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# Elastic Scattering Data

• First describe needed data ...
• Given differential cross section ,
, define total cross section:

• And diffusion cross section:

• Using semi-classical calculations for
(cf. Schultz), is finite.
• Still expect many small angle scatterings.
• Devise procedure to ensure efficiency.
• Note: even more efficient procedures
are being considered.

• First, write

• , ,
• N chosen large enough to satisfy accuracy.
• Must minimize error in
accurate momentum transfer.
• Integrate directly,
• Equate with corresponding approx. form,
• and C(Er).
• Then, know RHS of

• Divide -space into K equal probability bins:

• Find the , such that

• To sample , interpolate a uniform
random number into these bins.

• Essential data required for elastic scattering are:
1. ,
2. ,
3. I(1,0)(Ti,E0) used to find and

4. I(1,1)(Ti,E0) (ditto),
5. I(1,2)(Ti,E0) (ditto),
6. C(Er), for k=1,n.
• I(l,n) are integrations over Maxwellian
ion distribution (Reiter 1993):

• where and .

• Storage and implementation
• Same format as for all other reactions
(netCDF files),
• Note self-describing aspects
1. Name of reaction,
2. Number of dependent variables,
3. Organization of data for each dep. var.
(``table'' or ``fit''),
4. Rank of each dep. var. (number
of independent variables),
5. Character name for each dependent
and independent variable,
6. Number of values of each
independent variable (for tabular data),
7. Data tables
• Separate multidimensional array
for each dep. var. (see below, however).

• At run time, read in reaction data files
needed (and only those),
• All and data stored in one large array,
• For computing 's,
• And selecting collision partners
(heavy particle reactions),
• See flowchart.
• Stored as 1-D;
• Multi-dimensionality through explicit macros.
• Other data lumped into ``misc. data'' array,
• Used to ``process'' a given collision,
• Types of data required vary with process,
• And even with model for a given process.
• retain dep. var. labels from input file.
• For each variation is a subroutine
which knows how to use those data,
• Ideally, would be encoded alongside data in file (a ``method'' for that ``class'').
• Indexing into arrays is by ``problem
reaction number'' and dep. var. number.

Next: Surface Physics Data Up: Atomic and Surface Physics Data in DEGAS 2 Previous: Introduction

Daren Stotler
Fri Mar 29 15:28:56 EST 1996