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

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

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. 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 mass number

Neutron-rich lithium isotopes X 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.

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.

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

IS367: Nucelon transfer reaction: 9Li+2H/9Be Nuclear Physics A738(2004)511-514 Nuclear Physics A748(2005)374-392 Phys.Lett B635(2006)17-22 Phys.Lett B642(2006)449-454 d(9Li,10Li*)p using REX-ISOLDE 9Li+n

Probing unbound 10Li @ REX 9Li (2x105 pps) @ 2.77 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 -gs @ 25 keV , s1/2 (?) -1st excited @ 300 keV p1/2 -2nd state @ 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+)

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)

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)

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 1.728 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

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

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).

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)

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, 022701, (2010) IS430 P187 Study of neutron-rich Be isotopes with REX-ISOLDE The same set-up was used at one time

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) 034318 GSI, break-up and others… Knock out @ relativistic energies: 11Be to 10Be

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) 032502 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. 2005 – 2nd beamline Oct. 2009 – T-REX (cut short, EBIS problems) Sep. 2010 – T-REX (very successful run !!)

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

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

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

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

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

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: 2+1 2700: 1-1

Gamma-gated 12Be spectra

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

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

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

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