Difference between revisions of "X-ray absorption & fluorescence"
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The X-ray beam intensity (of wavelength = Lambda) at depth x into a material is calculated by Beer-Lambert law: | The X-ray beam intensity (of wavelength = Lambda) at depth x into a material is calculated by Beer-Lambert law: | ||
I(x) = Io e^(-x | I(x) = Io e^(-mu * x) | ||
The '''Absorption Length''' is then defined as the distance into a material where the incident x-ray beam intensity (Io) has decreased to 1 / ''e'', or about 63%. (alternatively called ''Attenuation Length''). | The '''Absorption Length''' is then defined as the distance into a material where the incident x-ray beam intensity (Io) has decreased to 1 / ''e'', or about 63%. (alternatively called ''Attenuation Length''). | ||
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This is a convenient value because: | This is a convenient value because: | ||
(1/e) = e^(-x | (1/e) = e^(-mu * x) | ||
ln(1/e) = ln(e ^-x | ln(1/e) = ln(e^(-mu * x)) | ||
1 = x | 1 = mu * x | ||
x = 1/ | x = 1/mu | ||
example | |||
dfdf | |||
== Software == | == Software == | ||
Revision as of 01:49, 29 August 2011
General Infomation
See the X-ray Absorption Information (11BM page) http://11bm.xor.aps.anl.gov/absorption.html
Web Links
WebAbsorb: web based calculator to compute X-ray absorption for powder XRD capillary samples (11BM page) http://11bm.xor.aps.anl.gov/absorb/absorb.php
MuCal: calculate X-ray absorption, fluorescence and more (by C. Segre @ IIT/ANL http://csrri.iit.edu/mucal.html
Absorption Length
The X-ray beam intensity (of wavelength = Lambda) at depth x into a material is calculated by Beer-Lambert law:
I(x) = Io e^(-mu * x)
The Absorption Length is then defined as the distance into a material where the incident x-ray beam intensity (Io) has decreased to 1 / e, or about 63%. (alternatively called Attenuation Length).
Recall that Euler's number e = 2.718.
This is a convenient value because:
(1/e) = e^(-mu * x) ln(1/e) = ln(e^(-mu * x)) 1 = mu * x x = 1/mu
example
dfdf
Software
pyFPRIME and ABSORB
https://subversion.xor.aps.anl.gov/trac/pyFprime/
These two python GUI programs are used for computing approximate x-ray scattering cross sections (f, f' and f") for individual elements using the Cromer & Liberman algorithm.
FPRIME computes and plots elemental scattering factors.
ABSORB computes scattering and absorption for a given composition and makes an attempt to estimate density as well. ABSORB can be also accessed as a web utility (see http://11bm.xor.aps.anl.gov/absorb/absorb.php).
