Absolute Radiative Capture Cross Section for Fast Neutrons in ²³⁸U

The capture cross section of ²³⁸U has been measured absolutely at a neutron energy of 30 keV using kinematically collimated neutrons from the ⁷Li(p, n) ⁷Be reaction near threshold. Activation techniques were used to determine both the number of capture events and the number of neutrons that occurred during the irradiation. The result of the ²³⁸U capture cross section measurement is 479 ± 14 mb at 30 keV. In addition, the shape of the ²³⁸ U capture cross section has been measured for neutron energies from 25 to 500 keV using neutrons from the ⁷Li(p, n)⁷ Be reaction. The capture reactions in the ²³⁸ U target were detected using a large liquid scintillator tank and time-of-flight techniques. The relative neutron flux was measured using a flat response neutron detector. The cross-section shape measurement was normalized to the present absolute measurement at 30 keV. The present measurement has been compared with several measured values, theoretical calculations, and compiled values of the ²³⁸U capture cross section as given by other authors.