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A. M. Moro

Publications and source records attributed to A. M. Moro.

66 records · Page 4Linked to original sources

Transfer to the continuum and Breakup reactions

Reaction theory is an essential ingredient when performing studies of nuclei far from stability. One approach for the calculation of breakup reactions of exotic nuclei into two fragments is to consider inelastic excitations into the single particle continuum of the projectile. Alternatively one can also consider the transfer to the continuum of a system composed of the light fragment and the target. In this work we make a comparative study of the two approaches, underline the different inputs, and identify the advantages and disadvantages of each approach. Our test cases consist of the breakup of $^{11}$Be on a proton target at intermediate energies, and the breakup of $^8$B on $^{58}$Ni at energies around the Coulomb barrier. We find that, in practice the results obtained in both schemes are in semiquantitative agreement. We suggest a simple condition that can select between the two approaches.

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Long range absorption in the scattering of 6He on 208Pb and 197Au at 27 MeV

Quasi-elastic scattering of 6He at E_lab=27 MeV from 197Au has been measured in the angular range of 6-72 degrees in the laboratory system employing LEDA and LAMP detection systems. These data, along with previously analysed data of 6He + 208Pb at the same energy, are analyzed using Optical Model calculations. The role of Coulomb dipole polarizability has been investigated. Large imaginary diffuseness parameters are required to fit the data. This result is an evidence for long range absorption mechanisms in 6He induced reactions.

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Three-body continuum discretization in a basis of transformed harmonic oscillator states

The inclusion of the continuum in the study of weakly-bound three-body systems is discussed. A transformed harmonic oscillator basis is introduced to provide an appropriate discrete and finite basis for treating the continuum part of the spectrum. As examples of the application of the method the strength functions corresponding to several operators that couple the ground state to the continuum are investigated, for 6He, and compared with previous calculations. It is found that the energy moments of these distributions are accurately reproduced with a small basis set.

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Understanding low energy reaction with exotic nuclei

Recent developments on the understanding of low energy reactions are highlighted. Emphasis is given to the CDCC framework where the breakup channels of the projectile are included explicitly. Properties of the breakup couplings are presented. Comments are given with regard to the separation between the nuclear and the Coulomb contributions to breakup cross sections as well as the dependence on the optical potentials. A discussion on the sensitivity of the CDCC basis is discussed, by comparing pure breakup results with transfer to the continuum calculations. Finally, some remaining controversies show the need to go beyond the single particle picture for the projectile.

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Progress on reactions with exotic nuclei

Modelling breakup reactions with exotic nuclei represents a challenge in several ways. The CDCC method (continuum discretized coupled channel) has been very successful in its various applications. Here, we briefly mention a few developments that have contributed to the progress in this field as well as some pertinent problems that remain to be answered.

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Higher order effects in the $^{16}O(d,p)^{17}O$ and $^{16}O(d,n)^{17}F$ transfer reactions

Full Coupled Channels Calculations were performed for the $^{16}O(d,n)^{17}F$ and $^{16}O(d,p)^{17}O$ transfer reactions at several deuteron incident energies from $E_{lab}=2.29$ MeV up to 3.27 MeV. A strong polarization effect between the entrance channel and the transfer channels $^{16}O(d,n)^{17}F(1/2^{+},0.495)$ and $^{16}O(d,p)^{17}O(1/2^{+},0.87)$ was observed. This polarization effect had to be taken into account in order to obtain realistic spectroscopic factors from these reactions.

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Uncorrelated scattering approximation revisited

The formalism to describe the scattering of a weakly bound projectile nucleus by a heavy target is investigated, using the Uncorrelated Scattering Approximation. The main assumption involved is to neglect the correlation between the fragments of the projectile in the region where the interaction with the target is important. It is shown that the angular momentum of each fragment with respect to the target is conserved. Moreover, when suitable approximations are assumed, the kinetic energy of each fragment is also shown to be conserved. The S-matrix for the scattering of the composite system can be written as a combination of terms, each one being proportional to the product of the S-matrices of the fragments.

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Disentangling the transfer and breakup contributions from the inclusive 8Li+ 208Pb reaction

An analysis of the elastic and one-neutron removal channel for the reaction 8Li+208Pb reaction at energies around the Coulomb barrier is presented. For the elastic scattering, an optical model analysis of the experimental data is performed. The observed 7Li is interpreted as the superposition of the one-neutron transfer reaction, 208Pb(8Li,7Li)209Pb, and the breakup reaction. The separate contribution of each one of these processes has been calculated within the DWBA formalism. The sum of both contributions explains adequately the experimental angular distribution of 7Li.

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Continuum effects in reactions involving weakly bound nuclei

The relevance of the continuum effects in transfer reactions is discussed in conection with the determination of observables of astrophysical interest. In particular, we examine the validity of the Distorted Wave Born Approximation (DWBA) as a tool to extract the astrophysical \emph{(S_{17}(0))} factor. For this purpose, we present calculations for the reaction (^{14})N((^{7} )Be,(^{8})B)(^{13})C comparing the DWBA method with the more sophysticated CDCC-Born approximation

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(^{8})B breakup in elastic and transfer reactions

We have studied the transfer reaction $^{14}$N($^7$Be,$^8$B)$^{13}$C at (\mathrm{E}_{\mathrm{lab}}=84) MeV, paying special attention to the effects of the coupling to the continuum in the exit channel. Using the Continuum Discretized Coupled Channels (CDCC) formalism, we find that these effects are important for the description of the elastic scattering observables. However, for the transfer process, differences between the predictions of the differential cross section within the Distorted Wave Born Approximation (DWBA) and the CDCC-Born approximation (CDCC-BA) are found to be negligible. This result supports the use of the DWBA method as a reliable tool to extract the $S_{17}(0)$ factor in this case.

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Tensor representation of the nucleon-nucleon amplitude

Many approaches to nucleon-nucleus elastic and inelastic scattering are based on the use of the free-space nucleon-nucleon transition amplitude. In calculations where the full spin-dependence of this amplitude is needed, its use is more tractable when it is expressed in terms of irreducible tensor operators of the spins of the interacting nucleons. We present general formulae for this representation which is particularly useful for inelastic scattering studies involving spin-flip transitions of a target nucleon.

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Uncorrelated scattering approximation for the scattering and break-up of weakly bound nuclei on heavy targets

The scattering of a weakly bound (halo) projectile nucleus by a heavy target nucleus is investigated. A new approach, called the Uncorrelated Scattering Approximation, is proposed. The main approximation involved is to neglect the correlation between the fragments of the projectile in the region where the interaction with the target is important. The formalism makes use of hyper-spherical harmonics, Raynal-Revay coefficients and momentum-localized wave functions to expand projectile channel wave functions in terms of products of the channel wave function of the individual fragments. Within this approach, the kinetic energy and angular momentum of each fragment is conserved during the scattering process. The elastic, inelastic and break-up S-matrices are obtained as an analytic combination involving the bound wave function of the projectile and the product of the S-matrices of the fragments. The approach is applied to describe the scattering of deuteron on $^{58}$Ni at several energies. The results are compared with experimental data and continuum-discretized coupled-channels calculations.

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