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 Bošković Institute, Zagreb, Croatia

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

3. Jp= 0+, S1n=1.87 MeV, S2n=0.97 MeV, T1/2=0.807 s
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 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 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 ( 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 fusion in 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)

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

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

16. known 0+ intruder state at Ex= 6.18 MeV
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= 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)

17. known 0+ intruder state at Ex= 6.18 MeV
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= 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)

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

19. fusion cross section NOT enhanced! reaction cross section enhanced
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. 7Be+6,7Li approved in LLN, to be measured in automn 2008
Conclusions and outlook
different reactions measured with 6He radioactive beam: He+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 T FC
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. Ð.Miljanić et al, to be published
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)
d3s
d2s12
~ k.f. |f(q)|2 
dEdW1dW2 dW
Ð.Miljanić et 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 enhanced because weakly bound neutrons effectively reduces the barrier
animation taken from:

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

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:

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 section enhanced
fusion cross section enhanced
transfer cross sections large
break-up cross sections large

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. C 69 (2004)

34. Fusion of halo-nuclei around the barrier
Catania/Edinburgh/LLN/Zagreb collaboration: 6He+64Zn in LLN
The same results for 6He+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, )
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
17 MeV
only inelastic peak corresponds to the 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. and Eur.Phys.J. A, accepted
Sequential decay reactions
triple coincidences 6He+12C g 10Be+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):
“weak resonances for En= 3.73 and 4.27 MeV (Ex=10.15 and 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

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

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

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

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

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

56. 6He+6Li  10Be*+d  6He+6Li+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 Jp=4+
10Be, Ex= MeV, J = 4+
M.Milin et al,
Nucl.Phys. A753 (2005) 263