Mass dependence of fragment angular distributions in the fission of ²³²Th and ²³⁶U induced by polarized photons

Abstract

Near-barrier fission of ²³²Th and ²³⁶U induced by linearly polarized photons has been investigated. The experiments have been carried out at the “off-axis” bremsstrahlung facility of the Giessen 65 MeV electron linac. Fragment angular, mass and energy distributions have been measured simultaneously allowing the investigation of correlations between these fragment characteristics. A consistent assignment of the quantum numbers J^π and K for the fussion channels involved in the fission process is proposed. For the first time, the polar anisotropies and azimuthal asymmetries of the fission fragment angular distributions W(θ, φ) have been investigated as a function of the fragment masses. The results are discussed in the framework of the double-humped fission barrier concept and the so-called “multi-exit fission channel” model. Additionally, angular distributions of heavy and light fission fragments from photofission of ²³⁶U have been analyzed for a possible asymmetry with respect to θ = 90°.