Inspection of⁵⁶Feγ-Ray angular distributions as a function of incident neutron energy using optical model approaches

Abstract

Abstract. Neutron inelastic scattering cross sections measured directly through (n,n) or deduced from γ -ray production cross sections following inelastic neutron scattering (n,n γ ) are a focus of basic and applied research at the University of Kentucky Accelerator Laboratory (www.pa.uky.edu/accelerator). For nuclear data applications, angle-integrated cross sections are desired over a wide range of fast neutron energies. Several days of experimental beam time are required for a data set at each incident neutron energy, which limits the number of angular distributions that can be measured in a reasonable amount of time. Approximations can be employed to generate cross sections with a higher energy resolution, since at 125 o , the a 2 P 2 term of the Legendre expansion is identically zero and the a 4 P 4 is assumed to be very small. Provided this assumption is true, a single measurement at 125 o would produce the γ -ray production cross section. This project tests these assumptions and energy dependences using the codes CINDY/SCAT and TALYS/ECIS06/SCAT. It is found that care must be taken when interpreting γ -ray excitation functions as cross sections when the incident neutron energy is < 1000 keV above threshold or before the onset of feeding.

Templates of expected measurement uncertainties for (n, xn) cross sections

“…Sometimes the measurements are made at a single angle, 55 • or 125 • degrees, where the Legendre coefficient P 2 is identically zero, and one can easily deduce the angle-integrated cross sections if one assumes the a 4 and all higher coefficients are zero. Making this assumption could lead to 5-15% errors near the γ-ray threshold for E2 transitions [39]. (Typically less further above threshold.)…”

“…assumption is not valid near the level's threshold, and several additional angles are now generally measured to produce a reliable result [15,16,39]. Partial information on other reactions such as (n, 2n), (n, 3n), (n, p), etc., can be obtained with similar highresolution γ-ray measurements.…”