Subcadmium in-Pile Etas and Absorption Cross Sections of U²³³, Pu²³⁹, and Pu²⁴¹

Measurements of two independent types have been made of the reactivity effect in a thermal test reactor of samples of U²³⁵, U²³³, Pu²³⁹, and Pu²⁴¹. From these measurements average subcadmium values of eta () relative to of U²³⁵ are obtained independently of other knowledge of the average absorption cross sections. Average absorption cross sections are also obtained from the measurements. Values of () for U²³³, Pu²³⁹, and Pu²⁴¹ are respectively 2.231 ± 0.034, 1.927 0.024, and 2.213 ± 0.07. The corresponding value of η (0.0253 ev) of Pu²³⁹ is found to be 2.025. A presentation of the method and results are given together with a comparison with previous work.