Reaction studies with low-energy weakly-bound beams Alessia Di Pietro INFN-Laboratori Nazionali del Sud NN 2015Alessia Di Pietro,INFN-LNS

NN 2015Alessia Di Pietro,INFN-LNS Outline 1.Introduction 2.Elastic scattering of weakly-bound and halo nuclei. New results of: I. 6,7 Li+ 64 Zn II. 11 Be+ 197 Au III. 6 He+ 64 Zn 3.Direct reactions 4.Fusion 5.Summary and conclusions

NN 2015Alessia Di Pietro,INFN-LNS Exotic structures in light nuclei neutron halo neutron halo proton halo proton halo neutron drip line clusters 10 Be halo nucleus vs normal nucleus

NN 2015Alessia Di Pietro,INFN-LNS B(E1) distribution Halo nuclei: e.g. 11 Li, 11 Be, 6 He …. Weakly bound (easy to break-up) Easy to polarise (large B(E1) low energy strenght) Suffer lower Coulomb barrier Higher transfer probability T. Nakamura et al., Phys. Rev. Lett. 96, (2006). T. Aumann et al., Phys. Rev. C 59, 1252 (1999). N. Fukuda et al., Phys. Rev. C70, (2004).

NN 2015Alessia Di Pietro,INFN-LNS Effects of nuclear structure on collision: the elastic scattering process

NN 2015Alessia Di Pietro,INFN-LNS Elastic scattering of weakly bound 6,7 Li on 64 Zn INFN-LNS Above the barrier coupling to continuum effects more important in 6 Li than in 7 Li 6 Li+ 64 Zn 7 Li+ 64 Zn J.P.Fernandez-Garcia et al. submitted to PRC

M.Cubero et al., PRL109, (2012) Elastic scattering of halo nuclei A. Di Pietro et al. PRC 85, (2012) E lab =24.3 MeV 9,11 Li+ 208 Pb E lab =29.8 MeV Long range absorption effects of both, nuclear and Coulomb origin, accounts for suppression of elastic cross-section.

NN Be+ 197 Ge-array TIGRESS: - - detection of E  =0.32 MeV from 11 Be* beam  11 Be Calculations: XCDCC includes a non-spherical 10 Be core. Ι 11 Be(gs)> = a Ι 10 Be(gs)x 2s 1/2 > + b Ι 10 Be(2 + )x 1d 5/2 > + c Ι 10 Be(2 + )x 1d 3/2 > Charged particles: - 3 telescopes DSSSD (40µm) + PAD. - 1 telescope SSSD 16 (20 µm) + DSSSD (300 µm). Standard CDCC

NN 2015Alessia Di Pietro,INFN-LNS New data 6 He+ 64 E lab ≈ 15 and 18 MeV SSSD LAMP LEDA beam

NN 2015Alessia Di Pietro,INFN-LNS Comparison between 4,6 He+ 64 Zn data at two beam energies 6 He+ 64 Zn E c.m. =12.4 MeV PRC 69,044613(2004) 6 He+ 64 Zn E c.m. =13.7 MeV 4 He+ 64 Zn The elastic angular distributions at two different energies are “almost” the same!

NN 2015Alessia Di Pietro,INFN-LNS 6 He+ 64 Zn elastic scattering It seems that the angular distributions at E lab =13.6 MeV and 15 MeV are the same is due to the different contribution of coupling with the trasfer channel ! PRC 69,044613(2004)

NN 2015Alessia Di Pietro,INFN-LNS Break-up and transfer processes A.M. Moro et al. PRC 89, (2014) P C T H Transfer Break-up 6 He+ 64 Zn 11 Be+ 64 Zn 10 Be angular distribution 11 Be+ 64 Zn P C T T+n V. Scuderi et al. PRC 84, (2011) 6 He+ 64 Zn  65 Zn PRC 84,064604(2011)

NN 2015Alessia Di Pietro,INFN-LNS Fusion

NN 2015Alessia Di Pietro,INFN-LNS ● There is an effect of the halo structure on fusion ● Static effects appears to be important but not the only ones ● CF appears to be dominant over ICF ● Few data below barrier No clear conclusions can be reached for p-halo nuclei see e.g. : 8 B+ 58 Ni - E.F. Aguilera et al.: PRL 107,092701,(2011) 8 B+ 28 Si - A.Pakou et al.: PRC87,014619,(2013) L.F. Canto et al.: NPA 821,51, (2009) ; P.R.S. Gomes et al.: PRC 79, , (2009) J.Rangel et al.: Eur. Phys. Jour A 49, 57, (2013); Halo nuclei Systematics for fusion with halo nuclei Main ingredient: reduce  Fus (E) to eliminate static effects Further transformation eliminates coupling to bound state effects Fusion of n-halo nuclei

NN 2015 L.F. Canto, Nucl. Phys. A 821 (2009) 51 Fusion of weakly bound nuclei with no halo structure Systematic on heavy M.Fisichella et al. to be published

NN 2015Alessia Di Pietro,INFN-LNS Break-up dynamics in 6,7 Li+ 144 Sm, 207 Pb and 209 Bi Break-up is triggered predominantly by nucleon transfer. From the relative energy of break- up fragments the time-scale of break-up was deduced and prompt break-up separated by asymptotic break-up.

Alessia Di Pietro,INFN-LNS A. Di Pietro et al. PHYS. REV. C 87, (2013) 6,7 Li+ 64 Zn heavy residue excitation function Ratio of H.R. cross-section NN 2015

Heavy Residue relative yields (  H.R. /  tot ) Experiment Complete Fusion calculations d-capture calculations  -capture calculations Is d or  capture from 6 Li important ? ● ICF E *  ( E cm - S  )x(m clu /m proj ) + Q (Clu+64Zn) ● Cluster transfer E *  Q gg – Q opt NN n or 1p transfer leading to 65 Zn and 65 Ga can also contribute Above barrier CF dominates Below the barrier different processes dominate A.Di Pietro et al. Phys. Rev. C 87, , (2013)

NN 2015Alessia Di Pietro,INFN-LNS Summary and conclusions Reaction studies with halo and weakly bound beams have shown many peculiarities due to the low binding and extended wave function :  Damping of elastic cross-section at large impact parameters due to the coupling to the continuum. Both Coulomb and nuclear coupling contribute to the effect.  Coupling to n-transfer important in 6 He elastic scattering.  Large total reaction cross-sections.  Large cross-section for transfer and breakup events. Different contribution for the different projectiles.  With weakly bound and halo nuclei the suppression of above barrier complete fusion could be due to break-up. Break-up triggered by nucleon transfer has been found to be more important than direct break-up. With lighter masses the observed enhancement below the barrier seem to be due to other processes contributing to the measured cross-section.

NN 2015Alessia Di Pietro,INFN-LNS RBI Zagreb