Energy Resolution An important aspect of a g -ray spectrometer is the ability to
discriminate between g-rays with slightly different energy. This
quality is characterized by the so-called energy resolution which is defined as the
width (FWHM) of the photopeak at a certain energy.
Besides by the g -ray energy,
the energy resolution is influenced by :
- The light output of the scintillator
,
- The size of the scintillator (light collection)
,
- Photomultiplier characteristics (quantum efficiency and photocathode homogeneity)
At low energies where photoelectron statistics dominate the energy resolution, the
energy resolution is roughly inverse proportional to the square root of the g-ray energy.
The energy resolution of a scintillation detector is
a true detector property, limited by the physical characteristics of the
scintillator and the PMT or other readout device.
A typical energy resolution for 662 keV g-rays absorbed in small NaI(Tl) detectors is 7.5 % FWHM. At low
energies, e.g. at 5.9 keV, a typical value is 45 % FWHM. At these low energies, surface
treatment of the scintillation crystal strongly influences the resolution. It may be clear
that especially at low energies, scintillation detectors are low resolution devices unlike
Si(Li) or HPGe detectors. |