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Elastic Scattering, Fusion, and Breakup of Light Exotic Nuclei

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Elastic Scattering, Fusion, and Breakup of Light Exotic Nuclei Eur. Phys. J. A (2016) 52: 123 THE EUROPEAN DOI 10.1140/epja/i2016-16123-1 PHYSICAL JOURNAL A Review Elastic scattering, fusion, and breakup of light exotic nuclei J.J. Kolata1,a, V. Guimar˜aes2, and E.F. Aguilera3 1 Physics Department, University of Notre Dame, Notre Dame, IN, 46556-5670, USA 2 Instituto de F`ısica,Universidade de S˜aoPaulo, Rua do Mat˜ao,1371, 05508-090, S˜aoPaulo, SP, Brazil 3 Departamento de Aceleradores, Instituto Nacional de Investigaciones Nucleares, Apartado Postal 18-1027, C´odigoPostal 11801, M´exico, Distrito Federal, Mexico Received: 18 February 2016 Published online: 10 May 2016 c The Author(s) 2016. This article is published with open access at Springerlink.com Communicated by N. Alamanos Abstract. The present status of fusion reactions involving light (A<20) radioactive projectiles at energies around the Coulomb barrier (E<10 MeV per nucleon) is reviewed, emphasizing measurements made within the last decade. Data on elastic scattering (providing total reaction cross section information) and breakup channels for the involved systems, demonstrating the relationship between these and the fusion channel, are also reviewed. Similarities and differences in the behavior of fusion and total reaction cross section data concerning halo nuclei, weakly-bound but less exotic projectiles, and strongly-bound systems are discussed. One difference in the behavior of fusion excitation functions near the Coulomb barrier seems to emerge between neutron-halo and proton-halo systems. The role of charge has been investigated by comparing the fusion excitation functions, properly scaled, for different neutron- and proton-rich systems. Possible physical explanations for the observed differences are also reviewed. Contents 9.2 Breakup of 11Be................. 22 9.3 Fusion of 11Be.................. 22 1 Introduction....................... 1 10 Reactions with 8B ................... 23 2Reactionswith6He................... 2 10.1 Elastic scattering of 8B ............. 23 2.1 Elastic scattering of 6He............. 2 10.2 Breakup of 8B .................. 24 2.2 Breakup of 6He.................. 4 10.3 Fusion of 8B.................... 25 2.3 Fusion of 6He................... 5 11 Reactions with 10C................... 26 3Reactionswith8He................... 7 11.1 Elastic scattering of 10C............. 27 4Reactionswith8Li................... 8 11.2 Fusion of 10C ................... 27 4.1 Elastic scattering of 8Li............. 8 12 Reactions with 11C................... 27 4.2 Transfer reactions induced by 8Li........ 9 12.1 Elastic scattering of 11C............. 27 14 4.3 Fusion of 8Li................... 9 13 Reactions with C................... 28 14 5Reactionswith9Li................... 10 13.1 Elastic scattering of C............. 28 14 5.1 Elastic scattering of 9Li............. 10 13.2 Transfer reactions with C ........... 28 14 5.2 Fusion of 9Li................... 10 13.3 Fusion of C ................... 29 15 6Reactionswith11Li................... 11 14 Reactions with C................... 30 15 6.1Elasticscattering................. 11 14.1 Elastic scattering of C............. 30 15 6.2 Breakup of 11Li.................. 13 14.2 Fusion of C ................... 30 12 6.3 Fusion of 11Li................... 13 15 Reactions with N................... 30 13 7Reactionswith7Be................... 14 16 Reactions with N................... 31 17 7.1 Elastic scattering of 7Be............. 14 17 Reactions with F................... 31 17 7.2 Breakup of 7Be.................. 16 17.1 Elastic scattering of F ............. 31 17 7.3 Fusion of 7Be................... 17 17.2 Breakup of F .................. 34 17 8Reactionswith10Be.................. 17 17.3 Fusion of F ................... 35 8.1 Elastic scattering of 10Be............ 18 8.2 Fusion of 10Be.................. 19 9Reactionswith11Be.................. 19 1 Introduction 9.1 Elastic scattering of 11Be............ 19 This article is a review of progress made over the past a e-mail: [email protected] decade in reactions induced by light (A<20) radioactive Page 2 of 38 Eur. Phys. J. A (2016) 52: 123 beams at energies near to and below the Coulomb barrier (E/A ≤ 10 MeV). Studies of elastic scattering, breakup, transfer, and fusion reactions on targets with A>4 that were published between 2006 and 2015 are reported. Ex- perimental work is emphasized, together with a selection of some of the many relevant theoretical papers on these subjects. Early publications within this time frame have already been reviewed by Keeley et al. [1,2]. In addition, a review of reactions with weakly bound nuclei by Canto et al. [3], which discusses reactions induced by both stable and radioactive projectiles and includes extensive theoret- ical analyses of the data, has recently appeared. All three of these publications are valuable resources for assessing the progress and future directions in this area in light of the fact that more exotic beams at higher intensity are becoming available. Fig. 1. Elastic scattering of 6He on 9Be at 16.8 MeV. Figure reprinted from ref. [4] with kind permission of The European 2 Reactions with 6He Physical Journal (EPJ). Reactions induced by 6He have continued to be a fruitful area of research in the last decade, both because of the superior agreement with the data, illustrating the effect of neutron-halo nature of this nuclide and the relative ease the projectile breakup channel on the elastic scattering. A of producing intense beams of it at energies near to and total reaction cross section of 1436 mb was deduced. In ad- dition, quasifree scattering of 6He on an α-particle cluster below the Coulomb barrier. Over 150 articles reporting on 9 fusion, elastic scattering, and breakup reactions, approx- in Be was studied, together with two-neutron stripping to states in 11Be. imately 1/3 of them experimental, have appeared during 6 9 this period. The experimental papers, and some of the Additional data for elastic scattering of He on Be more important theoretical work, are reviewed below. were obtained at Elab =16.2 and 21.3 MeV by Pires et al. [7]. The effect of target and projectile excitation was studied via coupled-channels calculations including cou- 2.1 Elastic scattering of 6He pling to the first three members of the ground-state ro- tational band in 9Be and the 2+ state in 6He. The ro- 6 tational couplings were found to have only a minor ef- Elastic scattering of He and other light radioactive nu- + clei on various targets was last reviewed by Keeley et al. fect, while the coupling to the 2 resonance improved the in 2009 [1]. Work that appeared after this publication is agreement with experiment. Three-body and four-body emphasized below. CDCC calculations were also performed, and it was found that a dominant role is played by nuclear couplings to the 2+ resonance. Surprisingly, the trivial local potentials ex- 2.1.1 6He + 6,7Li tracted from these calculations displayed the long-range absorption effects found for heavier targets, even though All available elastic-scattering data on these systems are the interaction is mainly nuclear rather than Coulomb in reviewed in ref. [1]. this system. An additional analysis of this same data set was presented in ref. [8]. Average total reaction cross sec- tions of 1525(104) mb and 1527(106) mb at 16.2 MeV and 2.1.2 6He + 9Be 21.3 MeV, respectively, were deduced. This implies an en- hancement of ≈ 25% in comparison with stable systems. Elastic scattering of 6He on 9Be has been measured at an incident energy of 16.8 MeV by Majer et al. [4], as part of a project to study 7He produced via the 9Be(6He, 8Be)7He 2.1.3 6He + 12Cand6He + 27Al reaction. The measured angular distribution, shown in fig. 1, is compared with data for 6Li + 9Be scattering All available elastic-scattering data on these systems are at 16.6 MeV [5]. Optical-model (OM) and continuum- reviewed in ref. [1]. discretized coupled-channels (CDCC) calculations are also shown. The optical-model calculations were performed by varying the real and imaginary well depths of the 6Li+9Be 2.1.4 6He + 51V potential of Cook and Kemper [6]. They begin to differ ◦ 6 9 ◦ 6 from the data at angles θc.m. > 100 for Li+ Be and 70 Angular distributions for He quasielastic scattering on for 6He + 9Be. A CDCC calculation coupling to the 6He 51V at laboratory energies of 15.4 and 23.0 MeV are re- continuum above the α + 2n breakup threshold provides ported in ref. [9]. The data at 23.0 MeV were compared Eur. Phys. J. A (2016) 52: 123 Page 3 of 38 Fig. 3. Elastic scattering of 6He on 206Pb. Figure reprinted with permission from ref. [13]. c 2013, The American Physical Society. 2.1.7 6He + 120Sn Fig. 2. Elastic scattering of 6He on 58Ni from ref. [10]. The elastic scattering of 6He on 120Sn has been studied at 4 with He scattering data at 23.2 MeV taken at the same Elab =17.40, 18.05, 19.80, and 20.5 MeV [11]. The angular time. Optical-model calculations showed that 6He is far distributions were analyzed using the optical model, and more absorbed than 4He. The 6He + 51V total reaction also a four-body CDCC calculation. The latter followed cross sections were found to be 1836 mb and 2219 mb at the methodology laid out in ref. [12] and included coupling 15.4 and 23.0 MeV, respectively. to the breakup channel. The total reaction cross sections extracted from these analyses were compared with those from elastic scattering of stable projectiles, both strongly- 2.1.5 6He + 58Ni and weakly-bound, on several targets. It was observed that the reduced total reaction cross sections for 6He were Elastic-scattering angular distributions for 6He on 58Ni at greater than those of weakly-bound stable nuclei, which Elab =12.2, 16.5, and 21.7 MeV were presented in ref. [10]. in turn were greater than those for strongly-bound pro- The data were analyzed via three-body and four-body jectiles.
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