Thermal Neutron Cross-Section Measurements of U²³³, U²³⁵, Pu²⁴⁰, U²³⁴, and I¹²⁹ with the ORNL Fast Chopper Time-of-Flight Neutron Spectrometer

The neutron total cross sections of U²³³, U²³⁵, Pu²⁴⁰, U²³⁴, and I¹²⁹ were measured with the new ORNL fast chopper time-of-flight neutron spectrometer over an energy range from approximately O.02 to O.20 ev. The cross section data have been fitted in the energy range from approximately O.02 to O.04 ev by the least squares method to the following equation: where σ_T and σ_sc are the total and scattering cross sections, E is the neutron energy, and a and b are the coefficients of fit. From this least squares fit, the 2200 m/sec neutron total cross sections of U²³³, U²³⁵, Pu²⁴⁰, U²³⁴, and I¹²⁹ were determined to be 587 ± 3, 693 ± 5, 290 ± 8, 110 ± 4, and 35 ± 4 barns, respectively. A brief description of the new ORNL fast chopper time-of-flight neutron spectrometer is included in this paper.