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. 1.Quick description of RIBRAS 2.Elastic scattering measurements with 6He beam 3.Optical model and CDCC analysis 4.α-particle production 5.Total reaction cross sections 6.Elastic scattering and reactions on hydrogen target 7.R-matrix analysis and spectroscopic results Outline

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

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

5. Production target Solid targets: 9 Be, LiF, 12 C etc or gas targets PRIMARY BEAM 30 cm solenoid bore collimator solenoid Angular acceptance

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

7. First solenoid: Bρ selection, cocktail of secondary beams with same Bρ Particles detected in the first scattering chamber Beam of interest: 6 He, only 16%Beam of interest: 8 Li, ~66%

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

9. Using both solenoids with degrader between them Particles detected in the second scattering chamber

10. secondary ion reaction intensity / 1  A of primary beam 6 He 9 Be( 7 Li, 6 He) 2 x 10 5 p/s 8 Li 9 Be( 7 Li, 8 Li) 10 6 p/s 7 Be 3 He( 6 Li, 7 Be) 6x10 5 p/s 7 Be 6 Li( 7 Li, 7 Be) 10 5 p/s 10 Be 9 Be( 11 B, 10 Be) 2 x 10 3 p/s 8 B 3 He( 6 Li, 8 B) 10 4 p/s 18 F 12 C( 17 O, 18 F) 10 4 p/s 17 F 3 He( 16 O, 17 F)d * Present radioactive beams at RIBRAS

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

12. Elastic scattering measurements with 6 He beam Light, intermediate and heavy targets: 9 Be, 27 Al, 51 V, 56 Ni, 120 Sn Static and dynamic effects with 6 He 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.

13. 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 : 2. Double-folding potential : v(r pa ): effective zero-range nucleon-nucleon interaction 3. Imaginary part : W(r,E)= N I V LE (r,E) limitation:same geometry for W as for V v is the local relative speed

14. 6 He+ 27 Al elastic scattering Optical Model calculation São Paulo potential (N I ~0.7 a=0.56(2)=normal nuclear diffuseness) First results of RIBRAS 6 He+ 51 V elastic scattering more absorption Optical Model calculation São Paulo potential (N I ~1.4(4) a=0.67(3) larger than normal nuclear absorption and diffuseness)

15. 6 He+ 9 Be elastic scattering Coupled Channels calculation: includes low lying excited states of 9 Be and 2 + state of 6 He ( is more important) Optical Potential: real part: Sao Paulo potential Imaginary part: Wood-Saxon potential used for 6 Li+ 9 Be 3 and 4 body CDCC calculations for 6 He (continuum discretized coupled-channel) 6 He is 3 body Borromean system 6 He  alpha+2n 3b-CDCC.... 6 He  alpha +n+n 4b-CDCC

16. 6 He+ 120 Sn elastic scattering

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

18. 6 He + 58 Ni elastic scattering Comparison with CDCC calc. 3-body and 4-body CDCC calculations give different cross Sections at θ cm > 40 o. Excellent agreement with 4-body CDCC calculation

19. Polarization potentials for the 6 He+ 58 Ni system

20. Conclusions on angular distribution analyses: 6 He + 120 Sn. Comparison of CDCC calculations with and without coupling to continuum. Need for Nuclear + Coulomb coupling to continuum. 6 He + 58 Ni Need for 4-body CDCC to fit the data 6 He + 51 V Optical Model calculations with SPP. N I and a I 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 6 He + 27 Al Optical Model calculations with SPP. N I and a I are the same as normal stable nuclei. No effect of breakup coupling. 6 He + 9 Be Comparison of CDCC calculations with and without coupling to continuum. Need for coupling to continuum to get good fit.

21. Production of α-particles

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

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

24. Total reaction cross sections

25. Total reaction cross section can be deduced from elastic scattering analysis. To compare fusion and total reaction cross sections of systems with different projectiles and targets, including halo nuclei two recent reduction methods are available: This information is useful to investigate the role of breakup (or other reaction mechanisms) for weakly-bound / exotic nuclei. PHYSICAL REVIEW C71, 017601 (2005) Uncertainties in the comparison of fusion and reaction cross sections of different systems involving weakly bound nuclei P. R. S. Gomes, J. Lubian, I. Padron, and R. M. Anjos Instituto de Fısica, Universidade Federal Fluminense, Av. Litor ˆ anea, s / n, Gragoata, Niter oi, R.J., 24210-340, Brazil PHYSICAL REVIEW C71, 017601 (2005) Uncertainties in the comparison of fusion and reaction cross sections of different systems involving weakly bound nuclei P. R. S. Gomes, J. Lubian, I. Padron, and R. M. Anjos Instituto de Fısica, Universidade Federal Fluminense, Av. Litor ˆ anea, s / n, Gragoata, Niter oi, R.J., 24210-340, Brazil

26. 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, First reduction method considered:

27. Second reduction method considered: Canto et al. J. Phys. G36, 015109 (2009) Fusion function Based on tunneling concept (Wong model) R B,V B and hω = radius, height, curvature Coulomb barrier Universal Fusion Function (UFF) should fit F(χ) 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)

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

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

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

31. Total reaction cross sections on 12 C 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)

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

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

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

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

36. α+ 5 He 2.467 MeV

37. Inelastic scattering 9 Be(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)

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

39. 39 The measurement of the 8 Li(p,p) 8 Li elastic scattering can help to constrain the resonance parameters We measured simultaneously the 8 Li(p,p) 8 Li, 8 Li(p,  ) 5 He and 8 Li(p,d) 7 Li reactions between E cm = 0.8 – 2.0 MeV.

40. Experimental method for the measurement: Inverse kinematics: 8 Li beam hitting thick CH 2 target Primary beam 7 Li, accelerated by 8UD Pelletron tandem of São Paulo Radioactive 8 Li beam 9 Be( 7 Li, 8 Li) 8 Be, selected by the both solenoids of RIBRAS. Degrader between the solenoids. Production target: 16 micron 9 Be foil Radioactive beam intensity: 3x10 5 pps (50% transmission from 1 st to 2 nd solenoid) Detection: deltaE(20 microns)-E(1000 microns), 300 mm 2 silicon telescopes Secondary Target – C 1 H 2 – 7.7 mg/cm 2

41. Experimental method : thick secondary target CH 2 of 7.7 mg/cm 2 Resonances populated in the target. Energy spectrum of 4 He, p, d yields excitation function of resonance reaction 8 Li beam E1E1 E2E2 Si-telescope 4 He, p ε = stopping power

42. Energy spectra measured on thick CH 2 target at Elab=18.5 MeV Protons hard to measure, due to low energy (Q=0) and electronic noise

43. ΔE=50μm ΔE=20μm 8 Li(p,α) 5 He

44. 0,40 0,60 1,10 1,69 1,76 MeV Resonances in 9 Be at E cm 8 Li(p,p) 8 Li 8 Li(p,α) 5 He 8 Li(p,d) 7 Li E cm (MeV) Contaminant light particles subtracted (Au target) C( 8 Li,p,d,α) reactions measured, subtracted

45. E cm (MeV) 7 Li(d,p) 8 Li Resonances at 1.66 and 1.76 MeV decay to 7 Li* (0.477MeV), not to 7 Li gs, not populated in 7 Li gs (d,p) 8 Li. Peak shifted to lower energy.

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

47. 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

48. Comparison with previous work

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

50. Conclusions Elastic scattering measurements with 6 He beam on light ( 9 Be, 27 Al), medium ( 51 V, 58 Ni) and heavy ( 120 Sn) targets. Optical model and CDCC analysis: for medium and heavy targets, long range absorption, coupling to Coulomb+ nuclear breakup. Light targets: 27 Al, normal OM. 9 Be, 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 27 Al. Slight enhancement on 9 Be and 12 C targets. Nuclear coupling The simultaneous measurement of resonant elastic scattering 8 Li(p,p) 8 Li, 8 Li(p,α) 5 He and 8 Li(p,d) 7 Li reactions, allows to determine the resonance parameters of 9 Be.

51. 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