Abstract
The issue of detecting the XAFS signal from dilute samples is discussed in detail with the aim of making best use of high flux beamlines that provide up to 10(13) photons s(-1). Various detection methods are compared, including filters with slits, solid state detectors, crystal analyzers and combinations of these. These comparisons rely on simulations that use experimentally determined parameters. It is found that inelastic scattering places a fundamental limit on detection, and that it is important to take proper account of the polarization dependence of the signals. The combination of a filter-slit system with a solid state detector is a promising approach. With an optimized system good performance can be obtained even if the total count rate is limited to 10(7) Hz. Detection schemes with better energy resolution can help at the largest dilutions if their collection efficiency and count rate limits can be improved.
Highlights
One of the big advantages of the X-ray absorption fine structure (XAFS) method is the ability to obtain detailed chemical and structural information about very dilute components of a sample
While the emphasis is on XAFS applications that typically require good signal to noise, many of the same considerations apply to other applications of X-ray fluorescence such as X-ray fluorescence microprobes for imaging
In this case it is clear that a high-count-rate solid state detector is the best choice
Summary
One of the big advantages of the X-ray absorption fine structure (XAFS) method is the ability to obtain detailed chemical and structural information about very dilute components of a sample. Typically Si or Ge, have energy resolution good enough to separate the fluorescence from most of the background Their main limitation is a maximum counting rate of about 105–106. Non-focusing arrangements are much better at collecting large solid angles, but because large area detectors are needed they can allow more background to leak through In this paper, both experiment and analysis is used to compare the various detector methods, with the aim of guiding future development to take best advantage of high flux beams. Both experiment and analysis is used to compare the various detector methods, with the aim of guiding future development to take best advantage of high flux beams It starts with a consideration of the signals available and ultimate performance possible with an ‘ideal’ detector
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