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Register a new userQuasi-elastic scattering in the 20Ne + 90,92Zr reactions: role of non-collective excitations
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Conventional coupled-channels analyses, that take account of only the collective excitations of the colliding nuclei, have failed to reproduce the different behavior of the experimental quasi-elastic barrier distributions for the $^{20}$Ne + $^{90,92}$Zr systems. To clarify the origins of this difference, we investigate the effect of non-collective excitations of the Zr isotopes. Describing these excitations in a random-matrix model, we explicitly take them into account in our coupled-channels calculations. The non-collective excitations are capable of reproducing the observed smearing of the peak structure in the barrier distribution for $^{20}$Ne + $^{92}$Zr, while not significantly altering the structure observed in the $^{20}$Ne + $^{90}$Zr system. The difference is essentially related to the closed neutron shell in $^{90}$Zr.
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The role played by the effective residual interaction in the transverse nuclear response for quasi-free electron scattering is discussed. The analysis is done by comparing different calculations performed in the Random--Phase Approximation and Ring Approximation frameworks. The importance of the exchange terms in this energy region is investigated and the changes on the nuclear responses due to the modification of the interaction are evaluated. The calculated quasi-elastic responses show clear indication of their sensibility to the details of the interaction and this imposes the necessity of a more careful study of the role of the different channels of the interaction in this excitation region.
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