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

Reactions with weakly bound nuclei

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

Breakup mechanism: Q-values RESULTS n d

Usual questions -Does the BU channel enhance or suppress the fusion cross section? Is the effect on σ CF or σ TF= 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  CF or  CF + ICF ? And for  TR ? -May prompt and delayed BU affect fusion?

Usual questions How large is the  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?

Experimental aspects to be considered What is it measured? σ CF or σ TF= 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?

Importance of transfer for fusion of 6 He. 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

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

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.

Example: 6 He Bi 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

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

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

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.

Differences due to static effects :

Fusion functions F(x) (our reduction method) Inspired in Wong’s approximation F 0 (x) = Universal Fusion Function (UFF) system independent !

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

Applications with weakly bound systems 1. Canto, Gomes, Lubian, Chamon, Crema, J.Phys. G36 (2009) ; NPA 821(2009)51 2.Gomes,, Lubian, Canto, PRC 79 (2009) Gomes, Canto, Lubian, Hussein, PLB 695 (2011), 320

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

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

Use of UFF for investigating the role of BU dynamical effects on the total fusion of light weakly bound systems No effect above the barrier- no data below the barrier

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

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

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

6 He PB (Dubna data) ????

New 6 He Pb data (Wolski – EPJA 47, 111 (2011))

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

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

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

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

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?

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. - 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? - More separated CF and ICF data, specially for light and medium mass systems. Can we separate transfer?

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.

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)