20 November 2003Nens 031 Threshold and Continuum Structures in Exotic Nuclei Ian Thompson University of Surrey, Guildford, England with J. Tostevin, J. Mortimer, T. Tarutina (Surrey), B. Danilin (Surrey, Kurchatov)

20 November 2003Nens 032 Topics to Discuss zFew-body vs many-body behaviour zNeed for spectroscopy from breakup yKnockout to bound states y1N stripping of Borromean halo nuclei zElastic breakup: yE1 and E2 in 8 B breakup? yContinuum states: energy correlations zConclusions

20 November 2003Nens 033 Few- vs many-body dynamics zNuclei typically show few-body behaviour just near and above the cluster separation thresholds. zMany exotic nuclei have just one or a few bound states, and hence show pronounced cluster dynamics even in their ground states.

20 November 2003Nens 034 Role of the Continuum? zThe continuum appears in several ways: yPart of expansion of bound states; xeg needed in RPA for weakly bound states yDominated by resonances; xThese ‘unbound states’ identified eg with shell model eigenstates above threshold yIn non-resonant continuum; xeg in breakup reactions. zALL important parts of nuclear structure!!

20 November 2003Nens 035 Reactions to probe structure zStructure may be probed by elastic scattering or cluster transfers, zbut breakup is typically the largest. zReview: ythe structure information that is present in breakup amplitudes, ybound structure details that can be extracted from different classes of breakup reactions.

20 November 2003Nens 036 Stripping Reactions zStripping = inelastic breakup, removes a surface nucleon by a high-energy interaction with a target. yCan reveal the spectroscopic factors for a wide range of final states. yThese states may be distinguished by coincident  -rays. zReview the measurement of spin, parity, and absolute spectroscopic factors.

20 November 2003Nens 037 Contributions from surface and beyond 12 Be+ 9 Be  11 Be(gs)+X, 80A MeV Eikonal reaction theory for the breakup 9 Be c 12 Be b v

20 November 2003Nens F 16 O 14 N 12 C 11 B N=8 N=14 Momentum content: p-shell E.Sauvan et al., Phys Lett B 491 (2000) 1 distributions narrow (weak binding) or s-states as one crosses shell or sub-shell closures No gamma detection

20 November 2003Nens 039 SM calculation predict no 16 C(0 + ) in the 17 C(g.s.). Experiment measured a 20% branch into 16 C(0 + ). Higher order processes? 9 Be( 17 C, 16 C  )X (E beam =60 MeV/A) Maddalena et al., PRC63(01) Knockout reactions (a) 8% s + 92% d (b) 26% s + 74% d (c) 100% d

20 November 2003Nens 0310 N=8 neutron shell closure in 12 Be? C 2 S=0.42 C 2 S=0.37 =0 =1 from A. Navin et al., PRL 85 (2000) 266

20 November 2003Nens 0311 Ground state structure of 8 B from D.Cortina-Gil et al., Phys Lett B 529 (2002) 36, NPA 720 (2003) 3 Proton removal from 8 B measured at the GSI with gamma coincidences, sees a (15%) branch from an excited 7 Be(1/2 - ) core component in the 8 B wave function. p 3/2 137 keV p 3/2 566 keV

20 November 2003Nens 0312 Deduced vs. shell model spectroscopic factors P.G. Hansen and J.A.Tostevin, ARNPS 53 (2003), 219 More bound systemsCan define reduction factor th  Shell model structure plus eikonal reaction Mostly weakly bound n-rich systems

20 November 2003Nens 0313 Knockout: Absolute spectroscopy 0.53(2) 0.49(2) (e,e'p) 0.51(3) 0.67(5) 0.68(4) 0.56(3) From B.A. Brown et al. PRC 65 (2002) (R) S p =15.96 S n = S p = S n = 15.66

20 November 2003Nens 0314 Strongly bound hole states neutron proton P.G. Hansen and J.A.Tostevin, ARNPS 53 (2003), 219 inclusive Reduction Factor R s

20 November 2003Nens 0315 Weakly bound states neutron proton P.G. Hansen and J.A.Tostevin, ARNPS 53 (2003), 219 Reduction Factor R s Expts with good statistics

20 November 2003Nens 0316 Combining Knockout and other Tools 9 Be( 19 C, 18 C  )X (E beam =60 MeV/A) d-wave s-wave S n =0.8(0.3) MeV Maddalena et al., PRC (2001)

20 November 2003Nens Neutron stripping from three-body Borromean Nuclei zRemoval of a neutron from 6 He, 11 Li, 14 Be, ypopulates states of 5 He, 10 Li or 13 Be. yExperiments measure decay spectrum of 5 He = 4 He + n, 13 Be = 12 Be + n, etc zCan we predict any energy and angular correlations by Glauber model? zCan we relate these correlations to the structure of the A+1 or the A+2 nucleus?

20 November 2003Nens N stripping from 6 He g.s.  Calculate overlaps: for a range of 5 He( E α-n )> bin states, zsmooth histogram of Glauber bin cross sections. zGSI data (H.Simon) Theory: σ str =137 mb, σ diff =38 mb Expt: σ str =127±14 mb, σ diff =30±5 mb from T. Tarutina thesis (Surrey) Promising technique!

20 November 2003Nens N stripping from 14 Be g.s.  Calculate overlaps: zInert-core 13,14 Be wfs. zGSI data (H.Simon) yfrom T. Tarutina thesis (Surrey) Theory: σ str =109 mb, σ diff =109 mb Expt: σ str =125±19 mb, σ diff =55±19 mb  See softer data, and not pronounced virtual- s and resonant- d peaks.

20 November 2003Nens 0320 Elastic Breakup zElastic Breakup = Diffraction Dissociation: yall nuclear fragments survive along with the target in its ground state, yprobes continuum excited states of nucleus. yFor dripline nuclei, with few discrete states, these breakup reactions are the main probe of excited states zReview correlations in the three-body continuum of Borromean nuclei.

20 November 2003Nens 0321 E1 & E2 breakup of 8 B zOne-proton bound state known: y 7 Be  (0p 3/2 +0p 1/2 )| 2+ at MeV zNeed spectroscopy of non-resonant continuuum! yB(E1) & B(E2) for transition p  s,d need to be accurately known yE1 and E2 amplitudes interfere in p || ( 7 Be) momentum distribution yso measure relative E2/E1 amplitudes from asymmetries.

20 November 2003Nens B Pb  7 Be parallel momentum distributions Dot-dashed: semiclassical Coul. Solid: Coulomb+nuclear DWBA Dashed: CDCC coupled channels - reduced asymmetry 44 MeV/A CDCC calculations with scaled E2 amplitudes - need to increase asymmetry again! from Mortimer et al., Phys Rev C 65 (2002) 64619

20 November 2003Nens body Borromean Nuclei zGround state plot: z Continuum 3-3 scattering states  Now average scattering wave functions over angles of k nn and k cn-n z Obtain similar plots for continuum energies.

20 November 2003Nens 0324 Virtual states & Resonances Virtual n-n pole Effect of n-n ‘resonance’ in E(c-n), E(cn-n) coordinates from B. Danilin, I. Thompson, et al (in preparation)

20 November 2003Nens He excitations & resonances Pronounced 2 + resonance No pronounced 1 - resonance

20 November 2003Nens 0326 Assorted Structure Challenges zLight nuclear structure: y 6 Li quadrupole moment? y 8 B E2 transitions ? yIntruder states in 11 Be, 11 Li, 12 Be etc ? xCan these be found in a model beginning with a NN force? xAre tensor and/or 3-body forces required? xCore excitation in (near-) halo nuclei? yThresholds: are these fitted simultaneously?

20 November 2003Nens 0327 Conclusions zNear-threshold states give rise to cluster dynamics and breakup zContinuum states necessary for spectroscopic probes. zSpectroscopy of states in the continuum is just as important as spectroscopy of discrete states (bound states or discrete resonances).