Fast-neutron inelastic scattering cross sections for the principal even-even actinide nuclei. III.240,242,244Pu(n,n')

Abstract

For pt.II see ibid., vol.12, p.443, 1986. The review of fast-neutron inelastic scattering data for the principal even-even actinide nuclei, as undertaken previously for 232Th(n,n') and 238U(n,n') level excitation functions and angular distributions, is here continued for 240,242,244Pu(n,n') from threshold to 2.5 or 3.5 MeV. Differential and total (angle-integrated) cross sections have been calculated on the basis of proposed collective-band level schemes in the 'standard' (CN+DI) formalism and in the statistical S-matrix formalism of Hofmann, Richert, Tepel and Weidenmuller (the HRTW approach). For consistency throughout, the optical potential and deformation parameters have followed the Bruyeres prescription, except that for 244Pu Nilsson harmonic-oscillator deformation parameters were chosen. Corrections were applied to the compound-nucleus (CN) cross sections to take account of Moldauer level-width fluctuations, extra n'-channel and radiative-capture competition; for 240,242Pu+n, fission competition was also taken into account and for 242,244Pu+n, provision for continuum competition was also made. So far as possible, theoretical data were compared with (the sparse and somewhat unreliable) experimental results and with the ENDF/B-V evaluation: for 240Pu(n,n') the only available measured data were level excitation functions to En=1.5 MeV for the 2+, 4+ and 6+ states in the ground-state rotational band and for grouped 'composite' vibrational levels; for 242Pu(n,n') the experimental excitation function and angular distribution data extended to En=3.4 MeV for the 2+ and 4+ rotational states; no data existed for 244Pu(n,n'). The body of calculated cross-section data thus serves as a comprehensive database for the primary rotational and vibrational states in the three principal even-mass fertile Pu isotopes, wherein the HRTW angle-integrated values demonstrate the viability of this as yet underexploited method.