CHROMIUM AND INELASTIC SCATTERING "DISCREPANCIES"

D. LARSON, ORNL

As far as we know, there are no "integral measurements" to check the quality of inelastic scattering data for nickel and . (For j~in, such integral data exist in terms of spheres). Stainless steel integral data are dominated by effects of iron, so are not very useful for the purpose at hand. The Livermore 14 MeV pulsed sphere measurements are sensitive to the energy and angular distributions of both discrete and continuum inelastic . scattering, so would be ideal tests if the data existed. In lieu of integral information, the problem must be addressed by looking at the quality of available differential data. With most evaluated libraries going to isotopic evaluations, the importance of isotopic differential data has increased. For 58Ni, data is available mainly for energies below 5 MeV, with a few data sets recently available (TUNL) from 8-17 MeV. The situation for 60Ni is similar. Guidance for the total inelastic scattering cross section is available from gamma-ray production measurements to 40 MeV (ORNL). For both of these , discrepancies larger than the uncertainties often exist among the various measurements. For the minor isotopes (61,62,64Ni) differential inelastic scattering data is generally sparse. Differential data for inelastic scattering from the natural materials is more plentiful, but also suffers from disagreements larger than the quoted uncertainties. There are several emission cross section measurements for natural Ni, but all are at an incident energy of 14 MeV. Some data sets provide detailed angular distributions for each outgoing energy spectra. For 52Cr, the two lowest lying levels have data to 8 MeV, but data for higher lying levels generally only goes to about 4 MeV. There is one measurement at 14 MeV for the two low lying levels. The total inelastic scattering cross section is available to 40 MeV, as for 58,60Ni. Data for the other isotopes (50,53,54Cr) is available only up to about 4 MeV. As for natural Ni, cross section data is available only at 14 MeV. Comparison of the various inelastic scattering data sets for chromium isotopes shows that they often disagree by more than their quoted uncertainties. For the region from 8-14 MeV, important to fusion energy technologies, the data base for the isotopes of nickel and chromium is inadequate. More differential data (including neutron emission data) is needed in this region to improve the evaluations and reduce the uncertainties for these materials. For fast reactor studies, high resolution inelastic scattering data in the resonance region (and just above, as exists for iron) would remove the unphysical, smooth cross sections.

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