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Matko Milin

Reactions induced by low energy 6 He beam. Matko Milin. Faculty of Science , University of Zagreb , Croatia. S.Blagus, D.Jelavić, Ð.Miljanić, N.Soić, M.Uroić, M.Zadro R uđer Bošković Institut e, Zagreb, Croatia. Introduction: light nuclei. neutron halo. proton halo. 10 He.

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Matko Milin

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  1. Reactions induced by low energy 6He beam Matko Milin Faculty of Science, University of Zagreb, Croatia S.Blagus, D.Jelavić, Ð.Miljanić, N.Soić, M.Uroić, M.Zadro Ruđer BoškovićInstitute, Zagreb, Croatia

  2. Introduction: light nuclei neutron halo proton halo 10He neutron skin neutron drip line

  3. Introduction: 6He structure • Borromean structure • two loosely bound neutrons orbiting an a-core • large interaction radius! • RRMS≈ 2.5 fm vs. RRMS(a)≈ 1.7 fm • components: di-neutron and cigar-like 6He Jp= 0+, S1n=1.87 MeV, S2n=0.97 MeV, T1/2=0.807 s M.V. Zhukov et al, Phys. Rep. 231 (1993) 151

  4. Introduction: 6He induced reactions before our campaign: • elastic scattering on different targets • two-neutron transfer reaction 4He(6He,a) • break-up reactions • suppression or enhancement of 6He-induced fusion? • … • what happens when another particle is added to such an loose object? • would “nuclear molecules” be formed?

  5. Introduction: nuclear molecules similar to atomic case: • two strongly bound inert cores (e.g. a-particles) • weak attractive potential that becomes repulsive at small distances • weakly bound single-particle orbits of valence particles • large transfer probability of valence particles essential difference: • mass of valence particles (electrons vs. nucleons) • equality of valence particles and parts of cores (identical nucleons  Pauli principle!) W.von Oertzen Z.Phys. A354 (1996) 37 W.von Oertzen et al, Phys. Rep. 432 (2006) 43

  6. Nuclear molecules: experimental signatures • production reaction mechanism: cluster transfers preferred • decay reduced widths: large for cluster decay • “resonant particle decay spectroscopy”: production of the state of interest and its sequential decay • rotational bands (deformed quantum objects can rotate!) • strong gamma-transitions within members of band • parity splitting wave function overlap “complete” spectroscopy!

  7. Louvain-la-Neuve RNB facility • two cyclotrons • primary beam: protons at 30 MeV - intensity: 0.5 mA (15 kW at target!) • production reaction: 7Li(p,2p)6He

  8. Louvain-la-Neuve RNB facility • two cyclotrons • primary beam: protons at 30 MeV - intensity: 0.5 mA (15 kW at target!) • production reaction: 7Li(p,2p)6He • 6He extracted and purified with electric / magnetic fields and chemical traps (as fast as possible) • secondary beam (6He): - energy: 5-70 MeV - intensity: up to 106 - 107 pps (≈ pA) - only impurity: HeH2

  9. Detectors • silicon strip detectors • different configurations developed in collaboration with Micron Semiconductors Ltd. • modular design allows different geometries • dimensions: up to 5cm x 5cm, thickness 20-1000 mm T. Davinson et al, Nucl.Instrum.Meth. A454 (2000) 544

  10. Detector set-ups • small intensity of RNBs  large solid angle covered • 20 sectors with 16 silicon strip-detectors, grouped into 3 arrays: - LEDA (4-12 deg) - LAMP1 (20-65 deg) - LAMP2 (115-160 deg) 6He+6,7Li,9Be,12C

  11. Detector set-ups • small intensity of RNBs  large solid angle covered • CD – 40 mm thick DE detector segmented into 4x16 strips • PAD – 500 mm thick E detector segmented into 4 quadrants 6He+1,2H,12,14C,16O FC T CD/PAD LEDA LAMP

  12. Experimental results • elastic and inelastic scattering on 6Li, 7Li,9Be, 12C and 19F • large cross sections for 6He induced a-particle pick-up to some 10Be states • first results for the (6He,8Be) two-proton pick-up reactions on 9Be, 12C, 16O and 19F • (6He,a) transfer reactions studied on 6Li, 7Li,9Be, 12C and 19F • widths, spins and parities for several 10Be states • decay mode for 9Be, 10Be, 11Be and 14C states • quasi-free scattering of 6He on deuteron in 6Li and on a-particle in 9Be • production of 10-12B by fusionin 6He+6Li and 6He+7Li reactions • …

  13. Transfer reactions: (6He,8Be) • 8Begs= 2a+93 keV: unique signature  simple extraction • other advantages: 0+, Q-values, wave-function overlaps,… • clearly observed on the 12C (clearly direct!), 16O and 19F (populating many states in 10Be, 14C and 17N) M.Milin et al, Phys.Rev. C70 (2004) 044603

  14. 6He a 10Be 6He 2H 6Li Sequential decay reactions • several 10Be states seen in 6,7Li(6He, 10Be* 6Hea)3,2H reaction

  15. Results for 10Be: resonant elasticscattering • with 4He gas target: 6He+4He  10Be* 6He+4He • the 10.15 MeV state again the strongest Ex=10.2 MeV Jp=4+ M.Freer et al, Phys.Rev.Lett. 96 (2006) 042501

  16. Results for 10Be known 0+ intruder state at Ex= 6.18 MeV rotational band 2+ state at Ex= 7.54 MeV • extreme deformation! • moment of inertia >2.5 times larger than for already deformed 10Be ground state band • very strong in a-transfer • observed a-decay  large a-reduced width state at Ex= 10.15 MeV • the strongest peak in 6He+a coincidences • Jp=4+ assignment favoured NUCLEAR MOLECULE! M.Milin et al, Nucl.Phys. A753 (2005) 263 M.Freer et al, Phys.Rev.Lett. 96 (2006) 042501

  17. Results for 10Be known 0+ intruder state at Ex= 6.18 MeV 2+ state at Ex= 7.54 MeV • very strong in a-transfer • observed a-decay  large a-reduced width state at Ex= 10.15 MeV • the strongest peak in 6He+a coincidences • Jp=4+ assignment favoured M.Milin et al, Nucl.Phys. A753 (2005) 263 M.Freer et al, Phys.Rev.Lett. 96 (2006) 042501

  18. Theory: 10Be Y.Kanada-En'yo et al, Phys. Rev. C 60 (1999) 064304

  19. Fusion of halo nuclei around barrier • Catania/Edinburgh/LLN/Zagreb collaboration:6He+64Zn in LLN fusion cross section NOT enhanced! reaction cross section enhanced

  20. Nuclear molecules: list of experiments • ... • 7Li+7Li (Zagreb ‘94) • 7Li+9Be, 7Li+11B (Catania, ‘96) • 6He+6Li (Louvain-la-Neuve, ‘98) • 6He+6Li, 6He+7Li, 6He+12C (Louvain-la-Neuve, ‘99) • 7Li+7Li (Zagreb ‘99) • 18O+9Be (Catania, ‘00) • 13C+9Be (Catania, ‘02) • 6He+14C, 6He+9Be (Louvain-la-Neuve, ‘05) • … + in collaboration with Berlin group: 14N+10Be, 7Li+9Be, 18O+13C, 12C+12C, 12C+13C, 12C+14C, 7Li+12-14C, ... + in collaboration with Birmingham group: 9Be+7Li, 7Li+7Li, 10Be+12C, 18O+12C, 13C+14C, 18O+9Be, 12Be+12C, 6He+4He, ...

  21. IRB-experiments: 10.15 MeV state in 10Be • Zagreb: 7Li(7Li,6Hea)4He at 8 MeV • decay mode: alpha-particle emission • 10.6 MeV state: decays by neutron emission N. Soić et al, Europhys. Lett. 34 (1996) 7

  22. Conclusions and outlook • different reactions measured with 6He radioactive beam: 6He+1,2H,4He,6,7Li,9Be,12,14C,16O • clustering in 8Li, 9Be, 10Be, 11Be, 14C studied • (partial) angular distributions obtained for different transfer reactions, some data still under analysis • (part of) future work of Zagreb group: 7Be induced reactions! DSSSD 7Be+6,7Li approved in LLN, to be measured in automn 2008 FC T DSSSD

  23. ISOLDE, CERN 11/06 property of the Huelva group

  24. Collaborators • Ð.Miljanić, S. Blagus, D.Jelavić, N.Soić, M.Uroić, M.Zadro, Ruđer Bošković Institute, Zagreb, Croatia; • M.Majer, University of Zagreb, Zagreb, Croatia; • C.Angulo, E.Casarejos, N.de Sereville,A.M.Sánchez-Benitez, Institut de Physique Nucléaire, Université Catholique de Louvain, Louvain-la-Neuve, Belgium; • S.Cherubini, A.Di Pietro, P.Figuera, M.Lattuada, A.Maggio, A.Musumarra, M.G.Pellegriti, C.Spitaleri, LNS, INFN, Catania, Italy; • T.Davinson, A.N.Ostrowski, A.C.Shotter, University of Edinburgh, Edinburgh, Great Britain; • N.Ashwood, N.Curtis, M.Freer, D.Price, V.Ziman, University of Birmingham, Birmingham, United Kingdom; • L.Acosta, M.A.G.Alvarez, I.Martel. Universidad de Huelva, Huelva, Spain

  25. Introduction

  26. 6He+1H • elastic scattering, two neutron transfer

  27. Quasi-free scattering • 6He quasi-free scattering off d- and a-clusters in 6Li observed, and not observed for the case of 7Li (L=0 for a-d in 6Li and L=1 for a-t in 7Li) d2s12 d3s  ~ k.f. |f(q)|2 dW dEdW1dW2 Ð.Miljanićet al, to be published

  28. Fusion • strong contribution from the xLi+a coincidences observed (in both 6He+6Li and 6He+7Li) • peaks corresponding to the 10-12B states identified…

  29. Fusion of halo-nuclei around the barrier • the influence of halo structure on reaction mechanism around the Coulomb barrier • theory: 1)fusion probability enhancedbecause weakly bound neutrons effectively reduces the barrier animation taken from:http://fys.kuleuven.be/iks/lisol/research/fusion/6hefusion_generalpub.htm

  30. Fusion of halo-nuclei around the barrier • the influence of halo structure on reaction mechanism around the Coulomb barrier • theory: 2)fusion suppresseddue to projectile break-up animation taken from:http://fys.kuleuven.be/iks/lisol/research/fusion/6hefusion_generalpub.htm

  31. Fusion of halo-nuclei around the barrier • the influence of halo structure on reaction mechanism around the Coulomb barrier • theory: 3)fusion probability enhancedbecause weakly bound projectiles tunnels animation taken from:http://fys.kuleuven.be/iks/lisol/research/fusion/6hefusion_generalpub.htm

  32. Fusion of halo-nuclei around the barrier • First results: 6He+209Bi - J.J.Kolata et al., Phys.Rev.Lett. 81 (1998) 4580 6He+238U – M.Trotta et al., Phys.Rev.Lett. 84 (2000) 2342 ...  • reaction cross sectionenhanced • fusion cross sectionenhanced • transfer cross sectionslarge • break-up cross sectionslarge

  33. Fusion of halo-nuclei around the barrier • Catania/Edinburgh/LLN/Zagreb collaboration:6He+64Zn in LLN fusion cross section NOT enhanced! A.Di Pietro et al.,Europhys.Lett. 64 (2003) 309 A.Di Pietro et al., Phys. Rev. C69 (2004) 044613

  34. Fusion of halo-nuclei around the barrier • Catania/Edinburgh/LLN/Zagreb collaboration:6He+64Zn in LLN The same results for6He+238U R.Raabe et al., Nature 431 (2004) 823 fusion cross section NOT enhanced! reaction cross section enhanced

  35. Elastic and inelastic scattering • fair agreement with optical model predictions, using the 6Li –potentials • half of 15% enhancement for the 12C target due to the Borromean structure of 6He (Matsumoto et al., PRC 70, 061601) • inelastic scattering observed only for the first excited state of 12C and 9Be M.Milin et al, Nucl. Phys. A730 (2004) 285 M.Milin et al, Nucl. Phys. A746 (2004) 183

  36. Elastic and inelastic scattering • 6He+9Be @ 17 MeV • only inelastic peak corresponds to the 2.45 MeV state • different states seen in the 9Be(6He,a)11Be reaction, still under analysis 6He+9Be 17 MeV elastic inelastic analysis by Marija Majer

  37. Transfer reactions • large solid angle  large efficiency for detecting coincidences  partial angular distributions: • 1H(6He,a)3H • 6Li(6He,a)8Li • 6Li(6He,t)9Be • 6Li(6He,d)10Be • 7Li(6He,a)9Li • 7Li(6He,t)10Be • 12C(6He,a)14C • … M.Milin et al, Nucl. Phys. A746 (2004) 183

  38. Transfer reactions: 6He+6Li a+8Li • direct transfers of 2n and d allow comparison of the a+2n configuration in 6He with the a+d configuration in 6Li • spectroscopic factors equal within 10% • more complete angular distributions needed! 2-mode DWBA M.Milin et al, Phys.Atom.Nucl. 69 (2006) 1360

  39. Results for 10Be: transfer reactions • 6Li and 7Li: a-cluster structure  ideal targets for a-pickup • large cross sections for a-transfer to some high-excited 10Be states observed  at least one of the states of the doublet at ≈7.5 MeV shows strong a-clustering M.Milin et al, Europhys.Lett. 48 (1999) 616 and to be published

  40. Sequential decay reactions • triple coincidences 6He+12C g10Be+2a • strong peaks corresponding to 10Be g.s., 2+ and groups of states at ≈ 6.0 and ≈ 7.5 MeV seen • cluster states in 14C reconstructed – no strong selectivity • problems with the 14C target  16C spectrum not clean 16C M.Milin et al, Nucl.Phys. A730 (2004) 285 and Eur.Phys.J. A, accepted

  41. 10.15 MeV state in 10Be • 9Be(n,a)6He reaction (3.3 – 6.1 MeV): “weakresonances for En=3.73 and 4.27 MeV(Ex=10.15 and 10.65 MeV in 10Be)” • The data has never been published!

  42. 10.15 MeV state in 10Be • Dubna: 7Li(7Li,a)10Be reaction at 30 MeV • A.A. Ogloblin et al., Heidelberg conference '69

  43. 10.15 MeV state in 10Be • Tokyo: 7Li(a,p)10Be reaction at 65 MeV • S.Hamada et al, Phys. Rev. C 49 (1994) 3192

  44. 10.15 MeV state in 10Be • FSU: 7Li(7Li,6Hea)4He and 6Li(7Li,6Hea)3He at 34 MeV • same experiment: - first observation of the a-decay of the 2+ state at Ex= 7.54 MeV; - decay energy only 129 keV  very large reduced width! N. Curtis et al, Phys. Rev. C 64 (2001)044604

  45. 10.15 MeV state in 10Be • Catania: 7Li+7Li and 7Li+9Be at 30 MeV Decay:  + 6He(0+)  + 6He(2+)  + 6He(0+) Đ. Miljanić et al, Fizika B 10 (2001) 235

  46. Other A=10 nuclei: 10B and 10C • 10Be: rotational band of very deformed states established! • analogue states in 10B and 10C?

  47. 10B • Zagreb: p+9Be excitation functions from 5.5-9.5 MeV diploma thesis D.Jelavić

  48. 10B • Zagreb: p+9Be excitation functions from 5.5-9.5 MeV diploma thesis D.Jelavić

  49. 10B • Zagreb: p+9Be excitation functions from 5.5-9.5 MeV diploma thesis D.Jelavić

  50. 10B • Zagreb: p+9Be excitation functions from 5.5-9.5 MeV diploma thesis D.Jelavić

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