Angular Dependence of Coincidences between Fission Neutrons

Abstract

Coincidences between the neutrons from neutron-induced fission of ${\mathrm{U}}^{235}$ were measured using fast neutron counters, working on the principle of proton recoil. From measurements at angles of 30°, 60°, 90°, 135°, and 180° between the directions of the fission neutrons, it was found that the number of coincidences is fairly constant from 30° to 90°, and increases by about a factor 2 from 90° to 180°. This result can be explained if it is assumed that the fission neutrons most probably come from opposite fragments.