Multichannel analyzer

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A graph of number of counts against channel number
The output of an MCA used in PHA mode to analyze Cs-137

A multichannel analyzer (MCA) is a laboratory instrument used to analyze an input signal that primarily consists of pulses.[1] MCAs are used extensively in digitising various laboratory experiments, especially those related to nuclear physics,[2] including gamma spectroscopy. MCAs are typically interfaced with via USB or Ethernet, but can also use PCI or RS232.


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

Pulse-height analysis[edit]

In pulse-height analysis (PHA) mode, the pulses are counted based on 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.[3] 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[4] or (in older models) directly printed. This mode can be used to analyze the energy distribution of various nuclear processes, including nuclear decay:[5] this is the process used in gamma spectroscopy.

Multichannel scaler[edit]

In multichannel scaler (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.

See also[edit]


  1. ^ a b "THE MULTICHANNEL ANALYZER" (PDF). Western University. Retrieved 27 March 2016.
  2. ^ "Multichannel Analyzers". Retrieved 27 March 2016.
  3. ^ "Multichannel Analyzers". Archived from the original on 13 March 2016. Retrieved 27 March 2016.
  4. ^ "MCA with screen" (PDF). Retrieved 27 March 2016.
  5. ^ "Gamma Spectroscopy with a Scintillation Detector and Multichannel Analyzer" (PDF). American University in Bulgaria. Retrieved 27 March 2016.