Independent yields of 80Br, 82Br, 128I, and 130I from the thermal neutron fission of 235U, 239Pu, 233U, and 238Np

Absolute independent yields of the shielded nuclides 80Br, 82Br, 128I, and 130I produced in the thermal neutron fission of 235U, 239Pu, and 233U have been determined by careful mass spectrometric analyses of krypton and xenon fission products. In addition, a fractional independent yield of 130I from the thermal neutron fission of 238Np has been determined, and an upper limit has been set for the independent yield of 126I from 235U fission. All the yields from 235U fission except that of 128I are consistent with the Gaussian charge distribution described by Wahl. However, conventional theories of charge distribution in fission do not account for the irregular variation in iodine yields from one fissile nuclide to another. A mechanism based on differences in neutron emission probabilities from prompt fission fragments is proposed in order to explain this variation.