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Recent results on reactions with radioactive beams at RIBRAS

Recent results on reactions with radioactive beams at RIBRAS. Alinka Lépine-Szily, and RIBRAS collaboration. ECT* workshop on Low-Energy Reaction Dynamics of Heavy-Ions and Exotic Nuclei May 26-30, 2014, Trento, Italy. Outline. Quick description of RIBRAS

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Recent results on reactions with radioactive beams at RIBRAS

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  1. Recent results on reactions with radioactive beams at RIBRAS Alinka Lépine-Szily, and RIBRAS collaboration ECT* workshop on Low-Energy Reaction Dynamics of Heavy-Ions and Exotic Nuclei May 26-30, 2014, Trento, Italy

  2. Outline • Quick description of RIBRAS • Elastic scattering measurements with 6He beam • Optical model and CDCC analysis • α-particle production • Total reaction cross sections • Elastic scattering and reactions on hydrogen target • R-matrix analysis and spectroscopic results

  3. Major Facility for Nuclear Physics research in Brazil Tandem Accelerator – Pelletron 8UD at the University of São Paulo - Brazil primary beams: 6Li, 7Li , 10,11B, 9Be, 12C, 16,17,18O, ... 3.0 – 5.0 MeV/nucleon

  4. RIBRAS - Radioactive Ion Beams in Brazil First RIB facility in the Southern Hemisphere,installed in 2004 Low energy radioactive ion beam production with solenoid based system. University of São Paulo – Brazil • Max field 6.5 Tesla • versatile configuration • persistent mode • low LHe and LN2 consumption First scattering chamber 2nd scattering chamber

  5. Selection with the first solenoid angular acceptance 2 deg - 6 deg Maximum Bρ=1.8Tm 30msr primary beam, transfer reactions ΔE-E Si telescopes 1- primary target 2- collimator 3- Faraday cup 4- solenoid 5- lollipop blocker 6- collimator 7- scattering chamber, secondary target and detectors Beams of interest: 6He, only 16%, 8Li 65%

  6. Double solenoids (cross-over mode) Second solenoid helps cleaning the secondary beam: Degrader changes the Br of the particles with different Z (q) Solenoid -1 Solenoid - 2 Target Degrader in first scatt.chamber Detectors 3 new strip-detector telescopes ΔE E

  7. secondary ion reaction intensity / 1A of primary beam 6He 9Be(7Li,6He) 2 x 105 p/s 8Li 9Be(7Li,8Li) 106 p/s 7Be 3He(6Li,7Be) 6x105 p/s 7Be 6Li(7Li,7Be) 105 p/s 10Be 9Be(11B,10Be) 2 x 103 p/s 8B 3He(6Li,8B) 104 p/s 18F 12C(17O,18F) 104 p/s 17F 3He(16O,17F)d * Present radioactive beams at RIBRAS

  8. Scientific program at RIBRAS Elastic scattering: 6He +9Be,27Al,51V,58Ni,120Sn 7Be + 27Al, 51V (only first solenoid) 8Li + 9Be, 51V 8B + 27Al 8Li, 7Be, 9Be, 10Be on 12C 8Li + p, 6He + p Transfer reactions: 8Li(p,α)5He, 12C(8Li,9Li)11C Future: Break-up reactions Inelastic scattering Fusion – evaporation (two solenoids)

  9. Elastic scattering measurements with 6He beam Light, intermediate and heavy targets: 9Be, 27Al, 51V, 56Ni, 120Sn Static and dynamic effects with 6He halo nucleus Cluster model 6He = 4He +2n Weakly bound B.E.= 0.973 MeV Neutron Skin and halo: static effects Correlations and couplings between reaction mechanisms. binding energy (breakup) effect in elastic scattering: α production Analysis using Optical Model (São Paulo Potential-SPP), CDCC Total reaction cross sections.

  10. São Paulo Potential (SPP) – optical potential with non-local interaction L.C. Chamon, D. Pereira, M.S. Hussein, M.Alvarez, L.Gasques, B.V. Carlson, et al. PRC 66,014610 (2002)1.Pauli non-locality related with energy dependence Local-equivalent potential : v is the local relative speed 2. Double-foldingpotential : v(rpa): effective zero-range nucleon-nucleon interaction 3. Imaginarypart :W(r,E)= NI VLE (r,E) limitation:same geometry for W as for V

  11. 6He+27Al elastic scattering First results of RIBRAS Optical Model calculation São Paulo potential (NI~0.7 a=0.56(2)=normal nuclear diffuseness) 6He+51V elastic scattering Optical Model calculation São Paulo potential (N I~1.4(4) a=0.67(3) larger than normal nuclear absorption and diffuseness) more absorption

  12. 6He+9Be elastic scattering 6He is 3 body Borromean system 6Healpha+2n 3b-CDCC.... 6Healpha +n+n 4b-CDCC Coupled Channels calculation: includes low lying excited states of 9Be and 2+ state of 6He ( is more important) Optical Potential: real part: Sao Paulo potential Imaginary part: Wood-Saxon potential used for 6Li+9Be 3 and 4 body CDCC calculations for 6He (continuum discretized coupled-channel)

  13. 6He+120Sn elastic scattering

  14. 6He + 120Sn elastic scattering Details of the coupling to the break-up channel No-coupling to exited states, equiv to optical model calculation 4b-CDCC only nuclear coupling Good fit 4b-CDCC Coulomb + nuclear coupling

  15. 6He + 58Ni elastic scattering Comparison with CDCC calc. 3-body and 4-body CDCC calculations give different cross Sections at θcm > 40o. Excellent agreement with 4-body CDCC calculation

  16. Conclusions on angular distribution analyses: 6He + 120Sn. Comparison of CDCC calculations with and without coupling to continuum. Need for Nuclear + Coulomb coupling to continuum. 6He + 58Ni Need for 4-body CDCC to fit the data 6He + 51V Optical Model calculations with SPP. NI and aI has to be increased from 0.78 to 1.4(4) and 0.56 fm to 0.67(3) fm. Simulates long range absorption due to breakup coupling 6He + 27Al Optical Model calculations with SPP. NI and aI are the same as normal stable nuclei. No effect of breakup coupling. 6He + 9Be Comparison of CDCC calculations with and without coupling to continuum. Need for coupling to continuum to get good fit.

  17. Production of α-particles

  18. Large amount of alpha particles produced in 6He+120Sn and 6He+9Be reactions 6He+120Sn 6He+9Be 6He α-particles from projectile break-up + target break-up + contaminants

  19. Energy spectra and angular distributions of α-particles from 6He+120Sn collision 120Sn(6He,4He)122Sn 6He+120Sn 4He+120Sn+2n α-particles resulting from 2n-transfer reaction mostly

  20. Total reaction cross sections

  21. PHYSICAL REVIEW C PHYSICAL REVIEW C 71 71 , 017601 (2005) , 017601 (2005) Uncertainties in the comparison of fusion and reaction cross sections of different systems involving Uncertainties in the comparison of fusion and reaction cross sections of different systems involving 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. weakly bound nuclei weakly bound nuclei To compare fusion and total reaction cross sections of systems withdifferent projectiles and targets, including halo nuclei two recent reduction methods are available: P. R. S. Gomes, J. Lubian, I. Padron, and R. M. Anjos P. R. S. Gomes, J. Lubian, I. Padron, and R. M. Anjos ́ ́ ˆ ˆ ́ ́ ́ ́ Instituto de F Instituto de F ısica, Universidade Federal Fluminense, Av. Litor ısica, Universidade Federal Fluminense, Av. Litor anea, s anea, s n, Gragoat n, Gragoat a, Niter a, Niter oi, R.J., 24210-340, Brazil oi, R.J., 24210-340, Brazil / /

  22. First reduction method considered: reduced energy reduced reaction cross section Removes: Geometrical differences arising from sizes and charges Takes into account: anomalous large radii of weakly bound / halo nuclei Lowering of Coulomb barrier due to these Does not take into account: change in width of fusion barrier: important for fusion, ?? for total reaction cross section,

  23. Second reduction method considered: Canto et al. J. Phys. G36, 015109 (2009) Based on tunneling concept (Wong model) Fusion function RB,VB and hω = radius, height, curvature Coulomb barrier Universal Fusion Function (UFF) should fit F(χ) if tunneling concept holds Applied to total reaction cross section (Shorto et al. Phys.Lett.B678,77) However, peripheral reactions (breakup, transfer, inelastic) do not proceed through tunneling. Should it apply to total reaction cross section???

  24. Total reaction cross sections on A~120 targets First scaling: σred (6He +120Sn): enhancement of ~ 50% over σred(7Li+138Ba) Second scaling: Both scalings yield 3 trends: Lowest σred -> tightly bound described by UFF-SPP Higher σred -> weakly bound Highest σred -> halo projectile

  25. Total reaction cross sections on A~60 targets First scaling σred(6He + 58Ni,51V,64Zn,8B+60Ni): enhancement of ~ 40 - 50% over σred ( 6,7,8Li + A~60 targets)

  26. Total reaction cross sections on 27Al target First scaling No enhancement for halo nuclei over weakly bound but over tightly bound Second scaling No enhancement, UFF describes all systems

  27. Total reaction cross sections on 12C target First scaling Slight enhancement (15%) for halo nuclei over weakly bound Second scaling UFF describes weakly bound and halo systems. Enhancement over tightly bound (0.6 UFF)

  28. Comparison of total reaction cross section using first scaling: A~120 similar results Coupling to Coulomb breakup and σred highest for low energy halo nuclei, 6He and 8B A~60 1.0 < Ered < 1.5, 40-50% enhancement over stable, weakly bound projectiles Ered > 1.5 , enhancement reduced 27Al No enhancement of halo over stable weakly bound at any energy. Enhancement over tightly bound 16O proj. 12C No error bars on σred. Slight enhancement (15%) for halo nuclei over weakly bound at Ered >2.5 9Be Enhancement of 20-30% of 6He over weakly bound at Ered>5. Breakup of 9Be contributes. Nuclear breakup.

  29. Comparison of total reaction cross section using second scaling : A~120 similar results to first scaling F(χ)(6He) > F(χ)(6,7Li) > F(χ)(4He) UFF agrees with F(χ) of 4He +A system (only fusion) Peripheral reactions are important for 6He and weakly bound on heavy targets (Coulomb breakup, transfer) 27Al UFF agrees with F(χ) of stable, tightly bound (16O), weakly bound and halo projectiles (only fusion ?) Very little peripheral reactions even for halo and weakly bound on 27Al target ? 12CUFF agrees with F(χ) of halo and stable weakly bound projectiles ???? 0.6 UFF agrees with F(χ) of tightly bound 4He and 12C projectiles ????

  30. Measurements with purified radioactive beams: Elastic scattering and transfer reactions on hydrogen target

  31. Interest of 8Li(p,)5He, 8Li(p,p)8Li and 8Li(p,d) reactions: Nuclear Physics: • Provide spectroscopic information on 9Be states near the p+8Li threshold (16.88 MeV) Astrophysics: • The reaction 8Li(p,)5He destroys the 8Li, preventing the access to higher mass nuclei. • Important to measure and compare its strength with the branch 8Li(,n)11B • Previously we have measured the excitation function for 8Li(p,)5He reaction between Ecm=0.2 -2.12 MeV,

  32. 2.467 MeV α+5He

  33. Inelastic scattering 9Be(p,p´) with 180 MeV p beam.Dixit et al, Phys.Rev. C43, 1758(1991) Resonances with strong α structure Our results of p(8Li,α) reaction. Mendes et al, Phys. Rev. C86, 064321 (2012)

  34. Results of our previous 8Li(p,)5He measurement: R-matrix fits: • Spins • Energies • Proton and alpha widths Astrophysical reaction rates

  35. The measurement of the 8Li(p,p)8Li elastic scattering can help to constrain the resonance parameters We measured simultaneously the 8Li(p,p)8Li, 8Li(p,)5He and 8Li(p,d)7Li reactions between Ecm = 0.8 – 2.0 MeV.

  36. Experimental method for the measurement: Inverse kinematics: 8Li beam hitting thick CH2target Primary beam 7Li, accelerated by 8UD Pelletron tandem of São Paulo Radioactive 8Li beam9Be(7Li,8Li)8Be, selected by the both solenoids of RIBRAS. Degrader between the solenoids. Production target: 16 micron 9Be foil Radioactive beam intensity: 3x105 pps (50% transmission from 1st to 2nd solenoid) Detection: deltaE(20 microns)-E(1000 microns), 300 mm2 silicon telescopes Secondary Target – C1H2 – 7.7 mg/cm2

  37. Experimental method: thick secondary target CH2 of 7.7 mg/cm2 Resonances populated in the target. Energy spectrum of 4He, p, d yields excitation function of resonance reaction 4He, p Si-telescope 8Li beam E2 E1 ε = stopping power

  38. Energy spectra measured on thick CH2 target at Elab=18.5 MeV Protons hard to measure, due to low energy (Q=0) and electronic noise

  39. ΔE=50μm 8Li(p,α)5He ΔE=20μm

  40. Resonances in 9Be at Ecm 0,40 0,60 1,10 1,69 1,76 MeV Contaminant light particles subtracted (Au target) C(8Li,p,d,α) reactions measured, subtracted 8Li(p,p)8Li 8Li(p,α)5He 8Li(p,d)7Li Ecm (MeV)

  41. 7Li(d,p)8Li Ecm(MeV) Resonances at 1.66 and 1.76 MeV decay to 7Li* (0.477MeV), not to 7Ligs, not populated in 7Ligs(d,p)8Li. Peak shifted to lower energy.

  42. R-matrix analysis of three excitation functions with AZURE 1.66 and 1.76MeV

  43. R-matrix analysis results (Masters Thesis of Erich Leistenschneider 04/2014) Black numbers Tilley et al Nuc. Phys. A745, 155 (2004) Blue numbers our analysis

  44. Comparison with previous work

  45. With parameters of the previous work With parameters of the previous work + width for (p,d) channel

  46. Conclusions • Elastic scattering measurements with 6He beam on light (9Be, 27Al), medium (51V,58Ni) and heavy (120Sn) targets. • Optical model and CDCC analysis: for medium and heavy targets, long range absorption, coupling to Coulomb+ nuclear breakup. • Light targets: 27Al, normal OM. 9Be, CDCC fits the data with coupling to continuum. • Total reaction cross sections: strong enhancement with halo projectiles on medium and heavy targets. Coulomb coupling . No enhancement on 27Al. Slight enhancement on 9Be and 12C targets. Nuclear coupling • The simultaneous measurement of resonant elastic scattering 8Li(p,p)8Li, 8Li(p,α)5He and 8Li(p,d)7Li reactions, allows to determine the resonance parameters of 9Be.

  47. Thank you Alinka Lépine-Szily (USP) and RIBRAS collaboration, as: USP: Rubens Lichtenthaler, Kelly C.C. Pires, Erich Leistenschneider, Valdir Guimarães, Valdir Scarduelli U. Sevilla M. Rodriguez-Gallardo and A. M. Moro ULB (Belgium) Pierre Descouvemont UFF (Niteroi) Djalma R. Mendes Jr, Pedro Neto de Faria, Paulo R.S. Gomes UNIFEI Viviane Morcelle UFBa Adriana Barioni GSI Juan Carlos Zamora TANDAR (Argentina) Andres Arazi USC Elisangela A. Benjamim

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