Ternary Fission of Uranium-236* and -234

Abstract

A detailed study of the ternary fission of ${\mathrm{U}}^{236*}$ and ${\mathrm{U}}^{234*}$ has been completed using a triple-coincidence technique and a three-parameter energy measurement on the product fragments. Arguments based on experimental energy, angular, and frequency correlations are presented for elimination of phenomena other than ternary fission as explanations of the observed data. Among possible interfering effects considered were (1) accidental events, (2) instrumental malfunctions, and (3) scattering phenomena. In connection with the third factor, an experimental determination of the characteristics of binary-fission-fragment scattering confirmed the absence of this phenomenon from all but one of the angular arrangements investigated. It is concluded that the major portion of triple events observed arises from a ternary-fission process. A difference in the ternary-fission properties of ${\mathrm{U}}^{236*}$ and ${\mathrm{U}}^{234*}$ is interpreted as caused by the dominant effect of underlying shell structure in forming the product fragments, an effect which may result in the formation of unique (preselected) fragments masses. Mass distributions indicate the formation of low-mass fission products with mass peaks centered near 30 and 50 amu. A qualitative mechanism by which the ternary-fission process may occur is presented.