Angular Distribution of Fragments from Neutron-Induced Fission

Abstract

A parallel plate ionization chamber, in which one electrode served as a collimator, was employed to study the angular distribution of fission fragments referred to the neutron beam axis. Fragments from neutron bombardment of the following nuclei were examined: ${\mathrm{Th}}^{232}$, ${\mathrm{U}}^{233}$, ${\mathrm{U}}^{235}$, ${\mathrm{U}}^{238}$, and ${\mathrm{Np}}^{237}$. When 14-Mev neutrons were used, a preponderance of fission along the neutron axis as compared with the orthogonal direction was noted. The average value obtained for the $\frac{0\ifmmode^\circ\else\textdegree\fi{}}{90\ifmmode^\circ\else\textdegree\fi{}}$ ratios was 1.26. Thermal neutron fission was found to be isotropic.