Pulse height

Figure Bl.10.7. Electron impact ionization coincidence experiment. The experiment consists of a source of incident electrons, a target gas sample and two electron detectors, one for the scattered electron, the other for the ejected electron. The detectors are coimected tlirough preamplifiers to the inputs (start and stop) of a time-to-amplitiide converter (TAC). The output of the TAC goes to a pulse-height-analyser (PHA) and then to a nuiltichaimel analyser (MCA) or computer.

A gamma-ray spectmm is produced nondispersively by pulse-height (multichannel) analysis using scintillation or semiconductor detectors. Resolving power, typically - 100 at 100 keV and - 700 at 2 MeV, is quite modest compared with that achievable in other spectral regions, but is sufficient to identify nucHdes unambiguously. 

Pulse-height selection.6 In some detectors, the mean height of the... 

Considerable confusion results because the terms pulse-height analysis, pulse-height discrimination, and pulse-height selection are sometimes used loosely or interchangeably. We shall follow The International Dictionary of Physics and Electronics, D. Van Nostrand Company, Inc., Princeton, N. J., 1950, pages 715 and 710, where the instruments for these techniques are described as follows ... 

Fig. 2-4. Mean pulse height versus quantum energy, to illustrate pulse-height selection of characteristic lines. Side window tube, 3-in. diameter 0.005-in. wire operating at 1275 v filled with argon plus 10% ethylene total pressure, 15 cm of mercury (proportional counter) gain, 3.5 X 104. (After Friedman, Birks, and Brooks, A STM Spec. Tech. Publ., No. 157, page 3. Copyright 1954. American Society for Testing Materials.)...

When a proportional counter is. used in conjunction with a pulse-height selector, the occurrence of an escape peak may vitiate the results. Assume that the counter filling contains argon, whose K edge is at 3.87 A, and suppose that the pulse-height selector is set to select an x-ray line 3f shorter wavelength the intensity of which is to be measured. This line will excite the K lines of argon. To the extent that these lines are... 

In the analysis of light elements where the wavelength differences to be resolved are large and it is difficult to get good crystals, pulse-height, selection has a promising future. 

Were these spreads not so likely to remain large, one could look forward to a replacement of crystals by pulse-height selectors as a means... 

There are ways of coping with these interferences. Pulse-height selection (2.13) is a direct method. As we shall see in Chapter 7, a particularly bad case, the determination of tungsten in aqueous solution with scattered target line and the identical line from the sample superimposed, could be handled successfully by properly correcting the background. 

Fig. 8-2. Background in the determination of aluminum in Alnico. Pulse-height selection facilitates the determination by reducing in importance the background and the lines (in 5th- and 3rd-order reflection) of the matrix elements, nickel and titanium. (After Noreleo Reptr., 3, 78.)...

Table 8-2 contains unpublished results fron the authors laboratory that illustrate the effectiveness of pulse-height selection in the determination of light elements. In the case of silicon, the background was due mainly to scattered x-rays. In the case of sulfur, multiplier phototube noise was also present. The counting interval was 10 seconds for Nt (total count) and for Nb (background). The excellent results for sulfur could not have been obtained had there not been careful and fortunate selection of the multiplier phototube. 

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