Neutron capture in 238U

Abstract The γ-ray spectrum following slow neutron capture in 238 U has been measured as a function of incident neutron energy at the Brookhaven HFBR fast neutron chopper. The decay scheme proposed by previous (d, p) and high resolution thermal (n, γ) measurements has been substantially verified. Partial radiation widths for s-wave resonances up to 117 eV have been deduced. By using a simple multi-level analysis, the spectra between resonances from 21 eV down to thermal have been fitted. The behavior of the strong transitions to low-lying l = 1 states is explained using a direct capture model, while the transitions to low-lying collective states can be explained by level-level interference. The distribution of El transition strengths is not consistent with a χ 2 distribution of one degree of freedom.