Gamma Ray spectrometer:

Since each gamma ray may deposit a different fraction of its energy, the output voltage, pulses will not have identical pulse height, though its distribution will be characteristic.  Hence a scintillation detector is used for recording gamma ray spectrum and also for the determination of γ -ray energy.  A scintillating gamma ray

spectrometer often woks in two modes: differential and integral. Differential mode works as the principle of pulse height analysis and is used for recording complete gamma ray spectrum. However, integral mode is used for estimating the overall activity of the sample and different energies or radionuclides cannot be discriminated.

A typical gamma Ray spectrometer

For an ideal detector, a gamma spectrum of a typical source such as 137Cs in Figure shows a photo peak and a Compton edge. It is observed that the photo peak is broad and this broadening is measured in terms of full width at half maximum (FWHM) divided by pulse height or peak position value where maximum occurs expressed in percentage.