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What
makes a good detector?
Fluorine
resolution FKα FWHM
The width of the peaks in a
spectrum will vary depending on the energy of the X-ray line. In Fig. 8 this
variation with energy has been calculated to show how the resolution should
change with X-ray energy for Si(Li) and HpGe detectors with different Mn
resolution specifications. The curves are calculated from the equation
FWHM2 = k . E + FWHMnoise2
where k is a constant for the
detector material, and E is the energy.
These curves demonstrate that as
the energy decreases, the resolution of the X-ray peaks improves. The
variation is also clearly different for Si(Li) and HpGe crystals. At low
energy the electronic noise contribution (FWHMnoise) has a
greater effect on resolution (Fig. 9). Mn FWHM is a very insensitive measure
to characterize the noise of a detector and predict the resolution at low
energy. Therefore to characterize the resolution of a detector at low
energy, the resolution is also quoted for another line, typically fluorine
Kα.
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