Angular correlation of fission fragments and prompt γ rays from spontaneous fission of Cf252

The angular correlation of fission fragments and prompt γ rays in spontaneous fission of Cf252 has been measured for forward and backward angles for γ-ray energies greater than 0.3 MeV. The time-of-flight method has been used to eliminate the fission neutrons, and the measurements have been performed with the source on a thick backing and for two geometries, i.e. with the semiconductor detector and the NaI(Tl) scintillation detector on opposite sides of the source and with the detectors on the same side of the source. A forward-backward anisotropy in the laboratory system has been established. A minimum observed at about right angles in both geometries is significantly larger in the latter geometry. The results can fairly well be accounted for by the assumption that essentially all the γ rays are emitted after the fragments have stopped in the backing, and that the angulat distribution in the centre-of-mass system is of the type predicted by the statistical model with an anisotropy of −11%.