Fission Fragment Yield, Cross Section and Prompt Neutron and Gamma Emission Data from Actinide Isotopes

摘要

Recent experimental investigations on major and minor actinides at the JRC-IRMM are presented. Fission-fragment distributions of isotopes with vibrational resonances in the sub-threshold fission cross section, i. e. ~(234,238)U, have been measured. For ~(234)U, the impact of an increased neutron multiplicity for the heavy fragments with higher incident neutron energies has been studied as observed in experiment and also recently theoretically predicted. The impact is found to be noticeable on post-neutron mass yields, which are the relevant quantities for a-priori waste assessments. The fission cross sections for ~(240,242)Pu threshold and in the plateau region are being investigated within the ANDES project. The results show some discrepancies to the ENDF/B-Ⅶ.1 evaluation mainly for ~(242)Pu around 1 MeV, where the evaluation exhibits a resonance-like structure not observed so clearly in the present work. The requested target accuracy in design studies of innovative reactor concepts like Gen-Ⅳ is in the range of a few percent. In order to be able to respond to requests for measurements of prompt neutron and γ-ray emission in fission JRC-IRMM has also invested in setting up a neutron and γ-ray detector array. The neutron array is called SCINTIA and has so far been tested with ~(252)Cf(SF). For γ-ray multiplicity and spectrum measurements of ~(252)Cf(SF) and ~(235)U(n_(th), f) lanthanum- and cerium-halide detectors were successfully used.