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USESPALLATION cutoff-energy nnuc
nuc(i), i=1,nnuc

This keyword, added in version 4.0, merges data from the cross-section library on stream xs_endf with the spallation cross-section data on stream sp_endf. The merged cross-section data files are stored in the directory mapped to stream xs_extra.

The cutoff-energy is given in MeV and specifies the energy at which the use of xs_endf is switched to sp_endf. The nnuc value specifies the number of isotopes that are to be spliced. If 0 is set for nnuc, the keyword causes all isotopes to be spliced for which there is both a file in xs_endf and sp_endf. Following these options, the user must specify the nnuc number of isotopes.

An example of the use of this keyword is:

GETXS 1 162

In this case the set of stable lead isotopes are spliced for proton-induced reactions. Note that the HEIR library, released with FISPACT-II version 4.0 and above, provides proton-induced reaction data for 2095 isotopes, typically with over 1000 residual products per file. This can introduce several million entries to the rate equation matrix, requiring significantly more computer resources. An example calculation is provided in the getting started examples.

The library merging only needs to be done once for a given cutoff energy. Subsequent collapse runs may be performed using the USEXSEXTRA keyword. NOTE that the library files from previous runs will be used if they remain in the xs_extra directory. It is recommended that the contents of the xs_extra directory be removed before subsequent runs using the USESPALLATION are performed.