Fission Fragment Spectroscopy on a $^{28}$Si+$^{28}$Si Quasimolecular Resonance

Abstract

Fragment-fragment-$\gamma$ triple coincident measurements of the $^{28}$Si + $^{28}$Si reaction at E$_{lab.}$ = 111.6 MeV carefully chosen to populate J = 38$^{+}$ resonance have been performed at the VIVITRON tandem facility by using Eurogam Phase II $\gamma$-ray spectrometer. In the $^{28}$Si + $^{28}$Si exit-channel, the resonance behavior of the $^{28}$Si + $^{28}$Si reaction at the beam energy is clearly confirmed. An unexpected spin disalignment has been observed in the measured angular distributions in the elastic, inelastic, and mutual excitation channels. This disalignment is found to be consistent with particle-$\gamma$ angular correlations and supported by the molecular model prediction of a "butterfly motion". The K$^{\pi}$ = 0$^{+}_{3}$ band corresponding to the large prolate deformation of the $^{28}$Si is more intensely fed in the resonance region. The selective population of high-excited states are discussed within a statistical fusion-fission model. In the $^{32}$S + $^{24}$Mg exit-channel, the spectroscopic study of the $^{32}$S, has revealed the contribution of a new $\gamma$-ray transition $0^{+} (8507.8 keV) \to 2^{+}_{1} (2230.2 keV) $.