Absorption Cross-Section Measurements for Californium-252 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.