1. Reaction experiments induced by light exotic nuclei at REX-ISOLDE
Olof TENGBLAD
Instituto de Estructura de la Materia
Consejo Superior de Investigaciones Científicas
Madrid Spain
Madrid-Aarhus-Göteborg

2. Probing the 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 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 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 Same configuration, beam energy and targets as October 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

3. Bound lithium isotopes
Stable
T1/2= 836 ms 178ms 8.5 ms
6Li
7Li
8Li
9Li
11Li – a halo nucleus
nuclear radius (fm)
Brief 11Li History
1966 found bound
1975 1st spectroscopy C. 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
mass number

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

5. Probing unbound 10Li @ REX
IS371
Elastic resonance scattering to investigate E, J of lowest T=2 states in 10Be analogues of gs and 1:st excited state of 10Li
IS371
T=2
T=1
9Li
d-polyethylen
IS367
Transfer 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
Post-accelerated 2.3 MeV/u 9Li beam from REX-ISOLDE on PE, d-PE, Be, target respectively.

6. IS371: elastic resonance scattering 9Li+1H
ungated
600 ms
BeamGate
EBIS gated T1
Time arrival of event [ms]
Excitation Energy in 10Be [MeV]
600< p< 1200
p < 600 ms
Rutherford Bkg
HIE ISOLDE with 5 MeV/u and ACTAR
would help to improve

7. IS367: Nucelon transfer reaction: 9Li+2H/9Be
Nuclear Physics A738(2004)
Nuclear Physics A748(2005)
Phys.Lett B635(2006)17-22
Phys.Lett B642(2006)
d(9Li,10Li*)p using REX-ISOLDE
9Li+n

8. Probing unbound 10Li @ REX
9Li (2x MeV/u
proton-ion
coincidences
8Li + t
9Li + d
10Li + p
9Li + d
Cut-off
[MeV]
11 6He
10 a
3.5 t
3.0 d
2.3 p
25 keV , s1/2 (?)
-1st 300 keV p1/2
-2nd 500 keV, p1/2
The 10Li structure play important role to understand the formation of the halo.
10Li at 25 keV above the 9Li+n; neutron on s-wave
1st excite at about 300 keV; neutron on p-wave (1+)
2nd excite state at about 500 keV on p-wave (2+)

9. IS446: Nucelon transfer reaction: 8Li+2H
ΔE-det. 32 x 32 strips 60 mm
2x2 mm2  < 3o resolution
Maximize angular coverage
Composition of the beam
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
Reaction cross-section on an absolute scale
Constant transmission → Monitor detector (observaction of C and oxigen as contaminant)
Rutherford scattered 8Li on 109Ag-target
Interpretation of the absolute differential cross section missing on progress coupling of several channels
dσ/dΩ (a.u.)
ΔE (MeV) a t p d
E (MeV)

10. Excitation-energies Excitation energy spectra Elastic  deuteron
Stripping
 triton
Eex(7Li)
Eex(8Li)
dσ/dE (a.u.)
dσ/dE (a.u.)
E (MeV)
E (MeV)
Pickup
 proton
Eex(9Li)
Excitation-energies
dσ/dE (a.u.)
E (MeV)

11. 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 potential
deformation length fm P
DWBA calculation
(Distorted Wave Born Aprox)
D potential between d & 8Li core
P potential p & 8Li + n
B Binding potential 8Li + picked up n D B

12. Elastic/inelastic: 2H(8Li,d)8Li*
Angular dependence of differential cross-section
Joint analysis of elastic and inelastic channels
Using DWBA and Coupled Channels CC methods
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
Couple Channels
DWBA
CC calculations show better agreement than DWBA, which confirms the importance of higher order effects

13. 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).

14. Stripping: 2H(8Li,t)7Li* Measured angular distribution 2H(8Li,t) 7Li*
cross section compared to;
DWBA dashed line
Coupled-Reaction-Channel CRC solid line
The CRC calculation reproduce the data well
Confirming the importance of multi-step process in this reaction.
The overall result demonstrate that the transfer reaction remains a useful tool for investigating nuclear structure.
Careful theoretical treatment is needed
And more examples to tune the parameters on.
The 8li + 2H reaction at REX-ISOLDE
E. Tengborn et.al. Accepted Phys Rev C (2011)

15. Transfer reactions with 11Be
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)
IS438 P192 Elastic scattering and fusion studies in the reactions 10,11Be+64Zn  A. Di Pietro et.al. Phys. Rev. Let. 105, , (2010)
IS430 P187 Study of neutron-rich Be isotopes with REX-ISOLDE
The same set-up was used
at one time

16. Transfer reactions with 11Be
Halo nucleus (also in bound excited state…)
Cluster structures in neighbours
N=8 broken in 12Be
12Be
states
T. Aumann et al, PRL 84 (2000) 35
MSU, neutron-knockout
R. Palit et al, PRC 68 (2003)
GSI, break-up
and others…
Knock relativistic energies: Be to 10Be

17. 11Be to 12Be What remains to do ?
R. Kanungo et al, PLB682 (10) 391
n-transfer at Triumf, 5 MeV/u
Neutron knockout establishing N=8 breaking, e.g. A. Navin
et al, PRL 85(00) 266; S.Pain et al, PRL 96 (06)
RIKEN exps, excited states on 12Be: H. Iwasaki et al, PLB
481 (00) 7, 491 (00) 8; S. Shimoura et al, PLB 560 (03) 31;
N. Imai et al, PLB 673 (09) 179
What remains to do ?
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
IS430 P187 Study of neutron-rich Be isotopes with REX-ISOLDE
Sept – 2nd beamline
Oct – T-REX (cut short, EBIS problems)
Sep – T-REX (very successful run !!)

18. 2005 run - results Beam of 11Be, deuterium target, 2nd beamline
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.
A. Moro, calculation: optical potential

19. T-REX and MINIBALL set-up
2010: Particle ID via DE-E
2010 improved experiment
T-REX and MINIBALL set-up a t d p
p d t
T-REX detectors are too thick:
150 mm stops 16 MeV a  no DE-E
2005 data

20. Stripping: 11Be(d,t)10Be* 2+, 1-, 0+, 2- 2+ 0+ 2+ to 2+ 2- to 2+

21. 10Be+t coincidences i.e. complete kinematics
θx versus θy

22. Elastic/Inelastic: 11Be(d,d)11Be*
320 keV

23. Pickup: 11Be(d,p)12Be* Excitation spectra
Black: Total
Brown: Bg from reactions on C
Red: 2+1
Green: 0+2
Blue: 1-1 .
Gamma lines in coincidence with p.
Purpel:
The four above combined
511 line:
0+2 pair production
Doppler corrected
2100: : 1-1

24. Gamma-gated 12Be spectra

25. Cross sections from (d,p)
Preliminary: Coupled channel calculations
0+1 gs
11Be(d,p)12Be
2+1
1-1

26. 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

27. 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, Spain
2Institut for Fysik og Astronomi, Aarhus Universitet, Denmark
3ISOLDE, PH Department, CERN Switzerland
4Departamento de FAMN, Universidad de Sevilla, Spain
5Fundamental fysik, Chalmers tekniska högskola, Sweden

28. Thank you for your attention!