Measurements of the differential cross sections for elastic and inelastic scattering of 14 MeV neutrons in natural chromium, iron, and nickel.

Abstract

The time-of-flight technique was used with the 'ring' scattering geometry in a laboratory with low neutron scattering background to measure the angular distributions of the cross sections for elastic and inelastic scattering of 14 MeV neutrons in natural chromium, iron, and nickel. Specifically for inelastic scattering included were: the 1.43 MeV and 4.56 MeV levels of $\sp{52}$Cr, the 0.85 MeV level, and (2.94-3.12) MeV and (4.46-4.51) MeV level groups of $\sp{56}$Fe, the 1.33 MeV level of $\sp{60}$Ni combined with the 1.45 MeV level of $\sp{58}$Ni, and the 4.48 MeV level of $\sp{58}$Ni. Pulses of neutrons with time width of 1.2-1.6 ns were produced via the $\rm\sp3H(d,n)\sp4He$ reaction in a 150 keV Cockcroft-Walton linear accelerator. The energy of the incident neutrons was between 14.75 MeV (at 16$\sp0)$ and 13.55 MeV (at 150$\sp0).$ High purity scattering ring samples were used. The scattering angles ranged from ${\sim}16\sp0$ to ${\sim}150\sp0$ with a typical step of ${\sim}10\sp0.$ Ring samples with high purity were used. The primary neutron detector was a heavily shielded 20 cm x 8.2 cm cylindrical NE-213 liquid organic scintillator. The neutron detection efficiency was calculated with the Monte Carlo method and was also measured with a $\sp{252}$Cf source. The data were corrected for background, multiple scattering, air scattering, etc. The overall uncertainty for the elastic scattering cross section was in the range of 7-8% for all three materials. The uncertainties for the inelastic scattering cross sections were estimated to be between 8 and 24%. The measured angular distributions were compared with the evaluations in the ENDF/B-VI, JENDL-3, CENDL-2, BROND-2, and JEF-2 nuclear data libraries. For elastic scattering, there are no significant discrepancies in general, neither among the evaluations nor between the present data and the evaluations. For the inelastic scattering there are significant discrepancies both in shape and magnitude among the evaluations (when available) as well as between the present data and the evaluations. These data provide a valuable contribution to the scarce inelastic scattering data available in the literature. With an uncertainty of less than 10%, the elastic scattering data also provide a valuable supplement to the currently available data.