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 232Th, 234U, 236U, 238U, 238Pu, 240Pu, and 242Pu 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 Lm 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 Lm ≈ 30. The existence of an “isomeric shelf” for the angular distributions of fragments from 236U and 238U photofission in the low-energy region is confirmed. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]