Estimating fission fragmentangular momentum using TALYS

Sammanfattning: The Division of Applied nuclear physics at Uppsala university, isregularly performing high-precision measurements on isomeric fissionyield ratios (IYR). Its aim is to explore the physics behind nuclearfission, in particular how angular momentum is generated. Thedepartment has developed a method to obtain the root mean square(rms) values of the primary fission fragment angular momentumdistribution (Jrms). However, several assumptions are made in themodel; thus this project aims to assess the sensitivity of the modelparameters. In particular, the focus is on assessing the mean andwidth of the excitation energy distribution, as well as thecorrelation between the excitation energy and the angular momentum.The task is to implement a method that builds upon the previousmodel. The method that was implemented is based on random sampling,which randomises values of the parameters in a specific rangedepending on the type of distribution.Three types of distributions (Normal, Rayleigh and Poisson) of theexcitation energy were tested, and it seemed to have little effecton the system. The fact that the distributions are symmetric orantisymmetric seemed to have negligible impact.The nucleus that was studied was 134I after the fission process withparent nucleus 235U in the thermal energy range. The IYR was plottedagainst four parameters: Jrms, a proportionality constant (A)between the energy and angular momentum, the intrinsic energy (Eint)and the spread of the energy (E).Their mean values and spread wasacquired from a fission simulations software called GEF. Using theseas inputs to another software TALYS, one can acquire the isomericyield ratios (IYR) for the nucleus with different neutron channels.Jrms has the most impact, and had a clear interval which gave a IYRvalue close to experiments. The three other parameters showed noclear correlation which results in the conclusion: the IYR says verylittle about the fragments excitation energy but quite a lot aboutits angular momentum in the case of 134I with the assumptions made.