Speaker
Description
The R-matrix method of Lane and Thomas is the standard procedure for modelling resonances at low energies, to determine widths and angular distributions needed for nuclear evaluations. Many different codes have been written, all with different input and output file formats. To ensure that results can be replicated, I have written a python code FERDINAND using FUDGE to read & write ENDF, GNDS standard formats, read AMUR, AZURE, EDA, FRESCO and RAC formats, and write AZURE, EDA, FRESCO, HYRMA and latex formats.
Because of the increasing need for gamma production information, R-matrix codes are being extended to include primary and secondary gammas and predict the angular distributions for both of kinds. More excited states of residual nuclei need to be included in the fits, since these give directly many of the secondary gamma decays. These place computational demands on the codes, and using Google’s Tensorflow framework enables the development of GPU codes such as LLNL’s RFLOW for fitting.
There is also a need to go higher-energy states in the compound nucleus. This will require theory developments to ensure smooth transitions from unresolved and/or overlapping resonances in an R-matrix code to Hauser-Feshbach predictions that are based on transmission coefficients derived from optical potentials. A good connection between these two methods should be possible because the Hauser-Feshbach method may be derived as an approximation to R-matrix resonance descriptions.
Reactions of n+14N and other reactions producing 15N* have been evaluated as part of the INDEN project. The thresholds for n+14N, p+14C and +11B are close to each other, and so all three channels must be fitted simultaneously. ENDF has a 1992 evaluation with these three channels up to 2 MeV, and Notre Dame has recently re-evaluated them up to higher energies. Here I report on assessments that include the higher excited states of 14N and 11B that are responsible for high-energy gamma production.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.