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Probing Light Neutron-Rich Systems

Probing Light Neutron-Rich Systems

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Probing Light Neutron-Rich Systems

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  1. Probing Light Neutron-Rich Systems Nigel Orr Group “Exotiques” LPC-Caen for the DEMON-CHARISSA Collaboration

  2. … toujours la même chose avec lui … mieux vaut peut-être rester ici avec mon ballon de rouge

  3. Probing Light Neutron-Rich Systems • Motivation • Breakdown in the N=8 shell closure - 12Be • Structure beyond the driplines • Spectroscopy of 13Be • N=4: 5H, 4n • Conclusions & Perspectives ...

  4. Structure of light, very neutron-rich systems ... 10Li 9He AZ = core+xn correlations/clustering 4n … driplines and beyond experimentally accessibleab initio calculations tractable, Shell Model in Continuum, ...

  5. N=8 shell closure - 12Be ? * 1.80 5/2+ [1p1/2]2 [2s1/2]2 [1d5/2]2 n-threshold p n 0.32 1/2--  0 1p3/2 1/2+ 11Be 1s1/2 psd-shell ordering in 12Be? *nb:first proposed by Fred Barker [J. Phys. G (1976) ] Figure courtesy Jeff Tostevin, UNiS

  6. core p0 core+1N Target High-Energy, Single-Nucleon Removal • s-1n ~ 10-100mb, rs ~ 100 mg/cm2 • forward focussing g ds/dp T+1N g  Excoreds/dp ns-1n(Jpcore) C2S REVIEW: Hansen, Tostevin, Ann. Rev. Nucl. Part. Sci. (2003)

  7. N=8 shell closure: C( 12Be,11Beg) @78MeV/nucleon* sexpt vs sGlauber  =0 C2S (ns1/2)  0.5 C2S (np1/2)  0.4 Eg=320 keV =1 C2S (nd5/2) = ?? n(p1/2)2,(s1/2)2,(d5/2)230%, 20%,50% * A. Navin et al., PRL (2000) G. Gori et al., PRC (2004)

  8. N=8 shell closure - 12Be n(d5/2)2 admixture 1.80 5/2+ [1p1/2]2 [2s1/2]2 [1d5/2]2 n-threshold p n 0.32 10Be+n 1/2--  0 1p3/2 1/2+ 11Be 1s1/2 psd-shell ordering in 12Be? Figure courtesy Jeff Tostevin, UNiS

  9. Single-Nucleon Removal to Unbound States/Nuclei:“Complete Kinematics” vn v0 v0 vcore T+1N Target pcore+n = pcore+ pnErel = m(vcore- vn)2/2qcore-n

  10. Experimental Setup “Complete Kinematics” Fragment CHARISSA 16 x Si-Si–CsI Identification (DE-E) Position (~1mm)  Energy (~1%) Neutrons DEMON 90 modules (NE213)  ToF & position  en ~ 10% enn ~ 1% + Cross-talk Rejection !!

  11. Resolution Efficiency Experimental Response Function *Complex geometry  simulations FWHM ~ 0.3 Ed 1/2 en enn * CHARISSA+DEMON @ ~30-40 MeV/nucleon

  12. Benchmark System - 7He Er=0.44, G0=0.16 MeV (g.s.)

  13. N=8 shell closure: C( 12Be,10Be+n) @41MeV/nucleon Counts 5/2+ 3/2- 5/2- Ex (11Be) MeV Ex (11Be) = Erel(10Be+n) + Sn LPC-CHARISSA-DEMON S. Pain, W.N. Catford, N.A. Orr et al.

  14. N=8 shell closure: C( 12Be,10Be+n) @41MeV/nucleon Counts s(5/2+) = 23±5 mb  C2S (nd5/2)  0.4 * 5/2+ 3/2- 5/2- Ex (11Be) MeV LPC-CHARISSA-DEMON S. Pain, W.N. Catford, N.A. Orr et al. * J.A. Tostevin : Preliminary

  15. Core-n correlations: modelling two-neutron halo systems

  16. Core-n correlations: modelling two-neutron halo systems 3-body systems  n-n and core-n interactions

  17. Core-n correlations: modelling two-neutron halo systems 3-body systems  n-n and core-n interactions 14Be  12Be-n interaction  spectroscopy of 13Be

  18. Vf Vf-Vn Vn 14B Target 13Be12Be+n Single-Proton Removal: C(14B,12Be+n) @ 41 MeV/nucleon • projectile neutron configuration preserved  Final states populated: ns1/2and nd5/2

  19. C(14B,12Be+n) @ 41 MeV/nucleon Ed (MeV) LPC Group “Exotiques” - JL Lecouey et al.

  20. C(14B,12Be+n) @ 41 MeV/nucleon s-wave resonance Er  0.7 MeV G0  2 MeV Ed (MeV) LPC Group “Exotiques” - JL Lecouey et al.

  21. C(14B,12Be+n) @ 41 MeV/nucleon s-wave resonance Er  0.7 MeV G0  2 MeV d-wave resonance Er = 2.5 MeV G0 = 0.4 MeV Ed (MeV) LPC Group “Exotiques” - JL Lecouey et al.

  22. Angular Correlations: C(14Be,12Be+n) @ 287 MeV/u * 14Be n1 13Be n2 12Be * H. Simon et al., priv. comm.

  23. 13Be: Experiment-Theory

  24. 13Be: Experiment-Theory 13Be : Ex ~ 2.5 MeV nd5/2

  25. 13Be: Experiment-Theory 13Be ground state: ns1/2 resonance (?)

  26. 13Be: Experiment-Theory 13Be : np1/2 Ex ??

  27. 5H : correlations beyond the dripline • most neutron-rich system known - N/Z=4 • extreme test of models • n-n correlations beyond the dripline • contradictory observations ...

  28. 5H : correlations beyond the dripline • most neutron-rich system known - N/Z=4 • extreme test of models • n-n correlations beyond the dripline • contradictory observations ... p(6He,pp) @ 36 MeV/uKorsheninnikov et al., PRL (2000) t(t,ptn) @ 19 MeV/uGolovkov et al., PLB (2004)

  29. Correlations beyond the dripline: 5H C(6He,t+n+n)X @ 30 MeV/nucleon Group Exotiques - G. Normand et al.

  30. Correlations beyond the dripline: 5H C(6He,t+n+n)X @ 30 MeV/nucleon Uncorrelated t+n+n/no FSI (“event mixing”) Group Exotiques - G. Normand et al.

  31. Correlations beyond the dripline: 5H C(6He,t+n+n)X @ 30 MeV/nucleon Er=1.8 ±0.2 MeV G0=2.1 ± 0.5 MeV Uncorrelated t+n+n/no FSI Group Exotiques - G. Normand et al.

  32. Single-proton Removal from 6He 5H 6He -1p p n 1p3/2 1p3/2 1s1/2 1s1/2 Jp=0+

  33. Single-proton Removal from 6He 5H 6He -1p p n 1p3/2 1p3/2 1s1/2 1s1/2 p1s1/2n(1p3/2)2 j=0+ Jp=0+ Jp=1/2+ [g.s.] p1s1/2n(1p3/2)2 j=2+ Jp=3/2,5/2+

  34. 5H: Comparison 3-body theory * Cross-talk eliminated 1/2+ 3/2+ 5/2+ 1/2+ (plane wave/ no FSI) Cross-talk included * 3-BODY MODEL: Shul ’gina et al.,PRC61(00)014312

  35. C(6He,t+n+n) @ 240 MeV/nucleon Meister et al., NUPA723(03)13 3-BODY MODEL: Shul ’gina et al., PRC61(00)014312

  36. Two-Neutron Intensity Interferometry:HBT Effect Correlation Function - Cnn FM Marqués et al., PLB (2000)

  37. 5H Decay: t+n+n Dalitz plot analysis * *Dalitz plots and 3-body correlations in breakup F.M. Marqués et al., PRC64(01)233 Group Exotiques G. Normand et al.

  38. 4H: C(6He,t+n)X @30 MeV/u Er 1.9 MeV G0 3.2 MeV t ~60 fm/c Group Exotiques - G. Normand et al.

  39. 5H: Cnn + Gaussian Source RMS rnn = 5.5 ± 1.7 fm deuteron rnp 3.8 fm Group Exotiques - G. Normand et al.

  40. “ … and what about the tetraneutron ?? ” * “ … and what about the tetraneutron ?? ” * • Clustering within nuclei •  can free An exist ? • Beyond 2n (Sn ~ -70keV) • 4n most likely • 4He(p-,p+ ), 7Li(11B,14O) … • New approach • Clustering within nuclei •  can free An exist ? • Beyond 2n (Sn ~ -70keV) • 4n most likely • 4He(p-,p+ ), 7Li(11B,14O) … • New approach *P. Regan (on numerous occassions after a few beers) *P. Regan (on numerous occassions after a few beers)

  41. Production: 14Be (35 MeV/u) + C 10Be + 4n Sn(14Be) = 5.2 MeV

  42. Detection à la Chadwick

  43. Detection à la Chadwick Detection via breakup

  44. Detection à la Chadwick Single-neutron response Detection via breakup FM Marqués et al., PRC (2002)

  45. Results: 14Be + C ABe + xn FM Marqués et al., PRC (2002)

  46. Results: 8He + C AHe + xn Group Exotiques: V. Bouchat et al. CHARISSA-DEMON

  47. Results: 8He + C AHe + xn PRELIMINARY Group Exotiques: V. Bouchat et al. CHARISSA-DEMON

  48. ... 4n as a (low-lying) resonance ? • Not considered in original • background/pileup estimates • Resonance does not live • long enough to reach • DEMON ... • Focusing of neutrons • from decay of 4n •  compatible with signal • but C2S, E, G… ??

  49. Conclusions • New reaction probe - high-energy nucleon removal - and analysis techniques to explore structure and correlations at and beyond the dripline • N=8 not a closed shell for 12Be (nor for 11Li) • N=9 ns1/2 - d5/2 inversion for 13Be (14B, 15C) … 14Be halo • 5H : broad Jp = 1/2+ g.s. (?? yi yf)

  50. Conclusions • New reaction probe - high-energy nucleon removal - and analysis techniques to explore structure and correlations at and beyond the dripline • N=8 not a closed shell for 12Be (nor for 11Li) • N=9 ns1/2 - d5/2 inversion for 13Be (14B, 15C) … 14Be halo • 5H : broad Jp = 1/2+ g.s. (?? yi yf)