Model predictions of the fission-product yields for 238 U Part IV: Selected case studies

The results of model calculations on nuclide yields produced in se- lected scenarios using reactions with 238 U nuclei are presented. The calculation combines the modelling of the initial reaction mechanism, the deexcitation proc- ess including the fission competition with the prediction of the nuclide production in the fission of excited 238 U and all daughter nuclei produced in the evaporation cascade. The calculations are relevant for the design of future secondary-beam fa- cilities. The present work is the forth of a series of reports on predicted fission-product yields for 238 U. In the first part, we describe the details of the semi-empirical fission code PROFI used for the calculations. The model is a more advanced version of the statistical saddle-scission model described in ref. (1). In the second part, we present the predictions for the nuclide pro- duction by first-chance fission of 238 U at different excitation energies. In the third part, we calculate the complete nuclide production obtained from fission, when 238 U is excited to dif- ferent excitation energies. This calculation includes multi-chance fission. The forth part pres- ents predictions on nuclide production by fission reactions, using 238 U as a target or projectile nucleus, under a few selected experimental conditions. In these cases, many fissioning nuclei in a large excitation-energy range may contribute to the fission yields. Finally, in the fifth part we compare the model predictions with available data. The nucleus 238 U is of prime importance for technical applications due to its high abun- dance. Further, it is the most neutron-rich fissile nucleus found in nature and, therefore, it seems to be well suited for the production of neutron-rich nuclides by fission in secondary- beam facilities. The calculations have been performed using the dedicated nuclear-reaction code ABRA which describes electromagnetic excitations (see (2)) and high-energy nuclear collisions (see (3)). The deexcitation process is calculated with the evaporation code ABLA (4). The formu- lation of the level densities including collective excitations is documented in (5). Dissipative effects in the fission process are included as described in Refs. (6,7). The nuclide production in fission is calculated with the PROFI code (1). Interactions of electrons and gamma rays with matter have been evaluated with the GEANT code. The figures give an overview on calculated nuclide production in fission in some selected reactions with 238 U nuclei. The results are shown on the chart of the nuclides, as mass and nuclear-charge distributions and as isotopic distributions. Even-odd fluctuations in the iso- topic cross sections are not realistic. They originate from a slightly inconsistent treatment of pairing effects in binding energies and level densities.