Measurement of dynamical dipole gamma -ray emission in the N/Z -asymmetric fusion reaction O 16 + Sn 116 at 12 MeV/nucleon

A new measurement of the dynamical dipole emission was performed in the system 16O + 116Sn at 12 MeV/nucleon. These data, together with those measured at 8.1 MeV/nucleon and 15.6 MeV/nucleon on the same system, provide the dependence of the dynamical dipole total emission yield on the beam energy. The energy removed by preequilibrium charged particles emission was directly measured and this made possible the direct estimation of the compound nucleus excitation energy. The experimental results show a weak increase of the dynamical dipole total yield with beam energy and they are in agreement both in trend and in absolute values with the predictions of the theoretical model based on the Boltzmann-Nordheim-Vlasov approach. The measured γ -ray angular distribution has a dipole character but with a strong quenching probably owing to the rotation of the dipolar axis during the fusion and thermalization processes.