Fission of Ag and Br in Nuclear Emulsion by 1.0-3.0-Bev Protons

A study was made of the fission stars produced in low sensitivity nuclear emulsions by 1.0-3.0 Bev protons. These events are characterized by two densely ionizing tracks in approximately opposite directions. The fractions of the inelastic cross section of Ag and Br leading to fission at 1.0, 2.0, and 3.0 Bev are 0.03, 0.06, and 0.11, respectively. Symmetric fission is most probable: in 41% of the events the ratio of track lengths is 1.0-1.5; in 27% the ratio is 1.5-2.0. The fission fragment velocity distribution (mean of $0.044c$) was derived from the range distribution (mean of 9 μ). The average angle between the fission fragments deviates from $\pi$ by 42°, indicating that the center-of-mass system is moving at a mean velocity of $0.016c$ approximately along the line bisecting the angle between the fragments. From a study of the energy spectrum of the alpha particles and of their angular distribution with respect to the fission fragments it appears that about 75% of the alphas are emitted prior to fission and about 25% simultaneously with fission.