Valdir Guimares Universidade de So Paulo So Paulo Visiting Researcher at IPN-Orsay Universit Paris Sud - France Valdir Guimares Universidade de So Paulo So Paulo Visiting Researcher at IPN-Orsay Universit Paris Sud - France Dynamic and static effects in elastic scattering of light proton and neutron-rich nuclei Cluster configuration and low binding energies Borromean rings Halo nuleus Exotic nuclei 8 B = 7 Be + p (0.137 MeV) 6 He = 4 He + 2n (0.973 MeV) 8 He = 6 He + 2n (2.140 MeV) 11 Li = 9 Li + 2n (0.369 MeV) Weakly bound nuclei 7 Be = 4 He + 3 He (1.587 MeV) 9 Be = 8 Be + n (1.665 MeV) 6 Li = 4 He + d (1.474 MeV) 7 Li = 4 He + t (2.467 MeV) 8 Li = 7 Li + n (2.032 MeV) Tightly bound nuclei 16 O = 12 C + 4 He (7.192 MeV) 10 Be= 9 Be + n (6.812 MeV) 11 B = 7 Li + 4 He (8.664 MeV) 6 He 8 He 11 Li 15 N stable 15 C exotic, neutron-rich (drip-line) 3 Halo effect in exotic nuclei Borromean nuclei: 6 He, 8 He, 11 Li 2n 5 He= 4 He+n 10 Li= 9 Li+n 7 He= 6 He+n not bound Low two neutron binding energy 6 He = 4 He + 2n B.E.= MeV 11 Li = 9 Li + 2n B.E.= MeV 8 He = 6 He + 2n B.E.= MeV Borromean ring Symbol of Borromean family Castle near Maggiore lake Italy. Japonese families emblemes Elastic Scattering, why? Elastic scattering is a peripheral process and it probes the tail of the wave function. One can learn about surface properties, such as size of nuclei and surface diffuseness, halo structure (static effects). The longer tail of the nuclear density gives rise to a more diffuse potential and lower barrier. The peculiar structure of the exotic nuclei should affect the reaction properties and channel coupling (dynamic effects) becomes important. Breakup os a very important channel due to the low binding energy. Beams of radioactive nuclei has caused a revival of interest in elastic scattering. Elastic scattering is a peripheral process and it probes the tail of the wave function. One can learn about surface properties, such as size of nuclei and surface diffuseness, halo structure (static effects). The longer tail of the nuclear density gives rise to a more diffuse potential and lower barrier. The peculiar structure of the exotic nuclei should affect the reaction properties and channel coupling (dynamic effects) becomes important. Breakup os a very important channel due to the low binding energy. Beams of radioactive nuclei has caused a revival of interest in elastic scattering. The discovery of exotic nuclei renewed the interest in the investigation and modeling of nuclei reactions and structure. Talks of Moro, Diaz-Torres, Hagino, Lubian, Hussein and others The discovery of exotic nuclei renewed the interest in the investigation and modeling of nuclei reactions and structure. Talks of Moro, Diaz-Torres, Hagino, Lubian, Hussein and others 6 Universidade de So Paulo ( Brazil) University of Notre Dame (USA) 7 Be on 12 C 9 Be on 12 C 10 Be on 12 C 8 Li on 12 C 7 Be on 12 C 9 Be on 12 C 10 Be on 12 C 8 Li on 12 C 7 Be on 12 C 8 B on 12 C 7 Be on 12 C 8 B on 12 C Laboratorio Tandar (Argentina) 10 B on 58 Ni 11 B on 58 Ni 10 B on 58 Ni 11 B on 58 Ni 6 He on 58 Ni 7 Be on 58 Ni 8 B on 58 Ni 10 C on 58 Ni 7 Be on 58 Ni 8 B on 58 Ni 10 C on 58 Ni 6 He on 209 Bi Elastic Scattering measurements Systematic of elastic Scattering measurements 7 Threshold anomaly or breakup threshold anomaly Total reaction cross section (appropriate reduction) Interaction distance Threshold anomaly or breakup threshold anomaly Total reaction cross section (appropriate reduction) Interaction distance Get some physics out of elastic scattering data Angular distributions measured at different energies Energies close (below and above) to the Coulomb barrier Angular distributions measured at different energies Energies close (below and above) to the Coulomb barrier Data Analysis To get some physics Conventional Optical Model analysis using Wood-Saxon potential or double-folding potential (SPP) Cluster model and CDCC calculation with 3 or 4 body Coupled channel (inelastic+transfer) + CDCC (breakup) Potentials analysis - Short range + Long range Potentials Conventional Optical Model analysis using Wood-Saxon potential or double-folding potential (SPP) Cluster model and CDCC calculation with 3 or 4 body Coupled channel (inelastic+transfer) + CDCC (breakup) Potentials analysis - Short range + Long range Potentials Using of standard Wood-Saxon potential or double-folding potential (SPP) SPP (Sao Paulo Potential) L.C. Chamon, et al. PRC 66, (2002) Local-equivalent potential energy dependent : Double-folding potential : v(r pa ): effective zero-range nucleon-nucleon interaction Sao Paulo Potential Conventional Optical Model No Free Parameters From large systematics for stable projectiles Woods-Saxon Potential 6 free parameters 8 B, 7 Be, 6 Li+ 12 C elastic scattering Experiment with Twinsol at Notre Dame (2008) - USA 8 B + 12 C 7 Be + 12 C Woods-Saxon and double-folding (SSP) Optical Potentials 7 Be= 4 He+ 3 He (1.587 MeV) 8 B= 7 Be+p (0.138 MeV) 7 Be= 4 He+ 3 He (1.587 MeV) 8 B= 7 Be+p (0.138 MeV) 7 Be, 9 Be, 10 Be + 12 C elastic scattering Experiment with RIBRAS So Paulo - Brazil (2010) 10 Be + 12 C 9 Be + 12 C 7 Be + 12 C 7 Be and 10 Be Radioactive beams of about 10 4 pps Optical model analyses with double-folding So Paulo Potential Sao Paulo Potential 7 Be = 4 He + 3 He (1.587 MeV) 9 Be = 8 Be + n (1.665 MeV) 10 Be= 9 Be + n (6.812 MeV) Binding energies 8 B + 58 Ni elastic scattering Experiment with Twinsol at Notre Dame - USA Optical model folding SPP needs a N I =3.6 (normal is N I = 0.78) Optical Model WS Potential: too large imaginary potential depth Reaction cross section 8 B + 58 Ni 12 Nuclear Physics A 833, 2010, 156171 8 B + 58 Ni elastic scattering Parameter hides important physics information. Other channels are important Sao Paulo Potential From large systematics Low binding energy Strong cluster configuration (halo, borromean) strong influence of the breakup channel 13 n continuum Breakup effect Low binding energy of the projectile Breakup process involves unbound states and thus coupled channel including continuum is necessary CDCC (Continuum Discretized Coupled Channel) calculation and cluster model (with or without 3 and 4-body) Breakup effect Low binding energy of the projectile Breakup process involves unbound states and thus coupled channel including continuum is necessary CDCC (Continuum Discretized Coupled Channel) calculation and cluster model (with or without 3 and 4-body) Dynamic effect of breakup (CDCC) 3-Body interaction 4-Body interaction 14 8 B + 58 Ni elastic scattering - CDCC CDCC (Continuum Discretized Coupled Channel) CDCC+inelastic CDCC (Continuum Discretized Coupled Channel) CDCC+inelastic 15 Polarization potential effective potential that simulates the overall effect of the couplings Polarization potential is non-local Polarization potential L-dependent Averaging over L-dependency and taking as local: TLP ( Trivial Local Polarization) Polarization potential effective potential that simulates the overall effect of the couplings Polarization potential is non-local Polarization potential L-dependent Averaging over L-dependency and taking as local: TLP ( Trivial Local Polarization) Breakup effect Polarization long range potential Breakup effect Polarization long range potential Real bare potential (SPP with N R =1.00) + short range Imaginary + long range (polarization) real and imaginary potential Real bare potential (SPP with N R =1.00) + short range Imaginary + long range (polarization) real and imaginary potential Polarization Potential 16 Polarization Potential Short range Long range (surface peaked) 8 B + 58 Ni elastic scattering Polarization Potential 17 8 B + 58 Ni elastic scattering 18 6 He + 58 Ni elastic scattering CDCC + 3-body 4-body Experiment with RIBRAS - So Paulo Importance of CDCC and 3-body and 4-body description for 6 He. Polarization potential effective potential that simulates the overall effect of the couplings TLP ( Trivial Local Polarization) real part repulsive in the surface imaginary part attractive long range due to the breakup channel Polarization potential effective potential that simulates the overall effect of the couplings TLP ( Trivial Local Polarization) real part repulsive in the surface imaginary part attractive long range due to the breakup channel 19 Angular distributions show a smooth angular dependence and a total or partial absence of the Fresnel characteristic diffraction pattern. The cross section starts to deviate from the Rutherford formula at relatively small angles which, in a classical picture, would correspond to distant trajectories. The long-range absorption suggests the presence of reaction mechanisms that remove flux from the elastic channel at distances well beyond the strong absorption radius. Elastic scattering and interaction distance Elastic of exotic nuclei Interaction distance distance at which the nuclear interaction switches on, distance at which the elastic cross section ratio ( / ruth ) drops to 98% (S-matrix drops to 99%). Critical interaction distance distance of closest approach strong absortion / RUTH = 0.25 radius barrier (radius of top of barrier for L=0) critical interaction distance / RUTH = 0.98 DR becomes important DR is max P E falls off rapidly from unity Fusion becomes important D or DR = Direct Reaction E = Elastic D or DR = Direct Reaction E = Elastic Flux is almost completely absorbed Radii and distances in elastic scattering analysis strong absorption / RUTH = 0.25 barrier radius (radius of top of barrier for L=0) critical interaction distance / RUTH = 0.97 DR become important DR is max The nuclear force starts being effective at the tail of the potential, and for weakly bound nuclei a large diffuseness or a long range tail might be necessary. Radii and distances in elastic scattering analysis D or DR = Direct Reaction E = Elastic D or DR = Direct Reaction E = Elastic 23 6 Li+ 208 Pb Y. W. Wu PRC68(2003) 6,7 Li+ 208 Pb M. Dasgupta PRC70(2004) 8 Li+ 208 Pb E. Aguilera PRC 80 (2009) 6 Li+ 208 Pb Y. W. Wu PRC68(2003) 6,7 Li+ 208 Pb M. Dasgupta PRC70(2004) 8 Li+ 208 Pb E. Aguilera PRC 80 (2009) strong absorption / RUTH =0.25 barrier radius critical interaction distance Lithium isotopes 6 Li = 4 He + d (1.474 MeV) 7 Li = 4 He + t (2.467 MeV) 8 Li = 7 Li + n (2.032 MeV) 24 6 Li and 7 Be weakly bound nuclei Exotic nuclei 8 B = 7 Be + p (0.137 MeV) 6 He = 4 He + 2n (0.973 MeV) 8 He = 6 He + 2n (2.140 MeV) 11 Li = 9 Li + 2n (0.369 MeV) Weakly bound nuclei 7 Be = 4 He + 3 He (1.587 MeV) 9 Be = 8 Be + n (1.665 MeV) 6 Li = 4 He + d (1.474 MeV) 7 Li = 4 He + t (2.467 MeV) 8 Li = 7 Li + n (2.032 MeV) Tightly bound nuclei 16 O = 12 C + 4 He (7.192 MeV) 11 B = 7 Li + 4 He (8.664 MeV) 25 8 B and 11 B isotopes Exotic nuclei 8 B = 7 Be + p (0.137 MeV) 6 He = 4 He + 2n (0.973 MeV) 8 He = 6 He + 2n (2.140 MeV) 11 Li = 9 Li + 2n (0.369 MeV) Weakly bound nuclei 7 Be = 4 He + 3 He (1.587 MeV) 9 Be = 8 Be + n (1.665 MeV) 6 Li = 4 He + d (1.474 MeV) 7 Li = 4 He + t (2.467 MeV) 8 Li = 7 Li + n (2.032 MeV) Tightly bound nuclei 16 O = 12 C + 4 He (7.192 MeV) 11 B = 7 Li + 4 He (8.664 MeV) Experiment in Tandar - Argentina February 2014 Preliminary (unpublished) data 26 Polarization Potential Short range Long range 8 B Potential (Woods-Saxon) analysis 27 8 B Coupled Channel (CDCC) analysis 28 8 B = 7 Be + p (0.137 MeV) 2.37 fm 6 He = 4 He + 2n (0.973 MeV) 2.46 fm 7 Be = 4 He + 3 He (1.587 MeV) 2.04 fm Interaction distance 58 Ni target 6 He + 58 Ni elastic scattering CDCC + 3-body 4-body 29 The case of 11 Li on 208 Pb 11 Li 9 Li Forward angles pure Rutherford The 11 Li case 30 11 Li = 9 Li + 2n (0.369 MeV) 4.20 fm 6 Li = 4 He + d (1.474 MeV) 1.92 fm 8 Li = 7 Li + n (2.032 MeV) 2.04 fm 7 Li = 4 He + t (2.467 MeV) 1.80 fm 9 Li = 8 Li + n (4.064 MeV) 1.60 fm 11 Li - Interaction distance Interaction distance 208 Pb and 209 Bi targets 4.20 fm 1.60 fm 31 The 6 He case 32 Backscattering of 6 He on 209 Bi Measurements at University of Notre Dame 4.3 mg/cm 2 Solenoid -1 Solenoid - 2 Degrader or collimator 209 Bi target Detectors 6 He beam 6 He beam energies: 6 He beam intensity: 10 5 pps Production reaction 2 H( 7 Li, 6 He) 3 He Primary Target: Gas cell with 2 H at ~1.5 atm 12, 14 and 16 MeV Backscattering of 6 He on 209 Bi Experiment with Twinsol at Notre Dame - USA Max field 6 Tesla versatile configuration persistent mode low LHe and LN2 consumption Max field 6 Tesla versatile configuration persistent mode low LHe and LN2 consumption LAB = 30.0 LAB = 110 120 130 140 150 160 LAB = 160.6 LAB = 30.0 Left/Right: E (MeV) E TOTAL (MeV) 6 He LAB = 150.8 6 He 6 He (14 MeV) Typical E-E spectra angles: LAB = 110 120 130 140 150 160 3 Energies below barrier E LAB = 12.0, 14.0 and 16.0 MeV Interaction distance 36 Interaction distance 6 He on 209 Bi University of Notre Dame 6 He on 208 Pb Sanchez-Benitez - NPA803(2008)30 37 11 Li = 9 Li + 2n (0.369 MeV) 4.20 fm 6 He = 4 He + 2n (0.973 MeV) 2.25 fm 6 Li = 4 He + d (1.474 MeV) 1.92 fm 8 Li = 7 Li + n (2.032 MeV) 2.04 fm 7 Li = 4 He + t (2.467 MeV) 1.80 fm 9 Li = 8 Li + n (4.064 MeV) 1.60 fm Interaction distance 2.25 fm 6 He on 209 Bi University of Notre Dame 6 He on 208 Pb Sanchez-Benitez - NPA803(2008)30 38 Elastic scattering of the brunian nucleus 10 C+ 58 Ni Experiment with Twinsol at Notre Dame - USA OCT-2014 cluster configuration 10 C = 6 Be+ 4 He (5.101 MeV) = 9 B+p (4.005 MeV) = 8 Be+2p (3.821 MeV) 10 C brunian nucleus = super borromean nucleus (4 interactions) angular distribution being analyzed 10 C = 4 He+ 4 He+p+p Experiment 10 C MeV Beam energy: 32 MeV Beam intensity 105 pps Production reaction 3 He( 10 B, 10 C) 10 C 12 N 10 B 9 Be 6 Li 4 He Summary Despite the fact that large laboratories are pushing to produce all kinds of exotic and very energetic species of nuclei, some efforts have also been devoted by small laboratories. Low energy beams can be use to investigate reactions such as elastic, transfer and breakup. With the improvement of radioactive ion beam production it is now possible to obtain reliable measurement of reactions induced by unstable nuclei Elastic scattering measurement induced by low energy radioative ion beam is a very useful tool to investigate dynamic and static effects in exotic nuclei. Despite the fact that large laboratories are pushing to produce all kinds of exotic and very energetic species of nuclei, some efforts have also been devoted by small laboratories. Low energy beams can be use to investigate reactions such as elastic, transfer and breakup. With the improvement of radioactive ion beam production it is now possible to obtain reliable measurement of reactions induced by unstable nuclei Elastic scattering measurement induced by low energy radioative ion beam is a very useful tool to investigate dynamic and static effects in exotic nuclei. A.Arazi (Tandar) International collaboration V. Guimares (USP) D. S. Monteiro (USP) V. Scarduelli (USP) V. Morcelle (UFRRJ) E. S. Rossi Jr. (UNIFIEO) J. Lubian (UFF) A.Lepine (USP) R. Lichtenthaler (USP) P. Neto de Faria (UFF) D. Mendes (UFF) L. Gasques (USP) V. Guimares (USP) D. S. Monteiro (USP) V. Scarduelli (USP) V. Morcelle (UFRRJ) E. S. Rossi Jr. (UNIFIEO) J. Lubian (UFF) A.Lepine (USP) R. Lichtenthaler (USP) P. Neto de Faria (UFF) D. Mendes (UFF) L. Gasques (USP) E. F. Aguilera, E. Martinez-Quiroz, D. Lizcano, Paulina Amador-Valenzuela E. F. Aguilera, E. Martinez-Quiroz, D. Lizcano, Paulina Amador-Valenzuela J. J. Kolata (UND) Amy Roberts (UND) Alan Howard (UND) F. D. Becchetti (UMICH) R. Torres-Isea, (UMICH) Michael Febbraro (UMICH) J. J. Kolata (UND) Amy Roberts (UND) Alan Howard (UND) F. D. Becchetti (UMICH) R. Torres-Isea, (UMICH) Michael Febbraro (UMICH) Thank you solenoid collimator Block lollipop`` Different particles have different B B Solenoid beam selection Production target Solid 9 Be or 2 H, 3 He Gas 7 Li+ 2 H = 8 Li 7 Li 6 He 4 He 3 He t,d,p Elastic scattering Charge Exchange Transfer Fusion evaporation Elastic scattering Charge Exchange Transfer Fusion evaporation detector 43 44 Reduction procedure Geometrical effects such as masses and charges of the collision partners are removed. Possible anomalous values of the reduced radius r 0 are not washed out. r 0 could be related to physical processes or specific static feature of the projectile Geometrical effects such as masses and charges of the collision partners are removed. Possible anomalous values of the reduced radius r 0 are not washed out. r 0 could be related to physical processes or specific static feature of the projectile To compare systems with different Coulomb barriers and different geometry, It is necessary to suppress differences arising from the size and charges. Removing geometric but leaving other static effects Total reaction cross section Total reaction cross section can be deduced from elastic scattering analysis. This information is useful to investigate the role of breakup (or other reaction mechanisms) for weakly-bound, exotic nuclei. Total reaction cross section can be deduced from elastic scattering analysis. This information is useful to investigate the role of breakup (or other reaction mechanisms) for weakly-bound, exotic nuclei. How to compare systems with different Coulomb barriers and different geometry, 8 B+ 58 Ni 6 Li, 7 Li, 7 Be, 9 Be 16 O 6 He+ 27 Al 6 He+ 209 Bi 6 He+ 64 Zn Reduced total reaction cross section Reaction enhancement for exotic nuclei (transfer and/or breakup) Exotic nuclei 8 B = 7 Be + p (0.137 MeV) 6 He = 4 He + 2n (0.973 MeV) 8 He = 6 He + 2n (2.140 MeV) 11 Li = 9 Li + 2n (0.369 MeV) Wealy bound nuclei 7 Be = 4 He + 3 He (1.587 MeV) 9 Be = 8 Be + n (1.665 MeV) 6 Li = 4 He + d (1.474 MeV) 7 Li = 4 He + t (2.467 MeV) 8 Li = 7 Li + n (2.032 MeV) Tightly bound nuclei 16 O = 12 C + 4 He (7.192 MeV) 11 B = 7 Li + 4 He (8.664 MeV) Reduced total reaction cross section 4 He and 6 He 48 Fusion function Based on tunneling concept (Wong model) R B,V B = radius, height h = curvature Coulomb barrier Universal Fusion Function (UFF) should fit F() if tunneling concept holds However, peripheral reactions (breakup, transfer, inelastic) do not proceed through tunneling. Should it apply to total reaction cross section??? Applied to total reaction cross section (Shorto et al. Phys.Lett.B678,77) Second reduction method considered: Removing static and geometric leaving dynamic effects UFF= 49 Reduced total reaction cross sections on 12 C and 9 Be target Solid line UFF describes weakly bound and halo systems. Enhancement over tightly bound (0.6 UFF) 50 Solid line UFF Scientific Program Fusion Direct Reactions: Elastic, inelastic Breakup Transfer Breakup reactions Elastic Scattering Resonant scattering Transfer reactions Fusion Evaporation Breakup reactions Elastic Scattering Resonant scattering Transfer reactions Fusion Evaporation Beams produced so far at Twinsol and RIBRAS intensities for 1 A of primary beam 9 Be( 7 Li, 6 He) 6 He p/s MeV ND and SP 9 Be( 7 Li, 8 Li ) 8 Li p/s MeV ND and SP 3 He( 6 Li, 7 Be) 7 Be p/s MeV ND and SP 3 He( 6 Li, 8 B ) 8 B p/s MeV ND and SP 9 Be( 11 B, 10 Be) 10 Be p/s 25 MeV ND and SP 3 He( 10 B, 10 C) 10 C p/s 30 MeV ND 3 He( 10 B, 11 C) 11 C p/s 30 MeV ND 3 He( 10 B, 12 N) 12 N p/s 35 MeV ND 9 Be( 11 B, 12 B) 12 B p/s 25 MeV SP 40 MeV ND 9 Be( 13 C, 14 C) 14 C p/s 30 MeV SP 9 Be( 7 Li, 6 He) 6 He p/s MeV ND and SP 9 Be( 7 Li, 8 Li ) 8 Li p/s MeV ND and SP 3 He( 6 Li, 7 Be) 7 Be p/s MeV ND and SP 3 He( 6 Li, 8 B ) 8 B p/s MeV ND and SP 9 Be( 11 B, 10 Be) 10 Be p/s 25 MeV ND and SP 3 He( 10 B, 10 C) 10 C p/s 30 MeV ND 3 He( 10 B, 11 C) 11 C p/s 30 MeV ND 3 He( 10 B, 12 N) 12 N p/s 35 MeV ND 9 Be( 11 B, 12 B) 12 B p/s 25 MeV SP 40 MeV ND 9 Be( 13 C, 14 C) 14 C p/s 30 MeV SP 8 Li and 6 He Beam contamination Elastic Scattering 3 mm X-Y spectrum for 8 Li beam 8 Li Au EE E RES particle Silicon Detectors LAB = 0 6 He p t EE E TOTAL = E + E RES 6 He p t E TOTAL 8 Li beam 6 He beam 54 Twinsol system at University of Notre Dame, USA RIBRAS Radioactive Ion Beams in Brazil Double solenoid system for radioactive ion beam production 55 Chamber: 70 cm dia. turntable. Double solenoid system for radioactive ion beam production Twinsol system at University of Notre Dame, USA Max field 6 Tesla versatil configuration persistent mode low LHe and LN2 consumption Max field 6 Tesla versatil configuration persistent mode low LHe and LN2 consumption 56 Elastic scattering of the brunian nucleus 10 C+ 58 Ni Experiment with Twinsol at Notre Dame - USA OCT-2014 cluster configuration 10 C = 6 Be+ 4 He (5.101 MeV) = 9 B+p (4.005 MeV) = 8 Be+2p (3.821 MeV) 10 C brunian nucleus = super borromean nucleus (4 interactions) angular distribution being analyzed 10 C = 4 He+ 4 He+p+p Experiment 10 C MeV Beam energy: 32 MeV Beam intensity 105 pps Production reaction 3 He( 10 B, 10 C) 10 C 12 N 10 B 9 Be 6 Li 4 He 57 Total reaction cross sections on 12 C target Slight enhancement (15%) for halo nuclei over weakly bound Reduced total reaction cross sections on 12 C target 58 6 He (skin) 8B8B Light exotic nuclei Drip-line nuclei Modelo de camadas e nmeros mgicos Reactions with exotic nuclei Dynamic effects due to its low binding energy Correlations and couplings between reaction mechanisms. Coupling to continuum (CDCC calculation), Breakup effect due to the low binding energy Dynamic effects due to its low binding energy Correlations and couplings between reaction mechanisms. Coupling to continuum (CDCC calculation), Breakup effect due to the low binding energy Static effect of skin and halo nuclei Associated with the longer tail of the nuclear density This tail gives rise to a more diffuse potential, with a lower barrier Their peculiar structure should affect the reaction properties Static effect of skin and halo nuclei Associated with the longer tail of the nuclear density This tail gives rise to a more diffuse potential, with a lower barrier Their peculiar structure should affect the reaction properties