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A multichannel analyzer (MCA) is a piece of laboratory instrument used to analyze an input signal that primarily consists of pulses. They are used extensively in digitalising various laboratory experiments, especially those related to nuclear physics, including gamma spectroscopy. MCAs are typically interfaced with via USB or Ethernet, but can also use PCI or RS232.
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Operation
A multichannel analyzer uses a fast ADC to record incoming pulses and stores pulse information in one of two ways:
Pulse-height analysis
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. 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 the energy distribution of various nuclear processes, including nuclear decay: this is the process used in gamma spectroscopy.
Multichannel scaler
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.