X-ray absorption & fluorescence

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

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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).