Towards improvement of the ²³⁸U level scheme using γ-spectroscopy of the (n, n’γ) reaction

Better knowledge of the neutron population in reactors is crucial to improve the accuracy of neutronics simulations of present day or future reactor cores. This population is partially driven by (n, xn) reactions. However, the cross sections of these reactions are not precisely known. This is particularly true for the 238U(n, n’γ) cross section, which is on the High Priority Request List. One method to measure this cross section is to use the prompt γ-ray spectroscopy coupled to time-of-flight measurements. This allows the total (n, n’) cross section to be inferred from the measured (n, xnγ) cross sections and the level scheme information. However, the knowledge of the 238U level scheme is still very incomplete, so an initiative to experimentally revisit the 238U structure has been launched using γ-γ coincidences spectroscopy. The v-Ball γ-spectrometer was coupled to the LICORNE directional neutron source of the ALTO facility, allowing study of inelastic scattering on 238U via γ-γ coincidences. The analysis of data obtained during the first v-Ball campaign was performed using the Radware escl8r software. At the present time, 73 γ-transitions and 50 levels registered in ENSDF have been confirmed and 120 new γ-transitions and 50 new levels have been found.