Reaction experiments induced by light exotic nuclei at REX-

ISOLDE

Olof TENGBLADInstituto de Estructura de la Materia

Consejo Superior de Investigaciones CientíficasMadrid Spain

Madrid-Aarhus-Göteborg

Probing the halo @ REX

•IS367 P100 Study of the unbound nuclei 10Li and 7He at REX ISOLDE•IS371 P105 Investigations of neutron-rich nuclei at the dripline through their analogue states: The cases of 10Li-10Be (T=2) and 17C-17N (T=5/2)•IS399 P134 Exploring the dipole polarizability of 11Li at REX-ISOLDE •IS430 P187 Study of neutron-rich Be isotopes with REX-ISOLDE

• The first run took place September 2005. Beam energy 2.25 MeV/u, thin stripper foil to reduce the amount of 22Ne. Two DSSSD (32 by 32 strips) backed by 1.5 mm Si in the forward direction, monitor telescope in beam dump behind reduction foil. Targets: deuterated polyethylene and standard polyethylene, Ag for normalization.

• The second run took place October 2009. The MINIBALL with the T-REX chamber were used. Beam energy 2.85 MeV/u. Targets: Deuterated polyethylene, polyethylene, Ag, carbon and aluminum.

• The third run (remaining 18 shifts) took place September 2010. Same configuration, beam energy and targets as October 2009. Mainly runs with 15 mm collimator, a few with 5 mm.

•IS438 P192 Elastic scattering and fusion studies in the reactions 10,11Be+64Zn A. Di Pietro, Catania•IS444 P206 Exploring halo effects in the scattering of 11Be on heavy targets at REX-ISOLDE•IS446 P211 Investigation of the 8Li(2H,p)9Li reaction at REX-ISOLDE

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Bound lithium isotopes

11Li – a halo nucleus

6Li 7Li 8Li 9Li

mass number

nucl

ear r

adiu

s (fm

)

T1/2= 836 ms 178ms 8.5 msStable

Brief 11Li History1966 found bound 1975 1st spectroscopy C. Thibault @ CERN PS

ISOLDE intense study different decay modes n,2n,3n,t etc

1985 Tanhihata Berkeley exp 11Li is huge!1987 PG Hansen & B. Jonson 9Li core+ 2n halo

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Neutron-rich lithium isotopes

Purpose: Study the structure of neutron-rich lithium isotopes using transfer reactions.Goal: Reaction cross-sections compared with theoretical models, spectroscopic factors.

Debated

XX

XX X

5

Li103

Be104

21

0

21

23

0

693

21

0

T

T T

T

pLi

T=2

T=1

IS371

9Li

d-polyethylen

IS367Transfer reaction at low energy s-wave pickup (d-target) p-wave pickup (Be-target) Characterize the gs and 1:st exited state of the unbound nucleus 10Li

Elastic resonance scattering to investigate E, J of lowest T=2 states in 10Be analogues of gs and 1:st excited state of 10Li

Post-accelerated 2.3 MeV/u 9Li beam from REX-ISOLDE on PE, d-PE, Be, target respectively.

IS371

Probing unbound 10Li @ REX

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IS371: elastic resonance scattering 9Li+1H

Excitation Energy in 10Be [MeV]

600< p< 1200

p < 600 ms

Rutherford Bkg

EBIS gated

BeamGate

ungated

600 ms

Time arrival of event [ms]T1

HIE ISOLDE with 5 MeV/u and ACTAR would help to improve

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IS367: Nucelon transfer reaction: 9Li+2H/9Be

Nuclear Physics A738(2004)511-514Nuclear Physics A748(2005)374-392Phys.Lett B635(2006)17-22Phys.Lett B642(2006)449-454 d(9Li,10Li*)p using REX-ISOLDE

9Li+n

8

9Li + d8Li + t9Li + d10Li + p

9Li (2x105 pps) @ 2.77 MeV/u

-gs @ 25 keV , s1/2 (?)-1st excited @ 300 keV p1/2

-2nd state @ 500 keV, p1/2

proton-ion coincidences

Probing unbound 10Li @ REX

Cut-off[MeV]11 6He10 a3.5 t3.0 d2.3 p

IS446: Nucelon transfer reaction: 8Li+2H

ΔE-det. 32 x 32 strips 60 mm2x2 mm2 < 3o resolutionMaximize angular coverage

8Li REX-ISOLDE beam@ 3.15 MeV/u:

Reaction channels:

2H(8Li,p)9Li(*) – (d,p) pickup 2H(8Li,d)8Li(*) – (d,d) elastic 2H(8Li,t)7Li(*) – (d,t) stripping

E (MeV)

ΔE

(M

eV)

dσ/

dΩ

(a.

u.)

Composition of the beam

9

pt

d

a

10

Eex(7Li) Eex(8Li)

Eex(9Li)

E (MeV)

E (MeV)

E (MeV)

dσ/d

E (a

.u.)

dσ/d

E (a

.u.)

dσ/d

E (a

.u.)

Excitation-energies

Stripping triton

Pickup proton

Elastic deuteronExcitation energy spectra

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Theoretical calculations (FRESCO)

A. Moro Sevilla• Elastic scattering of 8Li (Jπ = 2+)– Optical model (parameters for d(9Li,d)9Li)– Compound contribution ~ 4 mb/sr– Reasonable potential for inelastic and (d,p) channel.

• Inelastic scattering– Coupled-channels

• Deformed Woods-Saxon potentialdeformation length 1.728 fm

DWBA calculation(Distorted Wave Born Aprox)

D potential between d & 8Li coreP potential p & 8Li + nB Binding potential 8Li + picked up n

P

B

D

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The solid and dashed lines are the CC calculations with two different deuteron potentials.

The dotted-dashed line is the CC calculation assuming a rotational model for the 8Li states, with an intrinsic quadrupole deformation length of 1.75fm.Works for elastic but failes the inelastic The rotational description is inadequate to describe the coupling between 8Li states

Elastic/inelastic: 2H(8Li,d)8Li*

Angular dependence of differential cross-sectionJoint analysis of elastic and inelastic channelsUsing DWBA and Coupled Channels CC methods

CC calculations show better agreement than DWBA, which confirms the importance of higher order effects

DWBA Couple Channels

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Pickup: 2H(8Li,p)9Li*

9Li ground state – good agreement at small scattering angles where the cross-section for transfer reactions is largest. A two-step process improves the agreement in the interval 50-90°.

Excited states in 9Li – the theoretical models give a lower reaction cross-section, can be due to compound nuclei, maybe excited states in 10Be (8Li + 2H → 10Be).

Measured angular distribution 2H(8Li,t)

7Li*

cross section compared to;DWBA dashed lineCoupled-Reaction-Channel CRC solid line

The CRC calculation reproduce the data well Confirming the importance of multi-step process in this reaction.

Stripping: 2H(8Li,t)7Li*

The overall result demonstrate that the transfer reaction remains a useful tool for investigating nuclear structure.

Careful theoretical treatment is neededAnd more examples to tune the parameters on.

The 8li + 2H reaction at REX-ISOLDEE. Tengborn et.al. Accepted Phys Rev C (2011)

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•IS444 P206 Exploring halo effects in the scattering of 11Be on heavy targets at REX-ISOLDE L. Acosta et.al. Eur. Phys. J. A 42, 461–464 (2009)

•IS430 P187 Study of neutron-rich Be isotopes with REX-ISOLDE

•IS438 P192 Elastic scattering and fusion studies in the reactions 10,11Be+64Zn A. Di Pietro et.al. Phys. Rev. Let. 105, 022701, (2010)

The same set-up was usedat one time

Transfer reactions with 11Be

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Transfer reactions with 11Be

• T. Aumann et al, PRL 84 (2000) 35 MSU, neutron-knockout• R. Palit et al, PRC 68 (2003) 034318 GSI, break-up

and others…

• Halo nucleus (also in bound excited state…)

• Cluster structures in neighbours• N=8 broken in 12Be

Knock out @ relativistic energies: 11Be to 10Be

12Be states

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11Be to 12Be

R. Kanungo et al, PLB682 (10) 391n-transfer at Triumf, 5 MeV/u

Neutron knockout establishing N=8 breaking, e.g. A. Navinet al, PRL 85(00) 266; S.Pain et al, PRL 96 (06) 032502

RIKEN exps, excited states on 12Be: H. Iwasaki et al, PLB481 (00) 7, 491 (00) 8; S. Shimoura et al, PLB 560 (03) 31;N. Imai et al, PLB 673 (09) 179

• Resolution for 10Be gamma-spectrum (preferential population to halo candidates 1- and 2- ??)

• Separation of 12Be states, check spec. factors• Search for 0- excitation in 12Be

What remains to do ?

• IS430 P187 Study of neutron-rich Be isotopes with REX-ISOLDE– Sept. 2005 – 2nd beamline– Oct. 2009 – T-REX (cut short, EBIS problems)– Sep. 2010 – T-REX (very successful run !!)

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2005 run - results

• Beam of 11Be, deuterium target, 2nd beamline

A. Moro, calculation: optical potential

Comparison of differential cross sections for elastic scattering on deuteron for 11Be(Green) and 11B(Cyan), along with an optical model calculation for the latter(blackline). The curvatures of the two diferentia lcrosssections are the same, but the one for 11Be is about a factor of three higher.

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2010: Particle ID via DE-E

2010 improved experimentT-REX and MINIBALL set-up

T-REX detectors are too thick:150 mm stops 16 MeV a no -DE E

p d t

t d p

a

2005 data

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Stripping: 11Be(d,t)10Be*

0+

2+

2+, 1-, 0+, 2-

0+

2+

2+ to 2+

2- to 2+

2+ to 0+

1- to 0+

21

10Be+t coincidencesi.e. complete kinematics

θx versus θy

22

Elastic/Inelastic: 11Be(d,d)11Be*

320 keV

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Pickup: 11Be(d,p)12Be*

511 line: 0+

2 pair production Doppler corrected

2100: 2+1 2700: 1-

1

Gamma lines in coincidence with p.

Excitation spectra

Black: TotalBrown: Bg from reactions on C

Red: 2+1

Green: 0+2

Blue: 1-1

.

Purpel: The four above combined

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Gamma-gated 12Be spectra

25

Cross sections from (d,p)

0+1 gs

2+1

1-1

11Be(d,p)12Be

Preliminary: Coupled channel calculations

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Conclusions

• Agreement between experimental data and theoretical calculations for (d,d) → the method describes the data.

• Good description of the ground state in 9Li → confidence to use the technique for more exotic nuclei where the nuclear structure is unknown.

FUTURE– Higher beam energy is needed HIE-ISOLDE.– Zero degree Spectrometer would help removing background and select channel– Upgrade of T-REX with thinner detectors lower alpha threshold– ACTAR as a development of the elastic resonance scattering method

• Letter of Intent to HIE-ISOLDE– Transfer reactions at and beyond the dripline tritium target (t,p)

• t(9Li,p)11Li d(11Li,p)12Li t(11Li,p)13Li• C-beams as next step

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Core - Collaboration

M. Alcorta1, M. Borge1, J. Byskov-Nielsen2, J. Cederkäll3, C. Diget2, L. Fraile1, H. Fynbo2, J. Gomez-Camacho4, H. Jeppesen2, H. Johansson5, B. Jonson5, O. Kirsebom2, H. Knudsen2, M.

Madurga1, A. Moro4, T. Nilsson5, G. Nyman5, K. Riisager2, O. Tengblad1, E. Tengborn5, D. Voulot3, F. Wenander3

ISOLDE – REX – MiniBall collaboration

1Institut Estructura de la Materia, CSIC, Spain2Institut for Fysik og Astronomi, Aarhus Universitet, Denmark

3ISOLDE, PH Department, CERN Switzerland4Departamento de FAMN, Universidad de Sevilla, Spain

5Fundamental fysik, Chalmers tekniska högskola, Sweden

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Thank you for your attention!