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Register a new userOscillations above the barrier in the fusion of 28Si + 28Si
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Fusion cross sections of 28Si + 28Si have been measured in a range above the barrier with a very small energy step (DeltaElab = 0.5 MeV). Regular oscillations have been observed, best evidenced in the first derivative of the energy-weighted excitation function. For the first time, quite different behaviors (the appearance of oscillations and the trend of sub-barrier cross sections) have been reproduced within the same theoretical frame, i.e., the coupled-channel model using the shallow M3Y+repulsion potential. The calculations suggest that channel couplings play an important role in the appearance of the oscillations, and that the simple relation between a peak in the derivative of the energy-weighted cross section and the height of a centrifugal barrier is lost, and so is the interpretation of the second derivative of the excitation function as a barrier distribution for this system, at energies above the Coulomb barrier.
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The cross sections of complete fusion and incomplete fusion for the $ ^{9} $Be + $ ^{197} $Au system, at energies not too much above the Coulomb barrier, were measured for the first time. The online activation followed by offline $gamma$-ray spectroscopy method was used for the derivation of the cross sections. A slightly higher value of ICF/TF ratio has been observed, compared to other systems reported in the literature with $ ^{9} $Be beam. The experimental data were compared with coupled channel calculations without taking into account the coupling of the breakup channel, and experimental data of other reaction systems with weakly bound projectiles. A complete fusion suppression of about 40% was found for the $ ^{9} $Be + $ ^{197} $Au system, at energies above the barrier, whereas the total fusion cross sections are in agreement with the calculations.
Above-barrier fusion cross-sections for an isotopic chain of oxygen isotopes with A=16-19 incident on a $^{12}$C target are presented. Experimental data are compared with both static and dynamical microscopic calculations. These calculations are unable to explain the $sim$37% increase in the average above-barrier fusion cross-section observed for $^{19}$O as compared to $beta$-stable oxygen isotopes. This result suggests that for neutron-rich nuclei existing time-dependent Hartree-Fock calculations underpredict the role of dynamics at near-barrier energies. High-quality measurement of above-barrier fusion for an isotopic chain of increasingly neutron-rich nuclei provides an effective means to probe this fusion dynamics.
The possible occurence of highly deformed configurations in the $^{40}$Ca di-nuclear system formed in the $^{28}$Si + $^{12}$C reaction is investigated by analyzing the spectra of emitted light charged particles. Both inclusive and exclusive measurements of the heavy fragments (A $geq$ 10) and their associated light charged particles (protons and $alpha$ particles) have been made at the IReS Strasbourg {sc VIVITRON} Tandem facility at bombarding energies of $E_{lab}$ ($^{28}$Si) = 112 MeV and 180 MeV by using the {sc ICARE} charged particle multidetector array. The energy spectra, velocity distributions, in-plane and out-of-plane angular correlations of light charged particles are compared to statistical-model calculations using a consistent set of parameters with spin-dependent level densities. This spin dependence approach suggests the onset of large nuclear deformation in $^{40}$Ca at high spin. This conclusion might be connected with the recent observation of superdeformed bands in the $^{40}$Ca nucleus. The analysis of $alpha$ particles in coincidence with $^{32}$S fragments suggests a surprisingly strong $^{8}$Be cluster emission of a binary nature.
Fusion excitation function of $^{35}$Cl + $^{130}$Te system is measured in the energy range around the Coulomb barrier and analyzed in the framework of the coupled-channels approach. The role of projectile deformation, nuclear structure, and the couplings of inelastic excitations and positive Q$-$value neutron transfer channels in sub-barrier fusion are investigated through the comparison of reduced fusion excitation functions of $^{35,37}$Cl +$^{130}$Te systems. The reduced fusion excitation function of $^{35}$Cl + $^{130}$Te system shows substantial enhancement over $^{37}$Cl + $^{130}$Te system in sub-barrier energy region which is attributed to the presence of positive Q-value neutron transfer channels in $^{35}$Cl + $^{130}$Te system. Findings of this work strongly suggest the importance of +2$n$ - transfer coupling in sub-barrier fusion apart from the simple inclusion of inelastic excitations of interacting partners, and are in stark contrast with the results presented by Kohley textit{et al.}, [Phys. Rev. Lett. 107, 202701 (2011)].
The 12C+16O resonant radiative capture reaction has been studied at 5 bombarding energies between Elab = 15.4 and 21.4 MeV, around the Coulomb barrier, at the Triumf laboratory (Vancouver, Canada) using the Dragon 0{deg} spectrometer and the associated BGO array. The most remarquable result is the previously unobserved decay path through 28Si doorway states of energies around 12 MeV leading to the measurement of new capture cross-sections. The feeding of specific, deformed states in 28Si from the resonances is discussed, as well as the selective feeding of 1^+ T=1 states around 11 MeV.
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