Resonance Parameters of Tantalum-181 in Neutron Energy Range from 100 to 4,300eV

Neutron transmission measurements were performed on natural tantalum (abundance ratio 99.988% for 181Ta) in the energy range of 100–4,300 eV using the Japan Atomic Energy Research Institute linac. The transmissions were measured using 55 and 190 m time-of-flight spectrometers for two and three samples of different thicknesses, respectively. These transmission data were simultaneously analyzed with a least squares fitting program based on a multl-level Breit-Wigner formula, and resonance energies and neutron width were obtained for 696 resonances of 181Ta. The statistical analysis of these parameters gave the s-wave average level spacing of D=4.10±0.14 eV and s-wave neutron strength functions of (1.67±0.13) × 10−4, (1.09 ± 0.09) × 10−4 and (1.42 ± 0.20) × 10−4 for the energy intervals from 100 − 1,700 eV, 1,700–3,400 eV and 3,400–4,300 eV, respectively. This significant difference among the neutron strength function for each energy interval is a prominent result of the present experiments and is of great interest.