Properties of the angular anisotropy of deep sub-barrier photofission of even-even nuclei

We report the method and results of measurements of angular distributions of fragments in the (..gamma..,f) reaction for /sup 232/Th, /sup 236/U, and /sup 238/U carried out in connection with the investigation of the properties of deep sub-barrier photofission: the isomeric shelf phenomenon, disappearance of the angular anisotropy (/sup 236,238/U), and the absence of this effect and of the sub-barrier enhancement of quadrupole photofission in /sup 232/Th. The experimental data presented permit an understanding of the nature and relation of these properties in terms of the concept of a two-humped fission-barrier structure.