Gamma spectroscopy is a radiochemistry measurement method which determines the energy and count rate of gamma rays emitted by radioactive substances.

EO 2.8DESCRIBE the operation of a gamma spectrometer to include:

a.         Type of detector used

b.         Multichannel analyzer operation

Gamma spectroscopy is a radiochemistry measurement method that determines the energy and count rate of gamma rays emitted by radioactive substances. Gamma spectroscopy is an extremely important measurement. A detailed analysis of the gamma ray energy spectrum is used to determine the identity and quantity of gamma emitters present in a material.

The equipment used in gamma spectroscopy includes a detector, a pulse sorter (multichannel analyzer), and associated amplifiers and data readout devices. The detector is normally a sodium iodide (Nal) scintillation counter. Figure 27 shows a block diagram of a gamma spectrometer.

Figure 27 Gamma Spectrometer Block Diagram

The multichannel pulse height analyzer is a device that will separate pulses based on pulse height. Each energy range of pulse height is referred to as a channel. The pulse height is proportional to the energy lost by a gamma ray. Separation of the pulses, based on pulse height, shows the energy spectrum of the gamma rays that are emitted. Multichannel analyzers typically have 100 or 200 channels over an energy range of 0 to 2 MeV. The output is a plot of pulse height and gamma activity, as shown in Figure 28. By analyzing the spectrum of gamma rays emitted, the user can determine the elements which caused the gamma pulses.

Figure 28 Multichannel Analyzer Output

Summary

The operation of a gamma spectrometer is summarized below.

Gamma Spectrometer Summary

A gamma spectrometer uses a scintillation counter, normally Nal.

A multichannel analyzer separates the pulses based on pulse height.

Since each radioactive material emits gammas of certain energy levels, each pulse height corresponds to a different type of atom.

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