Evaluation of neutron nuclear data of praseodymium-141 and -143

Abstract

For the next version of JENDL general purpose file, neutron nuclear data on 141,143 Pr are evaluated considering cross sections and spectra provided from experiments in the fast neutron energy region up to 20 MeV. Total and elastic cross sections are derived from optical model. Pre-equilibrium and direct-reaction processes are taken into account in addition to the compound process. The statistical model is applied to calculate the cross sections above the resolved resonance region. For unstable 143 Pr nuclide having less experimental data, we use the same parameters as 141 Pr for mass-dependent and -independent terms in the optical potential. The resolved resonance parameter remains unchanged from JENDL-4.0. The present evaluations give consistent results with experimental data, reflecting newly measured one. The evaluated data are compiled in ENDF-6 format for the next version of JENDL.Keywords: evaluation; neutron nuclear data; cross section; spectrum; fission product; praseodymium-141; praseodymium-143 IntroductionThe fourth version of the Japanese Evaluated Nuclear Data Library (JENDL-4.0 [1]) was released in May 2010. In the library, 215 nuclides are regarded as fission products in the region from Z = 30 to 68. The resolved and unresolved resonance parameters for all of those nuclides were examined by reviewing experimental data; however, the fast neutron region above the resolved resonances was re-evaluated only for 174 nuclides. The remaining 41 nuclides, which were not examined for the release of JENDL-4.0, need to be re-evaluated for the next version of JENDL general purpose file.Praseodymium-141 and -143, which are the target isotopes of the present work, are included in the remaining 41 nuclides. As mentioned, the resolved resonance parameters were re-examined in JENDL-4.0; however, cross sections in the fast neutron region were not revised. The last update was performed in JENDL-3.2 released at 1994, and the calculation was performed by the statistical-model code CASTHY [2] with the competing reaction using PEGASUS [3]. Several experimental data measured after the release of JENDL-3.2, which show a different value from old one referred by JENDL-4.0 (i.e., −3.2), also inclines us re-evaluation. The purpose of this study is to improve the nuclear data in the fast neutron