How does time resolution change with energy of gamma rays?
Answers
(energy) resolution and detection efficiency of a detector (either NaI or HPGe) are not the same thing.
The energy resolution (Re) of a detector measures its ability to distinguish gamma-rays with close energies. The better the energy resolution, the better it can separate two adjacent energy peaks, which allows identifying different decays or radionuclides in the spectrum. Re is obtained from the peak full width at half of the maximum height (FWHM) using the following equation: Re = FWHM / E (%), where E is the related energy of the peak. Re is better (i.e., its % value is lower) for higher energies.
The detection efficiency measures the ability of the detector to convert gamma-rays into useful signals and is simply given by the ratio of detected events per emitted gamma-rays. It depends mainly on the thickness (x) of the detector material, according to the formula: Det. eff. = 1 - e^(u.x) , where u is the linear attenuation coefficient of the material, at a given energy. For the same x, the efficiency decreases for increasing energies.