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Weakly bound and unbound nuclei

Weakly bound and unbound nuclei. Takashi Nakamura Department of Physics, Tokyo Institute of Technology. The 9 th Japan-China Joint Nuclear Physics Symposium (JCNP2015), 7-12/Nov/2015, Osaka Univ. Contents. Introduction: Drip Lines and Barely bound/unbound nuclei

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Weakly bound and unbound nuclei

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  1. Weakly bound and unbound nuclei Takashi Nakamura Department of Physics, Tokyo Institute of Technology The 9th Japan-China Joint Nuclear Physics Symposium (JCNP2015), 7-12/Nov/2015, Osaka Univ.

  2. Contents • Introduction: • Drip Lines and Barely bound/unbound nuclei • Probes: Coulomb and Nuclear Breakup • at intermediate energies • SAMURAI Facility at RIBF at RIKEN • Coulomb/Nuclear Breakup of Borromean 2n-Halo 22C • Spectroscopy of 25O,26O -- @ SAMURAI at RIBF • Summary and Outlook

  3. continuum continuum Characteristic Nuclear structure near neutron-drip line? Neutron Drip-line b-Stable Beyond Sn<1MeV -1MeV<Sn<0MeV 1n separation energy Sn=8MeV More n-rich n p n p n p • Neutron Drip Line • Fermi levels between n and p—Very Different • Valence neutron – Loosely-Bound/Unbound • Neutron Halo/Skin (Neutron-matter surface) • Continuum • Strong cluster-like correlation • dineutron?

  4. Dineutron? A.B.Migdal Strongly correlated “dineutron” on the surface of a nucleus Sov.J.Nucl.Phys.238(1973). n n Dineutron: @ Low-dense neutron skin/halo? /surface of neutron star? n n Unbound a= -18 fm S=1 M.Matsuo PRC73,044309(2006). A.Gezerlis, J.Carlson, PRC81,025803(2010) Electric-Dipole (E1) Response of 11Li 11Li q12 n Dineutron Correlation Strongly Polarized  Strong E1 Excitation core n n-star Indirect Hint of Dineutron Correlation T.N. et al. PRL96,252502(2006).

  5. Evolution Towards the Stability Limit Where is the neutron drip line? What are characteristic features of drip-line nuclei? How does nuclear structure evolve towards the drip line? Shell? Ca K Deformation? Ar Halo? Cl S Drip Line? Continuum? P Si Al N=28 Mg N=20 Na Ne N=16 F O 37Mg N C 31Ne B 26O 25O 28O Be 21C 1n halo known Li 22C 2n halo known He N=8 19B 18B H 4n halo/skin

  6. Probes– Nuclear and Coulomb breakup of drip-line nuclei at intermediate energies

  7. Probe-1: Nuclear Breakup – Case of 1n Halo e.g. 1n knockout reaction of 31Ne(TN et al. , PRL112,142501 (2014).) 31Ne 31Ne* 30Ne 30Ne (g) n 240MeV/u C Target p f g ray in coincidence  30Ne(2+) / 30Ne(0+) Contribution s-1n and P// distribution  of valence n, configuration Theory: Eikonal Approximation

  8. New 1n Halo Systems 31Ne and 37Mg: 31Ne 30Ne core p-wave halo neutron Deformation b~0.5 (~ 3:2) Strongly deformed although it is N=21 (close to 20) 37Mg: N.Kobayashi, TN et al., PRL 112, 242501, 2014

  9. Probe-1Nuclear Breakup – Case of 2n Halo e.g. 22C 2+ (?) ds/dErel 22C* 20C 22C n n 12C 12C Inelastic scattering P//(20C) 12C 21C* ds/dErel s 20C 22C n d Knockout reaction N.Kobayashi,TN,PRC2012

  10. dB(E1) dEx Probe-2: Coulomb Breakup Photon absorption of a fast projectile Invariant Mass 22C 22C* 20C n g(virtual photon) b>0.3 n High-Z Target (Pb) Di-neutron Correlation Single particle state (Halo) Equivalent Photon Method dsCB 16p3 = NE1(Ex) dEx 9hc Cross section = (Photon Number)x(Transition Probability) C.A. Bertulani, G. Baur, Phys. Rep. 163,299(1988). Halo  Soft E1 Excitation (E1 Concentration at Ex<1MeV)

  11. SAMURAI Facility at RIBF at RIKEN

  12. RIKEN RI Beam Factory (RIBF) Completed in 2007 New-Generation RI-beam facility SCRIT 2013 SLOWRI 2014 SAMURAI ZDS 2012 2008 SRC Rare RI RING 2014 BigRIPS SHARAQ 2007 2009 SRC: World Largest Cyclotron (K=2500 MeV) Heavy Ion Beams up to 238U at 345MeV/u (Light Ions up to 440MeV/u) eg. 48Ca beam (345 MeV/nucleon) ~200pnA (250pnA max.) 238U beam (345 MeV/nucleon) ~12pnA (15pnA max.) Increasing Year by Year! 48Ca:~500pnA2014 238U: ~ 30 pnA 2015

  13. SAMURAI Superconducting Analyzer for MUlti-particle from RAdio Isotope Beam Kinematically Complete measurements by detecting multiple particles in coincidence Large momentum acceptance Brmax / Brmin ~ 2 – 3 Good Momentum Resolution Dp/p~ 1/1500 Large Bending Angle (~60deg) +4 Tracking Detectors T.Kobayashi NIMB317, 294 (2013) Large angular acceptance for n +-8.8 deg (H) x +-4.4 deg(V) (~50% coverage < Erel ~ 5MeV) Moderate Erel Resolution DE = 200 keV (s) at Erel=1MeV Stage: Rotatable (-5 -- 95 degrees) Variety of Physics Opportunities Superconducting Magnet (3T, 2m dia. Pole 80cm gap) RI beam from BigRIPS Target Neutron(s) rotatable Proton Heavy Ion

  14. SAMURAISuperconducting Analyzer for MUlti-particle from RAdio Isotope Beam March 2012

  15. Breakup Experiments at SAMURAI -- Results from Day-One campaign experiments at SAMURAI Coulomb Breakup of 19B and 22C, Nakamura et al. Study of 18B,21C, and excited states of 19B,22C, Orr et al. Structure of Unbound Oxygen Isotopes 25O,26O, Kondo et al. F O N C B 28O 26O 25O Be 21C Li 22C He N=8 19B 18B H

  16. 22C (Z=6,N=16) • Prominent 2n-Halo? • Reaction cross section measurements • (<rm2>)1/2=5.4(9) fm c.f. ~3.5 fm11Li • K.Tanaka et al., PRL 104, 062701(2010). 22C sR(mb) S2n= -0.14(46) MeV Z=8 L.Gaudefroy et al. PRL109,202503(2012). 20C • N=16 Magicity? 19C A 1d3/2 2S1/2 A.Ozawa et al., PRL 84, 5493 (2000). 1d5/2 • Heaviest s-wave dominant 2n Halo within reach? c.f. 3s1/2 Halo: Far away for the current and near-future RIB facilities N~60-70 16 20

  17. SAMURAI Experiment May/2012 First Full Exclusive Coulomb/Nuclear Breakup Measurement of 22C and 19B ~10cps RIBF (~10cph RIPS) 22C+CAZ+X Pb3.26g/cm2 C 1.79g/cm2 n 7 23N 19C 20C 22N 22C n 22C 6 DE 20C Z 19B 5 17B 19C 19B 17B 4 20C 14Be 3 22C 240MeV/nucleon 2.8 3 3.2 3.4 3.6 3.8 4 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4 A/Z A/Z

  18. Heavy Ion + 1 neutron : 22C(22N)+C21C*20C+n Spokesperson: N.A.Orr, J.Gibelin 29F 31F 27F 26F 22F 23F 24F 25F 30F 28F 21O 22O 23O 24O 22N21C*20C+n 22N 20N 21N 23N S.Leblond Preliminary 22C 19C 20C 21C N=16 19B 22N21C*20C+n 18B S.Mosby et al.(MSU) NPA909,69(2013). s 22C21C*20C+n Preliminary 1d3/2 2S1/2 1d5/2 Erel(MeV) d s 1p1/2 1p3/2 0 1 2 3 Edecay(MeV) 1s1/2 5 2 0 1 3 4 Spectra from S.Leblond/N.A. Orr 2 16 20 2 8 22C Edecay(MeV)

  19. Coulomb Breakup of 22C (20C+n+n Spectrum) Spokesperson: T.Nakamura 22C+Pb22C* 20C+n+N Very Preliminary ! R.Minakata (Tokyo Tech) 0 1 2 3 4 5 6 7 8 9 10 counts Erel(MeV)

  20. Study of unbound nuclei 25O and 26O at SAMURAI Spokesperson Yosuke Kondo T. Otsuka et al., PRL105, 032501 (2010). Experimental study of unbound oxygen isotopes towards the possible double magic nucleus 28O Drip line Drip line 28Ne 29Ne 31Ne 26Ne 32Ne 25Ne 27Ne 30Ne 24Ne 3N force: significant at N>16 29F 31F 26F 27F 23F 24F 25F 30F 28F 22O 23O 24O 25O 26O 27O 28O Z=8 22N 21N 23N N=20 G. Hagen et al., PRL108, 242501(2012). H. Hergert et al., PRL110, 242501(2013). S.K.Bogner et al., PRL113, 142501(2014). 22C 20C 21C Oxygen Anomaly N=16? 19B Continuum Effect: A.Volya, V.Zelevinski, PRL94,052501(2005). nn correlations: L.V. Grigorenko et al., PRL111,042501(2013). K. Hagino, H. Sagawa PRC89,014331(2014).

  21. ~770keV ? 2n radioactivity of 26O? 25O+n x E. Lunderberg et al. PRL108, 142503 (2012) L.V. Grigorenko et al. PRC 84, 021303 (2011) 26O: 24O(0+) ⊗ (nd3/2)2 26O 24O+2n Large uncertainty of experimental study • Only upper limit is given for the ground state energy • Large systematic error in the lifetime measurement • Excited State of 26O? Theory Z. Kohley et al,PRL110,152501 (2013) T1/2=4.5+1.1-1.5ps (3ps systematic error) 2n radioactivity? Er < 200keV C. Caesar et al.PRC88, 034313 (2013) Usual 1n decay G~MeVor keV Er < 120keV (95% CL) t < 5.7ns Excite state at 4.2MeV?

  22. Experimental Setup at SAMURAIat RIBF C target (1.8g/cm2) MWDC Ionization Chamber Superconducting Dipole Magnet (B=3.0T) NEBULA n 2 MWDCs 2Plastics n 27F ~210MeV/u (from BigRIPS) DALI2 MWDC 24O Hodoscope

  23. Decay energy spectrum of 25O Edecay 26F+C 25O*24O+n Edecay=750keV 25Ogs Kondo et al. • Edecay=749(10) keV • = 88(6) keV 24O+n C.R.Hoffman et al.,(MSU) PRL100, 152502 (2008) (GSI) C.Caesar, PRC 2013 Previous Works (MSU) Hoffman, PRL 2008

  24. Decay energy spectrum of 26O (24O+2n, 24O+n) 26Ogs 26Ogs 27F+C26O,25O 24O+n+X 27F+C26O24O+2n No peak at ~4.2MeV 26O1st New! 26O1st+25Ogs Counts /20keV Counts /50keV Edecay(24O+n) Edecay(24O+n+n) =Edecay(24O+n)+Edecay(25O+n) Edecay(24O+n+n) Finite Value! n 24O • Most likely 2+ n

  25. Barely unbound nucleus26O Present Results on 25O and 26O (2+) 1.27(11) MeV 749(10) keV 25O+n 0+ 18(5) keV 24O+n+n 25O+n 26O Centrifugal Barrier • N=16 shell closure is confirmed • USDB fail to describe E(2+) of 26O • Effect of pf shell? Extremely weakly UNBOUND state! E • 3N-forces, pf shell, continuum Submitted to PRL Next step: Study of 27O and 28O in Nov.-Dec

  26. Summary and Outlook Coulomb and Nuclear Breakup Useful tool to probe weakly-bound states (HALO) near/beyond the drip-line31Ne TN, N.Kobayashi, PRL2014, 37Mg N.Kobayashi, TN, PRL2014. SAMURAI Facility at RIBF (since 2012) Powerful equipment for various experiments using RI beams Coulomb/Nuclear Breakup of 22C at SAMURAI S.Leblond, J.Gebelin, M.Marques, N.Orr, R.Minakata, S.Ogoshi,TN, et al. 21C spectrum  pin down s and d 1hole state of 22C Large Coulomb breakup cross sections Spectroscopy of 25O,26O at SAMURAI • Y.Kondo, J.Tsubota, TN et al. • 26O(0+gs): Very weakly unbound 2n states  Correlation? Continuum? • 26O(2+): Found for the first time at Erel=1.28(11) MeV  Shell Evolution? • Keys to understand Oxygen drip-line anomaly, Shell Evolution Near Future: Variety of unbound states along n-drip line  28O (Possible unbound doubly magic nucleus, 24O+4n)

  27. Day-one Collaboration Tokyo Institute of Technology: Y.Kondo, T.Nakamura, N.Kobayashi, R.Tanaka, R.Minakata, S.Ogoshi, S.Nishi, D.Kanno, T.Nakashima, J. Tsubota, A. Saito LPC CAEN: N.A.Orr, J.Gibelin, F.Delaunay, F.M.Marques, N.L.Achouri, S.Leblond, Q. Deshayes Tohoku University : T.Koabayshi, K.Takahashi, K.Muto RIKEN: K.Yoneda, T.Motobayashi ,H.Otsu, T.Isobe, H.Baba,H.Sato, Y.Shimizu, J.Lee, P.Doornenbal, S.Takeuchi, N.Inabe, N.Fukuda, D.Kameda, H.Suzuki, H.Takeda, T.Kubo Seoul National University: Y.Satou, S.Kim, J.W.Hwang Kyoto University : T.Murakami, N.Nakatsuka GSI :Y.Togano Univ. of York: A.G.Tuff GANIL: A.Navin Technische Universit¨at Darmstadt: T.Aumann Rikkyo Univeristy: D.Murai Universit´e Paris-Sud, IN2P3-CNRS: M.Vandebrouck

  28. Backup

  29. Mass identification@SAMURAI 27F+CAO @SAMURAI 22O Clear Particle identification!  High resolving power of the SAMURAI spectrometer @GSI 22O Counts C. Caesar et al. PRC(2013). ~13s separation! 23O 24O 21O 23O 24O A A/DA=310 (1s)

  30. Eg=1.6MeV gated

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