Internal Multilayer Collimators
Resolution as a Function of Energy
Figure 1. X-ray fluorescence (XRF) of multi-element sample from109Cd.
Figure 2. Low (Z) element x-ray fluorescence (XRF) with 6 mm2/500 µm detector.
Figure 3. 241Am Spectrum.
The 6mm2/13mm2/25mm2 X 500 µm detectors exhibit "edge effects" due to partial charge collection at the edge of the detector which produce a secondary peak.
Figure 4. This plot shows a comparison between a collimated detector and a detector without a collimator.
Although a small effect, approximately 1% of the counts of the 5.9 keV peak, an internal multi-layer (see below) collimator is used on all 6mm2/13mm2/25mm2 X 500 µm detectors in order to remove the secondary peak.
A multilayer collimator is made by progressively using lower Z materials. Each layer acts as an absorber to the fluorescence peaks of the previous layer. The final layer will be of the lowest Z material whose fluorescence peaks are of low enough energy to be outside the anticipated X-ray detection range.
Amptek has developed a state-of-the-art internal MultiLayer Collimator (ML). The base metal is 100 µm of tungsten (W), the first layer is 35 µm of chromium (Cr), the second layer is 15 µm of titanium (Ti), and the last layer is 75 µm of aluminum (Al).
Figure 10. Resolution as a function of energy for various detector resolutions. For example, a detector with an 55Fe resolution of 145 eV FWHM will follow the red curve.
Example: Find the 55Fe row in the above table and locate the resolution of the detector (bold). The column with that resolution lists the resolutions of that detector for these comon energies.
Amptek X-Ray Chart (K and L emission lines)
Revised September 7, 2011