recorded on printed tape, punched tape, or magnetic tape. 

Applications of the MCA to specific problems are given in Chap. 15 and in the next section. 

The ability of the MCA to sort out signals of various magnitudes has permitted the development of new kinds of diffractometers, radically different from the conventional, moving-counter instrument to which this chapter is mainly devoted. 

It is now appropriate to write the Bragg law in terms of quantum energy E rather than wavelength X  

At constant 0, measurement of E will give the spacing d of each set of planes, and their indices (hki) are found by the methods of Chap. 10. The experimental arrangement and an example of the results obtained, from a plot of the contents of the various channels of the MCA, are shown in Fig. 7-23. The specimen was a sheet of polycrystalline platinum. 

---

Circuits (1) and (2) may be used with ordinary diffractometers to increase the peak/background ratio of diffraction lines. They are by no means necessary quite adequate diffraction patterns can be obtained from a wide variety of specimens with no other discriminator than a Kp filter. Circuit (3) is required only in x-ray spectroscopy (Chap. 15), in a very special kind of diffractometry (Sec. 7-10), and with a position-sensitive proportional counter. Any one of these circuits is more effective, the better the resolution of the counter with which it operates. 

---