Exploring the 10Li structure by the d(9Li,p)10Li transfer reaction

Manuela CavallaroINFN – LNS (Italy)

• In weakly bound or unbound neutron-rich nuclei, the scale of the neutron binding energy goes down to few hundreds keV

• Residual interactions must be treated to that level of accuracy

Investigation of light exotic nuclei

Thus the study of light neutron rich nuclei is an important tool to test microscopic theories of nuclear structure

The 10Li nucleus

Provides constraints to describe the n + 9Li interaction Crucial ingredient for the description of the 2n halo nucleus 11Li

The structure of the unbound ground and low-lying excited states remains unclear (Ex, Jπ, Γ are still controversial)

The 10Li nucleus

1s1/2

1p3/2 9Li3/2- core

1p1/2

p n

2s1/2

2+/1+ and 2-/1- doublets are expected among the low-lying states

It is no clear which one is the g.s. and what are the excited states

10Li ground state

10Li 11Be 13C12B 14N 15O2s1/2

1p1/2

1d5/2

N = 7 isotones

The 10Li nucleus

1s1/2

1p3/2 9Li3/2- core

1p1/2

p n

2s1/2

Esperimental difficulties:

• Far from stability → it requires the transfer of at least 3 nucleons on a stable target (heavy-ion stable beams) OR use of RIBs in inverse kinematics

• Odd-odd nucleus → large number of excited states

• Particle unstable in the g.s. → states involving 2s1/2 config. are very broad and difficult to be observed in the presence of a 3-body continuum

H.G.Bohlen, et al., Z. Phys. A 344 (1993) 381 Nucl. Phys. A 616 (1997) 254 Progr. Part. Nucl. Phys. 42 (1999) 17

Previous studies

HI multinucleon transfer reactions

selectivity for final states due to different starting configurations and probes

Low statistics and large background

Strength distributions for different angular momentum of the neutron:Strong p1/2 resonance at low energy s1/2 shows a non-resonant contribution

H.G.Bohlen, et al., Z. Phys. A 344 (1993) 381Previous studies

Mean fied calculations including pairing:

RPA calculations: Including the residual interactions of the unbound neutron with the 9Li-system (dynamical correlations due to the p-n interactions)

Conclusions based only

on the position and

shape of peaks

Not supported by any angular distributions

Light-ion induced reactions d(9Li,p)10Liare the best tools (long tradition of applications)

give the clearest measurement of the transferred

Ideal to probe the single particle degrees of freedom of the residual states wave function

9Li and the recoiling protons coincidence measurements minimize the contributions due to excitation of 11Be compound nucleus

Previous studies of d(9Li,p)10Li reaction

intensity 7 10∙ 3 pps 100 counts integrated up to ~5 MeVLow energy resolution ( 700 keV)

P. Santi et al. PRC 67 (2003) 024606

0.33 MeV

the results were not very conclusive, due to poor statistics and the question of the possible presence

of a low-lying virtual state in 10Li remains open

intensity 5 10∙ 4 pps 100 counts integrated

H.B. Jeppesen et al. PLB 677 (2006) 449

2.4 MeV/u

20 MeV/u

Our d(9Li,p)10Li experiment

• 9Li incident energy @ 11.13 MeV/u delivered by ISACII

• Intensity 5 10∙ 5 pps (FC and checked by Rutherford elastic scattering)

• Excellent beam emittance and thin target (CD2 126 μg/cm2) -> high resolution in 10Li energy spectrum and angular distributions

• Angular distributions at forward angles

Experimental setupTUDA - The TRIUMF UK Detector Array

127° < θ < 152° 1° < θ < 3°

np

9Li9Li beam

LEDA S2CD2 target

126 μg/cm2

LEDA system:Louvain-Edinburgh Detector ArrayT. Davinson et al.: NIM A 454 (2000) 350-358

•8 sectors x 16 strips•Good energy resolution and low detection thresholds•Large area -> Large solid angle coverage•High segmentation -> good angular resolution

S2:double sided annular silicon detectors

Recoiling protons Outgoing 9Li from the 10Li BU

∆E-E Telescope for PID and trigger

An additional benefit to placing the proton detectors at backward scattering angles is that no background was expected from other reactions between the beam and the target. In all these cases, the kinematics of the reaction are insufficient to produce a light nucleus at backward scattering angles.

Experimental setupKinematics of the outgoing d and p for the 9Li+d and 9Li+p reactions

Angular range covered by LEDA

10Li excitation energy

~ 9000 counts integrated up to 4.5 MeV excitation energy

~ 200 keV energy resolution (FWHM)

No evidence of the virtual state at negative energy used by Jeppesen to explain the strenght at zero excitation energy

7.5° < θCM < 16.5°at Ex = 0.6 MeV

Ex = Q0 - Q (MeV)

10Li excitation energy

E0 = 0.60 ± 0.03 MeVΓ = 0.67 ± 0.03 MeV E0 = 1.4 ± 0.1 MeV

Γ = 0.8 ± 0.2 MeV

S n(9 Li +

n) =

-0.0

25 M

eV

Ex = Q0 - Q (MeV)

7.5° < θCM < 16.5°at Ex = 0.6 MeV

Comparison with theoryS.E.A.Orrigo and H.Lenske PLB 677 (2009) 214

Description of 10Li in an extended mean-field approach including n-n pairing correlations in the continuum to all orders (full HFB Gorkov approach)

However:

The coupling with the p3/2 proton orbital is not present, it should generate multiplets

The 9Li core is inert (E*(9Li) = 2.69 MeV)

These dynamical correlations due the treatment of paring give rise to sharp low-lying resonances close to the particle emission threshold which

are no present in the bare Mean Field approach

p3/2

p1/2

s1/2

d5/2

d2 σ/d

EdΩ

[mb/

sr M

eV]

θCM [deg]

The structure results are used as input for transfer cross-section calculations (DWBA, Vincent and Fortune technique)

Optical potential: Hinterberger deuteron OMP in the incident channel (d + 9Li)Menet proton potential in the exit channel (p + 10Li)

The best angular region to disentangle the different partial-wave contributions

Explored by Jeppesen et al.

S.E.A.Orrigo and H.Lenske PLB 677 (2009) 214Comparison with theory

10Li excitation energy spectrum

d(9Li,p)10Li7.5° < θCM < 16.5°

Angular distributions

The measured angular distribution is well described by the p1/2 component

both in shape and absolute cross-sectionpreliminary

Angular distributionsThe 1.4 MeV peak does not

appear in the calculated excitation energy spectrum

Only the s1/2 well reproduce the experimental slope

Missing s1/2 strength due to lack of neutron-proton

interactionpreliminary

Angular distributionsThe contribution of the

d5/2 configurations starts to be important

Structure at the same energy interpreted as d-wave by Bohlen(d-wave contribution important also in Blanchon et al., NPA 791

(2007) 303)

Limitation in the model (9Li inert core)preliminary

Conclusions1) The 10Li spectrum has been measured for the first time up to 4.5 MeV excitation energy by the d(9Li,p)10Li reaction at 11.13 AMeV

2) The spectrum shape at the neutron emission threshold likely excludes a strong contribution from a s1/2 virtual state

3) At least 3 structures have been identified and the absolute cross-section angular distributions have been extracted

4) 0.6 MeV peak → p1/2 configuration

6) Next step is to perform more refined calculations including n-p interaction (doublets) and core-excitations

5) 1.4 MeV peak → s1/2 configuration (according to Bohlen et al.)

Conclusions

C. Agodi, M. Bondì, D. Carbone, F. Cappuzzello, M. Cavallaro, A. Cunsolo, B. Davids, T. Davinson, M. De Napoli, A. Foti, N. Galinski,

R. Kanungo, H. Lenske, S.E.A. Orrigo, C. Ruiz, A. Sanetullaev

INFN, Laboratori Nazionali del Sud, ItalyINFN, Sezione di Catania, Italy

Dipartimento di Fisica e Astronomia, Università di Catania, ItalyTRIUMF, Vancouver, Canada

Department of Physics and Astronomy, University of Edinburgh, UKSaint Mary’s University, Canada

Institut fur Theoretische Physik, Universitat Gießen, GermanyInstituto de Física Corpuscular, CSIC-Universidad de Valencia, Spain

Collaboration

Thank you

Theoretical predictions

Comparison: full HFB Gorkov-pairing (blue) and bare MF calculations (red)• Pairing gives an attractive self-energy in the p-wave channels → 1/2– and

3/2– resonances at very low energy• Slight attraction in the 1/2+ channel and repulsion for the d-waves

S.E.A.Orrigo and H.Lenske PLB 677 (2009) 214

p3/2

p1/2

s1/2

d5/2

Partial wave cross-sections for elastic scattering of n on 9Li

Description of the 10Li in an extended mean-field approach including n-n pairing correlations in the continuum to all orders

The coupling with the p3/2 proton orbital should generate multiplets

Excitation energy resolution

• ΔE = 30 keV (LEDA proton kinetic energy resolution) alpha-source

• Δθ = 1° (LEDA angular resolution)

• Beam spot 2mm

• Kinematics

I. J. Thompson and M. V Zhukov, Phys. Rev. C 49 (1994) 1904Previous studies

(s1/2)2 3%, (p1/2)2 97% (s1/2)2 45%, (p1/2)2 51% (s1/2)2 97%, (p1/2)2 1%

The presence of a s1/2 virtual state is crucial in order to reproduce the

momentum distributions in 11Li fragmentation

N. Orr, et al., Phys. Rev. Lett. 69 (1992) 2050