Keyword:SSFGEOMETRY
SSFGEOMETRY type length1 <length2>
This keyword introduces the use of the universal sigmoid curve model of self-shielding to account approximately for the reduction of the neutron flux by cross section resonances.
The first integer parameter type defines the type of target geometry and the following one or two real parameters specify the size of the target, in units of cm. Permitted values of type are 1-4, with interpretations as follows:
| type | Target shape | length1 | length2 |
|---|---|---|---|
| 1 | foil | thickness | (not used) |
| 2 | wire | radius | (not used) |
| 3 | sphere | radius | (not used) |
| 4 | cylinder | radius | height |
where foil targets are taken to be of infinite transverse extent and wires are taken to be infinitely long. The self-shielding factors are calculated using the resolved resonances of the nuclides specified with the SSFFUEL keyword, or indirectly using the SSFMASS keyword. In the latter case, the natural abundance data stored internally in FISPACT-II are used to calculate the numbers of atoms of the individual nuclides.
For foil (type = 1) or wire (type = 2) targets, the numbers of atoms specified are interpreted as being per unit area or length, respectively.
Note that SSFGEOMETRY and PROBTABLE must not both be used in a particular case.
An example of the use of this keyword is
Example usage:
< -- Control phase -- > ... GETXS 1 709 SSFMASS 0.000193 1 W 100.0 SSFGEOMETRY 1 0.01 FISPACT * Title of the simulation < -- Initial phase -- > ... < -- Inventory phase -- > ...
In this case pure tungsten is specified. A foil 0.1 mm thick containing 0.193 grams per square centimetre of tungsten with the five stable isotopes in their natural abundances is to be used in the self-shielding calculation.
The SSFGEOMETRY keyword in this section applies to the collapse calculation initiated by the FISPACT keyword. The keyword may also appear in the inventory calculation section in conjunction with further GETXS keywords.
