Cross section andγ-ray spectra forU238(n,γ) measured with the DANCE detector array at the Los Alamos Neutron Science Center

Abstract

Background: Accurate knowledge of the $^{238}\mathrm{U}$($n$,$\ensuremath{\gamma}$) cross section is important for developing theoretical nuclear reaction models and for applications. However, capture cross sections are difficult to calculate accurately and often must be measured.Purpose: We seek to confirm previous measurements and test cross-section calculations with an emphasis on the unresolved resonance region from 1 to 500 keV.Method: Cross sections were measured from 10 eV to 500 keV using the DANCE detector array at the LANSCE spallation neutron source. The measurements used a thin target, 48 mg/cm${}^{2}$ of depleted uranium. Gamma cascade spectra were also measured to provide an additional constraint on calculations. The data are compared to cross-section calculations using the code CoH${}_{3}$ and cascade spectra calculations made using the code dicebox.Results: This new cross-section measurement confirms the previous data. The measured gamma-ray spectra suggest the need for additional low-lying dipole strength in the radiative strength function. New Hauser-Feshbach calculations including this strength accurately predict the capture cross section without renormalization.Conclusions: The present cross-section data confirm previous measurements. Including additional low-lying dipole strength in the radiative strength function may lead to more accurate cross-section calculations in nuclei where $\ensuremath{\langle}{\ensuremath{\Gamma}}_{\ensuremath{\gamma}}\ensuremath{\rangle}$ has not been measured.