Collective modes associated with the proton-induced fission ofBi209

Gamma-ray multiplicity (first and second moments) has been measured in the 60 MeV proton-induced fission of ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$. From this work we have evidence that shell effects play an effective role at the scission point, even at an excitation energy of 65 MeV. Collective modes seem to be more easily excited when the nascent fragments are far from spherical shapes. The $\gamma$-multiplicity moments seem to depend weakly on excitation energy of the fissioning nucleus and do not really reflect the angular momentum of the entrance channel. The good agreement of our results with the Moretto-Schmitt model highly supports the role played by collective modes (bending) in the heavy ion induced fission and deep inelastic collisions which are presently the field of many recent experimental and theoretical investigations.