Fusion, transfer and breakup of light weakly bound nuclei at near barrier energies.

1. Fusion, transfer and breakup of light weakly bound nuclei at near barrier energies. Paulo R. S. Gomes Univ. Fed. Fluminense (UFF), Niteroi, Brazil Eurisol Week Lisbon, Portugal – October 2012

2. Reactions with weakly bound nuclei

3. However, nature is more complicated than that simple picture: Breakup following transfer n p RESULTS after before measured measured known calculated by p conservation Courtesy of Luong

4. Breakup mechanism: Q-values n d RESULTS

5. Usual questions -Does the BU channel enhance or suppress the fusion cross section? Is the effect on σCF orσTF= CF + ICF? -What are the effects on different energy regimes and on different target mass regions? • Different BU threshold energies should affect NCBU significantly.Is that true for CFor CF + ICF? And for TR ? • May prompt and delayed BU affect fusion?

6. Usual questions • HowlargeistheNCBU compared with CF or CF + ICF ? How does it depend on the energy region and target mass? • Is transfer important for every weakly bound projectiles? • Does direct BU and BU following transfer produce repulsive polarization potentials? • Is there BTA for the elastic scattering of any weakly bound projectile?

7. Experimental aspects to be considered • What is it measured? σCF orσTF= CF + ICF? • Can ICF be separated from transfer channels leading to the same compound nucleus? So, instead of TF, one measures TF + transfer? • How to distinguish NCBU from transfer and ICF by measuring single fragments?

8. Importance of transfer for fusion of 6He. Is it also important for other weakly bound nuclei? If yes, how to separate it from total fusion? Raabe – Nature 431, 823(2004) X Trotta – PRL 84, 2342(2000) - same authors

9. Frequently used procedures to answer “Enhancement or suppression in relation to what? • Comparison of data with theoretical predictions. b) Comparison of data for weakly and tightly bound systems.

10. Effects to be considered • Static effects: longer tail of the optical potential arising from the weakly bound nucleons. • Dynamical effects: strong coupling between the elastic channel and the continuum states representing the break-up channel.

12. Example: 6He + 209Bi Single channel - no halo Single channel – with halo CC with bound channels (schematic calculation) • Shortcomings of the procedure: • Choice of interaction plays fundamental role • Does not allow comparisons of different systems • Difficult to include continuum – no separate CF and ICF

13. Example of Model Dependent Conclusions Kolata et al., PRL 81, 4580 (1998) Gomes et al., PLB 695, 320 (2011)

14. Raabe et al: Nature 431 (2004) 823 Important:Bare Potential deduced from double-folding procedure Gomes et al, PLB 695, 320 (2011) If one uses folding potentials, the halo density is taken into account. So, one does not observe halo effects!!!

15. Conclusions about static effects of halo nuclei. • Fusion enhancement when compared with what it should be without halo properties. • We believe that there is no more discussion left about that.

16. Differences due to static effects:

17. Fusion functions F(x) (our reduction method) Inspired in Wong’s approximation F0(x) = Universal Fusion Function (UFF) system independent !

18. Direct use of the reduction method Refining the method Eliminate the failure of the Wong model for light systems at sub-barrier energies

19. Applications with weakly bound systems Canto, Gomes, Lubian, Chamon, Crema, J.Phys. G36 (2009) 015109; NPA 821(2009)51 Gomes, , Lubian, Canto, PRC 79 (2009) 027606 Gomes, Canto, Lubian, Hussein, PLB 695 (2011), 320

20. Use of UFF for investigating the role of BU dynamical effects on the total fusion of heavyweakly bound systems No effect above the barrier- large enhancement below the barrier

21. Use of UFF for investigating the role of BU dynamical effects on the total fusion of very lightweakly bound systems No effect above the barrier- almost no data below the barrier

22. Use of UFF for investigating the role of BU dynamical effects on thetotal fusion of lightweakly bound systems No effect above the barrier- no data below the barrier

23. Is TF really total fusion or total fusion + transfer? Fang – submitted to publication

24. Use of UFF for investigating the role of BU dynamical effects on the complete fusionof stable weakly bound heavysystems We did not include any resonance of the projectiles in CCC. Suppression above the barrier- enhancement below the barrier

25. Fusion of neutron halo 6,8He, 11Be weakly bound systems

26. 6He + 206PB (Dubna data) ????

27. New 6He + 206Pb data (Wolski – EPJA 47, 111 (2011))

28. Application : transfer coupling effects on medium-heavy systems Shorto – PRC 81, 044601 (2010) Only inelastic channels were considered Zhang – PRC 82, 054609 (2010)

29. What about proton-halo systems?So far, there is only one system measured • Fusion of proton-halo 8B + 58Ni (Aguilera PRL 107, 092701 (2011))

30. Fusion of proton-halo 8B + 58Ni (Aguilera PRL 107, 092701 (2011)) New dynamic effect for proton-halo fusion? New measurements are required Rangel – submitted to publication

31. Two independent calculations without any fit parameter (Rangel et al., submitted to publication) CCC with SPP CDCC calculations

32. Conclusion from the systematic (several systems) : CF enhancement at sub-barrier energies and suppression above the barrier, when compared with what it should be without any dynamical effect due to breakup and transfer channels. Question: Why?

33. What has to be done? - Need of additional data at the sub-barrier energy regime. We still do not fully understand this important energy regime, very important for nucleosynthesis and production of SHE. • Need of more data with radioactive beams. We need better data, with smaller error bars. • More fusion cross section measurements for proton-halo nuclei. - More separated CF and ICF data, specially for light and medium mass systems. Can we separate transfer? • - Sub-barrier total fusion for light targets. Is there enhancement? • - CF and ICF for light systems, below and above the barrier. Is ICF negligible? • - CF and ICF for medium mass targets. How does the suppression vary with mass?

34. Final Message Although we have learned a lot in the last years, we still have many things to learn. We need more good data and more calculations and theoretical developments.

35. Collaborators J. Lubian, D. R. Otomar, R. Linares (UFF), L. F. Canto (UFRJ), M.S. Hussein (USP), M. Dasgupta, D. J. Hinde, D.H. Luong (ANU)