Multichannel analyzer pulse-height analysis

Fig. 15-1 X-ray fluorescence spectrometers. In this example, elements 1 and 2 in the sample emit characteristic wavelengths and k2- These wavelengths are separately measured by crystal diffraction in (a) or by pulse-height analysis in (b), where MCA = multichannel analyzer.

To measure an energy spectrum of a radioactive source means to record the pulse-height distribution produced by the particles emitted from the source, which is achieved with the use of an instrument called the multichannel analyzer (MCA). Multichannel analyzers are used in either of two different modes the pulse-height analysis (PHA) mode or the multichannel scaling (MCS) mode. 

Figure 4.22 The analysis of the shaping amplifier output pulse heights into the x-ray energy spectrum, (a) A multiple-trace oscilloscope picture of the pulse-shaping amplifier output for a spectrum containing Mn and Ag K x-rays, (b) The analyzed pulse height spectrum as viewed on the multichannel analyzer display. Each dot represents one channel in the analyzer memory. The channel numbers have been calibrated in terms of x-ray photon energy. (Reprinted by courtesy of EG G ORTEC.)...

The amount of data to be handled during this evaluation procedure requires the use of computers. At present, the multichannel analyzer not only carries out pulse height analysis but also does most of the data processing. The manufacturers of computer-based MCAs usually provide built-in or software programs for the different aforementioned steps. 

The acquisition of the spectral information from each single spark separately is now possible with advanced measurement systems, using integration in a small capacitor and rapid computer-controlled readout combined with storage in a multichannel analyzer. With the aid of statistical analysis, sparks with outlier signals can be rejected and the precision improved accordingly. Furthermore, pulse differential height analysis enables discrimination between a number of elements such... 

Excitation by high-energy electrons, radioactive particles or X-rays may be used. Analysis of the emitted X-rays using crystal analyzers is followed by detection using gas ionization detectors or scintillation counters. Nondispersive semiconductor detectors and multichannel pulse height analyzers are often used in conjunction with scanning electron microscopes. 

---