Project 14b: Linear Absorbtion Coefficient

for Quasicrystals in [1/cm]

Steffen Weber, July 1998 


see 14a: Crystals

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Quasicrystal are aperiodic structures, which do not have a defined unit cell in 3D-space. They have a higher-dimensional unit cell of volume V. depending on the structure model this unit cell is filled with occupation domains (atomic surfaces). The summation over their volumes gives Vi the internal space volume. We can then define a point density pd= Vi/V. Since this depends on the applied structure model it will be calculated in the corresponding refinement program. That value for the point density should be used here, in order to calculate the lin.absorbtion coefficient for quasicrystals.

I am still checking the results of this applet for quasicrystals


usage

  1. give the chemical formula in the format 1.Element [SPACE]nAtom [SPACE] 2.Element [SPACE] nAtom [SPACE]...
    the elements can be given in any format (eg: Na na NA for sodium)
    nAtom may be a non-integer value
    The given example is for Al70Mn17Pd13 The sum over nAtom has to be =100.
  2. give point density
  3. click execute

This applet calculates the linear absorbtion coefficient [1/cm] of quasicrystals for a given chemical formula and various X-ray wavelengths (Ag,Mo,Cu,Fe,Cr K-alpha).

Atomic mass attenuation coefficients are used here for the calculation.

The calculated linear absorbtion coefficients are then used to plot a graph, which shows how much an incident beam intensity would be attenuated by passing through a slab of the material (thickness range: 0.0-1.1 mm). You may drag the vertical marker line to facilitate the readout.

The legend lists the various linear absorbtion coefficients, the mass per formula and the calculated density [g/cm^3].

The data for the atomic mass attenuation coefficients are taken from the International Tables of Crystallography, Vol C, 1992 and are implemented in the code.

wavelengths for K-alpha in Angstrom:
Ag (0.5608), Mo (0.7107), Cu (1.5418), Fe (1.9373), Cr (2.2909)