Cross section and.gamma-ray spectra for U-238(n,gamma) measured with the DANCE detector array at the Los Alamos Neutron Science Center
Abstract
Background: Accurate knowledge of the U-238(n,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 CoH3 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 Gamma gamma has not been measured.