Energy and Angular Distribution of Alpha Particles Emitted in Thermal-Neutron Fission ofU235

The energy and angular distributions of $\alpha$ particles emitted in thermal-neutron fission of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$ have been studied in a three-parameter correlation experiment for $\alpha$ angles between 50 and 130°. These distributions are compared with the results of trajectory calculations to get a "best fit" set of initial scission conditions. The derived initial fragment separation of 24 fm and initial average kinetic energy of 31 MeV are in good agreement with liquid-drop calculations, while the initial most probable $\alpha$ energy was found to be 3.4 MeV. The results indicate a shift in the scission point of 1-2 fm towards the light fragment, for a variation in mass ratio between 1.1 and 2. The effect of $\alpha$ recoil on the experimental distributions is discussed in detail.