Subthreshold photofission of even-even nuclei

Within quantum-mechanical fission theory, the angular distributions of fragments originating from the subthreshold photofission of the even-even nuclei {sup 232}Th, {sup 234}U, {sup 236}U, {sup 238}U, {sup 238}Pu, {sup 240}Pu, and {sup 242}Pu are analyzed for photon energies below 7 MeV. Special features of various fission channels are assessed under the assumption that the fission barrier has a two-humped shape. It is shown that the maximum value of the relative orbital angular momentum L{sub m} of fission fragments can be found upon taking into account deviations from the predictions of A. Bohr's formula for the angular distributions of fission fragments. The result is L{sub m} {approx_equal} 30. The existence of an 'isomeric shelf' for the angular distributions of fragments from {sup 236}U and {sup 238}U photofission in the low-energy region is confirmed.