Angular Distribution of Fission Fragments from 22-Mev Proton-Induced Fission ofU238,U235,U233,Th232, andTh230

Abstract

Angular distributions of several fission fragments from 22-Mev proton-induced fission of ${\mathrm{U}}^{238}$, ${\mathrm{U}}^{235}$, ${\mathrm{U}}^{233}$, ${\mathrm{Th}}^{232}$, and ${\mathrm{Th}}^{230}$ were measured. The data are fitted to $N\left(\theta \right)=a+b{cos}^2\theta$ where $b$ ranges from $0.08a$ to $0.28a$. The coefficients for possible "$cos\theta$" terms (i.e., terms asymmetric about 90 deg) are no larger than $0.01a$. In every case, asymmetric fission gives more anisotropic angular distributions than symmetric fission. The anisotropy in symmetric fission is about the same for all target elements; in asymmetric fission, the thorium isotopes have larger anisotropies than the uranium isotopes. Among the latter, the anisotropies are quite similar for ${\mathrm{U}}^{238}$ and ${\mathrm{U}}^{235}$, but somewhat smaller for ${\mathrm{U}}^{233}$. Explanations for various aspects of the phenomena are proposed.