Neutron Total Cross Sections of ¹⁸¹Ta and ²³⁸U from 24.3 keV to 1 MeV and Average Resonance Parameters

The neutron total cross sections of ¹⁸¹Ta and ²³⁸U have been obtained in the energy range from 24.3 keV to 1 MeV by means of neutron transmission measurements using the Japan Atomic Energy Research Institute Linac, The measurements were carried out with the iron-filtered neutron beam technique and the time-of-flight method, using an NE-110 plastic scintillator as a neutron detector at a 100-m station. For ²³⁸U, correction for the resonance self-shielding effect was taken into account below 270 keV by measuring the transmission of four samples of different thicknesses. By fitting average R matrix calculations to the observed total cross sections, the neutron strength functions S_ℓ for p and d waves, and distant level parameters for s, p, and d waves were deduced to be: , and for ¹⁸¹Ta, and , and for ²³⁸U. The effective s-wave scattering radii were 7.90 ± 0.03 and 9.30 ± 0.04 fm for ¹⁸¹Ta and ²³⁸U, respectively.