A1260947860zypNR

1
Reactions induced by low energy 6He beam
Matko Milin
Faculty of Science, University of Zagreb, Croatia
S.Blagus, D.Jelavic, Ð.Miljanic, N.Soic, M.Uroic,
M.Zadro Ruder Boškovic Institute, 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, S1n1.87 MeV, S2n0.97 MeV,
T1/20.807 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)

6He6,7Li,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

6He1,2H,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 6He6Li and
  6He7Li reactions

13
Transfer reactions (6He,8Be)

• 8Begs 2a93 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
Sequential decay reactions

• several 10Be states seen in 6,7Li(6He, 10Be ?
  6Hea)3,2H reaction

15
Results for 10Be resonant elastic scattering

• with 4He gas target 6He4He ? 10Be ? 6He4He
• the 10.15 MeV state again the strongest

Ex10.2 MeV
Jp4
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 gt2.5 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 6Hea coincidences
• Jp4 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 6Hea coincidences
• Jp4 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
  6He64Zn in LLN

fusion cross section NOT enhanced!
reaction cross section enhanced
20
Nuclear molecules list of experiments

• ...
• 7Li7Li (Zagreb 94)
• 7Li9Be, 7Li11B (Catania, 96)
• 6He6Li (Louvain-la-Neuve, 98)
• 6He6Li, 6He7Li, 6He12C (Louvain-la-Neuve,
  99)
• 7Li7Li (Zagreb 99)
• 18O9Be (Catania, 00)
• 13C9Be (Catania, 02)
• 6He14C, 6He9Be (Louvain-la-Neuve, 05)
• in collaboration with Berlin group 14N10Be,
  7Li9Be, 18O13C, 12C12C, 12C13C, 12C14C,
  7Li12-14C, ...
• in collaboration with Birmingham group
  9Be7Li, 7Li7Li, 10Be12C, 18O12C, 13C14C,
  18O9Be, 12Be12C, 6He4He, ...

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. Soic et al, Europhys. Lett. 34 (1996) 7
22
Conclusions and outlook

• different reactions measured with 6He
  radioactive beam 6He1,2H,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
7Be6,7Li 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.Miljanic, S. Blagus, D.Jelavic, N.Soic,
  M.Uroic, M.Zadro, Ruder Boškovic 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
6He1H

• 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 (L0 for a-d in 6Li and L1 for a-t in 7Li)

d2s12
d3s
?
k.f. f(q)2
dW
dEdW1dW2
Ð.Miljanic et al, to be published
28
Fusion

• strong contribution from the xLia coincidences
  observed (in both 6He6Li and 6He7Li)
• 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 http//fys.kuleuven.be/ik
s/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 suppressed due to projectile break-up

animation taken from http//fys.kuleuven.be/ik
s/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 enhanced because weakly
  bound projectiles tunnels

animation taken from http//fys.kuleuven.be/ik
s/lisol/research/fusion/6hefusion_generalpub.htm
32
Fusion of halo-nuclei around the barrier

• First results
• 6He209Bi - J.J.Kolata et al., Phys.Rev.Lett. 81
  (1998) 4580
• 6He238U 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
  6He64Zn 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)
044613
34
Fusion of halo-nuclei around the barrier

• Catania/Edinburgh/LLN/Zagreb collaboration
  6He64Zn in LLN

The same results for 6He238U 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

• 6He9Be _at_ 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

6He9Be 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 6He6Li ? a8Li

• direct transfers of 2n and d allow comparison of
  the a2n configuration in 6He with the ad
  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 6He12C g 10Be2a
• 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
(Ex10.15 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 7Li7Li and 7Li9Be at 30 MeV

Decay
? 6He(0)
? 6He(2)
? 6He(0)
Ð. Miljanic et al, Fizika B 10 (2001) 235
46
Other A10 nuclei 10B and 10C

• 10Be rotational band of very deformed states
  established!
• analogue states in 10B and 10C?

47
10B

• Zagreb p9Be excitation functions from 5.5-9.5
  MeV

diploma thesis D.Jelavic
48
10B

• Zagreb p9Be excitation functions from 5.5-9.5
  MeV

diploma thesis D.Jelavic
49
10B

• Zagreb p9Be excitation functions from 5.5-9.5
  MeV

diploma thesis D.Jelavic
50
10B

• Zagreb p9Be excitation functions from 5.5-9.5
  MeV

diploma thesis D.Jelavic
51
10B

• Zagreb 11B(3He,aa)6Li at 15 MeV

analysis by M.Uroic
52
10B

• Zagreb 11B(3He,aa)6Li at 15 MeV

preliminary
analysis by M.Uroic
53
10B and 10C
7Li7Li ? a10Be ? a?6He
6Li7Li ? 3He10Be ? 3He?6He
N.Curtis et al, Phys.Rev.C 64 (2001) 044604
7Li7Be ? a10B (T1) ? aa6Li (T1)
approved in LLN
new results on 10C, talk by N.Curtis,
Tuesday 1700
3He10B (T1) ? 3He?6Li (T1)
6Li7Be
t10C ? t?6Be ? t??2p
54
Sequential decay reactions

• triple coincidences observed 6He6Li g
  6Head 6He7Li g 6Heat 6He6Li g 2atn
  6He12C g 10Be2a

(double coincidences not enough!)
6He6Li g 2atn

• 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 5Hea?)

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 2001.
• the 10.15 MeV state is always the strongest peak
  in the 6Hea coincidences

M.Milin et al, Nucl.Phys. A753 (2005) 263
56
6He6Li ? 10Bed ? 6He6Lid

• 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 Jp4

M.Milin et al, Nucl.Phys. A753 (2005) 263