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

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Presentation on theme: "Matko Milin Faculty of Science, University of Zagreb, Croatia Reactions induced by low energy 6 He beam S.Blagus, D.Jelavić, Ð.Miljanić, N.Soić, M.Uroić,"— Presentation transcript:

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

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

3 Introduction: 6 He structure Borromean structure two loosely bound neutrons orbiting an -core large interaction radius! R RMS 2.5 fm vs. R RMS ( ) 1.7 fm components: di-neutron and cigar-like M.V. Zhukov et al, Phys. Rep. 231 (1993) He J = 0 +, S 1n =1.87 MeV, S 2n =0.97 MeV, T 1/2 =0.807 s

4 Introduction: 6 He induced reactions before our campaign: elastic scattering on different targets two-neutron transfer reaction 4 He( 6 He, ) break-up reactions suppression or enhancement of 6 He-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. -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 complete spectroscopy! wave function overlap

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

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

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 m 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 ( deg) 6 He+ 6,7 Li, 9 Be, 12 C

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

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

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

14 6 He 10 Be 6 He 6 Li 2H2H Sequential decay reactions several 10 Be states seen in 6,7 Li( 6 He, 10 Be* 6 He ) 3,2 H reaction

15 Results for 10 Be: resonant elastic scattering E x =10.2 MeV J =4 + with 4 He gas target: 6 He+ 4 He 10 Be* 6 He+ 4 He the MeV state again the strongest M.Freer et al, Phys.Rev.Lett. 96 (2006)

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

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

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

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

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

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

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 6 He+ 1 H elastic scattering, two neutron transfer

27 Quasi-free scattering 6 He quasi-free scattering off d- and -clusters in 6 Li observed, and not observed for the case of 7 Li (L=0 for - d in 6 Li and L=1 for -t in 7 Li) Ð.Miljanić et al, to be published d 3 dEd 1 d 2 ~ k.f. | (q)| 2 d 2 12 d

28 Fusion strong contribution from the x Li+ coincidences observed (in both 6 He+ 6 Li and 6 He+ 7 Li) peaks corresponding to the B states identified…

29 the influence of halo structure on reaction mechanism around the Coulomb barrier theory: 1) fusion probability enhanced because weakly bound neutrons effectively reduces the barrier Fusion of halo-nuclei around the barrier animation taken from: b.htm

30 Fusion of halo-nuclei around the barrier animation taken from: b.htm the influence of halo structure on reaction mechanism around the Coulomb barrier theory: 2) fusion suppressed due to projectile break-up

31 Fusion of halo-nuclei around the barrier the influence of halo structure on reaction mechanism around the Coulomb barrier theory: 3) fusion probability enhanced because weakly bound projectiles tunnels animation taken from: b.htm

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

33 Catania/Edinburgh/LLN/Zagreb collaboration: 6 He+ 64 Zn in LLN fusion cross section NOT enhanced! A.Di Pietro et al., Europhys.Lett. 64 (2003) 309 A.Di Pietro et al., Phys. Rev. C 69 (2004) Fusion of halo-nuclei around the barrier

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

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

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

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

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

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

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

41 10.15 MeV state in 10 Be The data has never been published! weak resonances for E n = 3.73 and 4.27 MeV (E x =10.15 and MeV in 10 Be) 9 Be(n, ) 6 He reaction (3.3 – 6.1 MeV):

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

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

44 10.15 MeV state in 10 Be FSU: 7 Li( 7 Li, 6 He ) 4 He and 6 Li( 7 Li, 6 He ) 3 He at 34 MeV same experiment: - first observation of the -decay of the 2 + state at E x = 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 10 Be Catania: 7 Li+ 7 Li and 7 Li+ 9 Be at 30 MeV Đ. Miljanić et al, Fizika B 10 (2001) He(0 + ) Decay: + 6 He(2 + ) + 6 He(0 + )

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

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

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

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

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

51 10 B Zagreb: 11 B( 3 He, ) 6 Li at 15 MeV analysis by M.Uroić

52 10 B Zagreb: 11 B( 3 He, ) 6 Li at 15 MeV preliminary analysis by M.Uroić

53 10 B and 10 C 6 Li+ 7 Li 3 He+ 10 Be* 3 He+ + 6 He 6 Li+ 7 Be 3 He+ 10 B* (T=1) 3 He+ + 6 Li (T=1) t+ 10 C* t+ + 6 Be t+ + +2p 7 Li+ 7 Be + 10 B* (T=1) + 6 Li (T=1) 7 Li+ 7 Li + 10 Be* He N.Curtis et al, Phys.Rev.C 64 (2001) approved in LLN new results on 10 C, talk by N.Curtis, Tuesday 17:00

54 M.Milin et al, Nucl.Phys. A753 (2005) 263 triple coincidences observed: 6 He+ 6 Li 6 He+ +d 6 He+ 7 Li 6 He+ +t 6 He+ 6 Li 2 +t+n 6 He+ 12 C 10 Be+2 decay and structure of some 9 Be and 14 C states studied peak in 8 Be excitation spectrum at 0.5 MeV: decay of the 2.45 MeV state in 9 Be through the 8 Be*(2 + )+n channel (or 5 He+ ?) (double coincidences not enough!) Sequential decay reactions 6 He+ 6 Li 2 +t+n

55 Results for 10 Be: sequential decay reactions several 10 Be states seen in 6,7 Li( 6 He, 10 Be* 6 He ) 3,2 H reaction large reduced width for -decay found for the 2 + state at E x = 7.54 MeV; agrees with the results of Liendo et al, Phys. Rev. C the MeV state is always the strongest peak in the 6 He+ coincidences M.Milin et al, Nucl.Phys. A753 (2005) 263

56 6 He+ 6 Li 10 Be*+d 6 He+ 6 Li+d angular correlations between the decay products can be used to assign spin and parity of the state that decays (if the decay products have J = 0 + ) Monte Carlo simulations compared with the exp. results strongly favour J = Be, E x = MeV, J = 4 + M.Milin et al, Nucl.Phys. A753 (2005) 263


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