Multichannel analyzer

A multichannel analyzer (MCA) is an instrument used in laboratory and field applications, so to analyze an input signal consisting of pulses.[1] MCAs are used extensively in digitizing various spectroscopy experiments, especially those related to nuclear physics, including various types of spectroscopy (alpha-, beta-, and gamma spectroscopy). MCAs are typically interfaced with via USB, RS-232 or Ethernet, but can use PCI also.

The output of an MCA used in PHA mode to analyze Cs-137

Operation
Pulse-Height Analyzer Principle: Three pulses, 1, 2, and 3 are detected at different times t. Two discriminators emit a counting signal if their set voltage-level is reached by a pulse. Pulse 2 triggers the Lower Level EL but not the Upper Level EU. Pulse 2 is thus counted into the spectral region denoted as P. The anti-coincidence counter prevents a pulse from being sorted into more than one region

A multichannel analyzer uses a fast ADC to record incoming pulses and stores information about pulses in one of two ways:[1]

Pulse-height analysis

In pulse-height analysis (PHA) mode, the pulses are counted based on their amplitude. The number of different amplitudes that are counted depends on the number of channels of the MCA, but is normally in the range of a few thousand. In this way a histogram of frequency against pulse amplitude (or "height") can be produced and either sent to a computer, shown on a screen or (in older models) directly printed. This mode can be used to analyze energy distribution of various nuclear processes, including nuclear decay:[2] this is the process used in alpha-, beta-, and gamma spectroscopy.

Multichannel scaling mode

In multichannel scaling (MCS) mode, the pulses are counted in a given time period, and in the channel the pulses are input as changes over time (rather than with amplitude as in PHA mode). The trigger for changing channel can be used for changing other parameters of an experiment, allowing an MCA to be used as an X–Y recorder. This mode can be used in conjunction with a Geiger counter to see a change in radioactivity over time.

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See also

References
  1. "THE MULTICHANNEL ANALYZER" (PDF). Western University. Retrieved 27 March 2016.
  2. "Gamma Spectroscopy with a Scintillation Detector and Multichannel Analyzer" (PDF). American University in Bulgaria. Retrieved 27 March 2016.


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