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GETXS libxs <ebins>

This keyword has two integer parameters. If the first parameter libxs is set to 0, then the second parameter should be omitted, and cross section data are read from the existing collapsed library (collapx file) specified in the files file. If libxs is 1, then the second parameter ebins gives the number of energy bins to be used in collapsing the cross section data from the ENDF library files and fluxes or arb_flux files specified in the files file. If libxs is -1, then the ENDF data are read from the compressed binary version of the ENDF data stored in the file specified by xs_endfb in the files file. Note that the value libxs = -1 is not valid for legacy EAF libraries. For information on the preparation of the compressed binary ENDF data files see this page.

The GETXS keyword may also be used in the initial conditions and inventory calculation phases to modify the cross sections, for example to handle time-dependent projectile spectra and temperature changes in cross-sections.

The number of energy groups ebins must be consistent with the number of groups in the supplied library file. The permitted numbers of groups for cross-section data are, for the most recent public distribution, the CCFE-709 for neutrons and CCFE-162 for charged particles. Legacy EAF libraries and their various group structures may also be used.

Example usage, where the cross sections are re-collapsed every 20 days during some irradiation simulation:

< -- Control phase -- >
 GETXS 1 709
 * Title of the simulation
 < -- Initial phase -- > 
 < -- Inventory phase -- > 
 GETXS 1 709
 GETXS 1 709
 GETXS 1 709

If ebins equals 1, then the user can specify an arbitrary energy bin structure via the enbins input file. This file should give a description of the energy bin structure, followed by the number of groups (i.e. the actual ebins to be used), and then a list of comma-separated ebins+1 energy boundaries in decreasing eV order. An example of such a file for the 175-group "Vitamin-J" structure is:

 1.96403E7, 1.73325E7, 1.69046E7, 1.64872E7, 
 1.56831E7, 1.49182E7, 1.45499E7, 1.41907E7, 1.38403E7, 1.34986E7, 1.28403E7, 1.25232E7, 1.22140E7, 1.16183E7, 
 1.10517E7, 1.05127E7, 1.00000E7, 9.51229E6, 9.04837E6, 8.60708E6, 8.18731E6, 7.78801E6, 7.40818E6, 7.04688E6, 
 6.70320E6, 6.59241E6, 6.37628E6, 6.06531E6, 5.76950E6, 5.48812E6, 5.22046E6, 4.96585E6, 4.72367E6, 4.49329E6, 
 4.06570E6, 3.67879E6, 3.32871E6, 3.16637E6, 3.01194E6, 2.86505E6, 2.72532E6, 2.59240E6, 2.46597E6, 2.38513E6, 
 2.36533E6, 2.34570E6, 2.30693E6, 2.23130E6, 2.12248E6, 2.01897E6, 1.92050E6, 1.82684E6, 1.73774E6, 1.65299E6, 
 1.57237E6, 1.49569E6, 1.42274E6, 1.35335E6, 1.28735E6, 1.22456E6, 1.16484E6, 1.10803E6, 1.00259E6, 9.61672E5, 
 9.07180E5, 8.62936E5, 8.20850E5, 7.80817E5, 7.42736E5, 7.06512E5, 6.72055E5, 6.39279E5, 6.08101E5, 5.78443E5, 
 5.50232E5, 5.23397E5, 4.97871E5, 4.50492E5, 4.07622E5, 3.87742E5, 3.68832E5, 3.33733E5, 3.01974E5, 2.98491E5, 
 2.97211E5, 2.94518E5, 2.87246E5, 2.73237E5, 2.47235E5, 2.35177E5, 2.23708E5, 2.12797E5, 2.02419E5, 1.92547E5, 
 1.83156E5, 1.74224E5, 1.65727E5, 1.57644E5, 1.49956E5, 1.42642E5, 1.35686E5, 1.29068E5, 1.22773E5, 1.16786E5, 
 1.11090E5, 9.80365E4, 8.65170E4, 8.25034E4, 7.94987E4, 7.20245E4, 6.73795E4, 5.65622E4, 5.24752E4, 4.63092E4, 
 4.08677E4, 3.43067E4, 3.18278E4, 2.85011E4, 2.70001E4, 2.60584E4, 2.47875E4, 2.41755E4, 2.35786E4, 2.18749E4, 
 1.93045E4, 1.50344E4, 1.17088E4, 1.05946E4, 9.11882E3, 7.10174E3, 5.53084E3, 4.30742E3, 3.70744E3, 3.35463E3, 
 3.03539E3, 2.74654E3, 2.61259E3, 2.48517E3, 2.24867E3, 2.03468E3, 1.58461E3, 1.23410E3, 9.61117E2, 7.48518E2, 
 5.82947E2, 4.53999E2, 3.53575E2, 2.75364E2, 2.14454E2, 1.67017E2, 1.30073E2, 1.01301E2, 7.88932E1, 6.14421E1, 
 4.78512E1, 3.72665E1, 2.90232E1, 2.26033E1, 1.76035E1, 1.37096E1, 1.06770E1, 8.31529  , 6.47595  , 5.04348  , 
 3.92786  , 3.05902  , 2.38237  , 1.85539  , 1.44498  , 1.12535  ,8.76425E-1,6.82560E-1,5.31579E-1,4.13994E-1, 
 1.00001E-1, 1.0E-5 

Files for this and other standard energy bin structures can be downloaded below.

Media:Ebins 66.txt Media:Ebins 69.txt Media:Ebins 100.txt Media:Ebins 162.txt
Media:Ebins 172.txt Media:Ebins 175.txt Media:Ebins 211.txt Media:Ebins 315.txt
Media:Ebins 351.txt Media:Ebins 586.txt Media:Ebins 616.txt Media:Ebins 709.txt
Media:Ebins 1102.txt

Note that the user is responsible for linking to (and if necessary creating) nuclear data files in the specified group format.

Warning: For advanced users only. The standard solution to the common problem of having a flux spectrum in a non-standard energy group structure is to apply the GRPCONVERT keyword and convert the flux spectrum into one of the standard group formats (above).