<* $Id: xnd_rdif.html,v 1.1.1.1 2000/00/13 11:10:00 berar Exp $ *> XND diffusion file and formats.

XND diffusion file and formats.


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the default file: xnd_dif.d

In order to avoid a retyping of diffusion tables in the xnd input file, some tableshave been stored in the xnd_dif.d file which is by default located in the same directory than the xnd program.

When a diffusion factor is needed, the program first scans its internal table read in the input file then tries to find a matching entry in the xnd_dif.d file. This file contains entry for neutrons and x-ray but the anomalous scattering factor are not stored inside .Values in the file comes from the ITC( vol IV. p xx for neutron and p99-100 for analytical x-ray)

The different entries in the file are recognised by the name used in the variable DifName. For each diffusion name given in the atomic description of the phase, the program look for an entry which depend of the experiment.

DifNameFe57FeFe2+57Fe2+
neutrons0Fe57Fe0Fe57Fe
x-rayFeFeFe2+Fe2+

Neutron entry

They always begin with a digit as the neutron entries allow to distinguish various isotops. The natural or mean isotop has is referred as 0. The program uses the values of the diffusion length.

1 value
DifNameDifCoef
0Al0.365

X-ray scattering: analytical expression

These entries always begin with a letter to be distinguished from neutron entries. Values in the table comes from the ITC( vol IV. p99-100)

9 values
DifNameDifCoef[0]DifCoef[1]DifCoef[2]DifCoef[3]DifCoef[4] ...
CE 21.1671 2.81219 19.7695 0.226836 11.8513 ...

X-ray scattering: interpolation

These entries always begin with '*' to be recognized, this character is not stored in the internal table where *fe becomes Fe.

N values taken at
DifNameNds ds=0 s=ds s=2*ds s=3*ds ...
DifCoef[0]DifCoef[1]DifCoef[2]DifCoef[3]DifCoef[4] ....

Neutron magnetic entry

These entries always begin with '-' or '_' to be recognized, this character is not stored in the internal table where -fe becomes Fe.

Analytical expression

These entries always begin with '-'. Values for Jo can be read according the expansion Aexp(-as2)+...+D according to the ITC(vol C, p391-393)

7 values
DifNameDifCoef[0]DifCoef[1]DifCoef[2]DifCoef[3]DifCoef[4] ...
-FE3+ 0.397213.2440.62954.903-0.0314 ...

Interpolation

These entries always begin with '_'.

N values taken at
DifNameNds ds=0 s=ds s=2*ds s=3*ds ...
DifCoef[0]DifCoef[1]DifCoef[2]DifCoef[3]DifCoef[4] ....

Examples

The following lines are valid entries taken out of the xnd_dif.d file.
 0AL   0.345
 0AG   0.61

 CE    21.1671 2.81219 19.7695 0.226836 11.8513 17.6083 3.33049 127.113 1.86264
 CE4+  20.3235 2.65941 19.8186 0.218850 12.1233 15.7992 0.144583 62.2355 1.59180

Other cases

Specific description have been reserved for some other cases which are not yet implemented. They use the interpolation format but the DifName does not begin with a '*', but with another special character depending on the matter. '&' deals with compton scattering, $ for incoherent neutron scattering ...
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JFB June 21th, 1996