GAMMA-RAY MULTIPLICITY MEASUREMENTS IN THE SI-28-64 REACTION AT 163.8-MEV(NI)

The Si-28 + Ni-64 reaction at 163.8 MeV incident energy is studied by measuring in coincidence gamma-rays and charged particles identified f rom Z=2 to Z=16. The transition from quasi-elastic to more damped reac tions is observed when the difference between the detected charge and the projectile one is increased. The strong influence of the particle decay on the measured gamma-ray multiplicity is evidenced with the hel p of the statistical model computer code CASCADE. Dissipative events a re well described in the rolling limit with excitation energy equally shared between the fragments. The overall agreement is lost for the fr agments with the projectile charge which show a small value of the gam ma-multiplicity even for dissipative events. This is probably connecte d with the previously observed non statistical behavior of gamma rays emitted in coincidence with projectile-like fragments. In the alpha-sp ectrum measured in coincidence with gamma-rays, the deexcitation of fu sed systems is clearly separated from in flight emission of deep inela stic fragments. The low measured gamma-ray multiplicity for fusion eve nts is qualitatively explained taking into account the effect of alpha -emission in the statistical decay.