Broadenable Reactions

As demonstrated on the preceeding pages, temperature dependence can be introduced by Doppler broadening smooth cross sections at low energies (less than about 16kT/A). In addition, cross sections with features that are sharp with respect to kT/A, such as resonances, will show temperature dependence. Therefore, the reactions that need to be Doppler broadened are normally elastic, fission, and capture. Sometimes (n,alpha) reactions are present at low energies also. Cross sections in the unresolved resonance range cannot be broadened (see UNRESR and PURR).

The maximum energy for broadening, thnmax is defaulted to either the first reaction threshold (typically MT=51, the first inelastic level), the start of the unresolved energy range, or 1 MeV, whichever is the smallest. BROADR selects the set of reactions to be broadened by looking for those that are present in this energy range, which is usually elastic, fission, and capture.

It is possible that these reactions will show no changes under Doppler broadening over much of this energy range. For example, resonances in light isotopes tend to be broad with respect to thermal energies. However, we usually just go ahead and run BROADR on everything.

If you want to use NJOY cross sections for supernova calculations, you may want to include more reactions, such as the first few inelastic levels. There is an option with thnmax negative that allows this.


23 January 2013 T-2 Nuclear Information Service