arXiv subjects

Sl. Cavallaro

Publications and source records attributed to Sl. Cavallaro.

6 recordsLinked to original sources

arXiv1999

Vanishing spin alignment : experimental indication of triaxial $\bf ^{28}Si + {^{28}Si}$ nuclear molecule

Fragment-fragment-$γ$ coincidences have been measured for $\rm ^{28}Si + {^{28}Si}$ at an energy corresponding to the population of a conjectured resonance in $^{56}$Ni. Fragment angular distributions as well as $γ$-ray angular correlations indicate that the spin orientations of the outgoing fragments are perpendicular to the orbital angular momentum. This differs from the $\rm ^{24}Mg+{^{24}Mg}$ and the $\rm ^{12}C+{^{12}C}$ resonances, and suggests two oblate $\rm ^{28}Si$ nuclei interacting in an equator-to-equator molecular configuration.

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arXiv1998

Study of the Fusion-Fission Process in the $^{35}Cl+^{24}Mg$ Reaction

Fusion-fission and fully energy-damped binary processes of the $^{35}$Cl+$^{24}$Mg reaction were investigated using particle-particle coincidence techniques at a $^{35}$Cl bombarding energy of E$_{lab}$ $\approx$ 8 MeV/nucleon. Inclusive data were also taken in order to determine the partial wave distribution of the fusion process. The fragment-fragment correlation data show that the majority of events arises from a binary-decay process with a relatively large multiplicity of secondary light-charged particles emitted by the two primary excited fragments in the exit channel. No evidence is observed for ternary-breakup processes, as expected from the systematics recently established for incident energies below 15 MeV/nucleon and for a large number of reactions. The binary-process results are compared with predictions of statistical-model calculations. The calculations were performed using the Extended Hauser-Feshbach method, based on the available phase space at the scission point of the compound nucleus. This new method uses temperature-dependent level densities and its predictions are in good agreement with the presented experimental data, thus consistent with the fusion-fission origin of the binary fully-damped yields.

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arXiv1998

Spin-Alignment and Quasi-Molecular Resonances in Heavy-Ion Collision

Fragment-fragment-$γ$ triple coincidence measurements of the $^{28}$Si~$+$~$^{28}$Si reaction at E$_{\rm c.m.}$~=~55.8 MeV, carefully chosen to populate a well known quasi-molecular resonance in $^{56}$Ni, have been performed at the VIVITRON tandem facility by using the Eurogam Phase~II $γ$-ray spectrometer. In the $^{28}$Si~$+$~$^{28}$Si reaction, the resonant behavior of the $^{28}$Si $+$ $^{28}$Si exit-channel is clearly observed by the present fragment-fragment coincidence data. The more unexpected result is the spin disalignment of the $^{28}$Si $+$ $^{28}$Si resonance. This has been demonstrated first by the measured angular distributions of the elastic 0$^{+}$, inelastic 2$^{+}$ and mutual excitation channels 2$^{+}-2^{+}$, which are dominated by a unique and pure partial wave with L = 38 ${\rm \hbar}$, and has been confirmed by measuring their particle-$γ$ angular correlations with Eurogam Phase II. The spin disalignment supports new molecular model predictions, in which the observed resonance would correspond to the ''Butterfly mode''. A discussion concerning the {\it spin alignment and spin disalignment} for different systems : $^{12}$C~$+$~$^{12}$C, $^{24}$Mg~$+$~$^{24}$Mg and $^{28}$Si~$+$~$^{28}$Si will be given.}

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arXiv1997

Fusion and Binary-Decay Mechanisms in the $^{35}$Cl+$^{24}$Mg System at E/A $\approx$ 8 MeV/Nucleon

Compound-nucleus fusion and binary-reaction mechanisms have been investigated for the $^{35}$Cl+$^{24}$Mg system at an incident beam energy of E$_{Lab}$= 282 MeV. Charge distributions, inclusive energy spectra, and angular distributions have been obtained for the evaporation residues and the binary fragments. Angle-integrated cross sections have been determined for evaporation residues from both the complete and incomplete fusion mechanisms. Energy spectra for binary fragment channels near to the entrance-channel mass partition are characterized by an inelastic contribution that is in addition to a fully energy damped component. The fully damped component which is observed in all the binary mass channels can be associated with decay times that are comparable to, or longer than the rotation period. The observed mass-dependent cross sections for the fully damped component are well reproduced by the fission transition-state model, suggesting a fusion followed by fission origin. The present data cannot, however, rule out the possibility that a long-lived orbiting mechanism accounts for part or all of this yield.

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arXiv1997

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

Fragment-fragment-$γ$ 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 $γ$-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-$γ$ angular correlations and supported by the molecular model prediction of a "butterfly motion". The K$^π$ = 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 $γ$-ray transition $0^{+} (8507.8 keV) \to 2^{+}_{1} (2230.2 keV) $.

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arXiv1996

Statistical Binary Decay of $^{35}$Cl + $^{24}$Mg at 8 MeV/nucleon

The properties of the two-body channels in the $^{35}$Cl + $^{24}$Mg reaction at a bombarding energy of 275 MeV have been investigated by using fragment-fragment coincident techniques. The exclusive data show that the majority of events arises from a binary-decay process. The rather large number of secondary light charged-particles emitted from the two excited exit fragments are cnsistent with the expectations of the Extended Hauser-Feshbach Method. No evidence for the occurence of ternary break-up events is observed.

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