Absorption cross-section measurements for 252Cf spontaneous fission neutrons

Absolute absorption cross sections of 232Th and 197Au for 252Cf spontaneous fission neutrons have been measured. Irradiations were performed in an exceptionally low mass source-foil arrangement, providing a "pure" spectrum with few corrections. Calibration of the activation detector was achieved by irradiating identical foils in the Standard Thermal Flux at the National Bureau of Standards. The results obtained were 79.9 ± 2.9 mb for 197Au and 87.8 ± 4.0 mb for 232Th. The corresponding values calculated from ENDF/B-III data are 84.3 and 99.3 mb, respectively.A simple ratio technique was also used to obtain an independent estimate of the relative 232Th to 197Au integral cross sections, yielding a value in good agreement with that above. This technique was extended to 181Ta, 98Mo, and 63Cu.