Analysis of Scintillation Detector Energy Spectra

Nal(Tl) scintillators are seldom used as gamma-ray spectrometers because their 

If a Nal(Tl) scintillator is used to detect a photon spectrum consisting of many gamma energies, the measured spectrum will be the summation of spectra 

Response functions of Nal(Tl) detectors, obtained by Heath et al., are shown in Fig. 12.17. These authors measured the response for several gamma energies and then used an interpolation scheme to derive the three dimensional plot of Fig. 12.17. A modified Gaussian of the form 

The energy resolution of Nal(Tl) detectors is quoted in terms of the percent resolution for the 0.662-MeV gamma of Cs. Using the best electronics available, this resolution is about 7 percent and the FWHM is about 46 keV. As mentioned in Chap. 9, the FWHM is roughly proportional to the square root of the energy. For this reason, the resolution in percent deteriorates as the energy decreases. For 10-keV X-rays, the best resolution achieved is about 40 percent, which makes the FWHM about 4 keV. 

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