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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 Characteristic Nuclear structure near neutron-drip line?
b-Stable n p continuum -1MeV<Sn<0MeV Beyond n p continuum Sn<1MeV 1n separation energy Sn=8MeV More n-rich p n 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? 3

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

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 Deformation? K Ar Halo? Cl S Drip Line? Continuum? Si P Al N=28 Mg N=20 Na Ne N=16 F O 37Mg N C 31Ne B 25O 26O Be 28O 21C 1n halo known Li He 22C 2n halo known N=8 H 18B 19B 4n halo/skin 5

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, (2014).) 31Ne 31Ne* 30Ne 30Ne n (g) 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 7

8 31Ne New 1n Halo Systems 31Ne and 37Mg:
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, , 2014

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

10 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 dB(E1) dEx = 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) 10

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 BigRIPS 2014 SHARAQ ----- 会議メモ (12/10/14 18:31) ----- This is the RIKEN RI Beam Factory, RIBF, in The accelerators and the fragment Separator BigRIPS has completed in 2007, and this is the first of the new generation RI beam facility. It contains a series of the Cyclotorons, and the last cyclotron SRC, super conducting cyclotron is the world largest cyclotron… 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:~500pnA 2014 238U: ~ 30 pnA 2015

13 Superconducting Analyzer for MUlti-particle from RAdio Isotope Beam
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 deg(V) (~50% coverage < Erel ~ 5MeV) Moderate Erel Resolution DE = 200 keV (s) at Erel=1MeV Stage: Rotatable ( degrees) Variety of Physics Opportunities Superconducting Magnet (3T, 2m dia. Pole 80cm gap) RI beam from BigRIPS Target rotatable Neutron(s) Proton Heavy Ion

14 SAMURAI Superconducting 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 25O 26O 28O Be 21C Li He 22C N=8 H 18B 19B

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, (2010). sR(mb) S2n= -0.14(46) MeV L.Gaudefroy et al. PRL109,202503(2012). N=16 Magicity? 20 1d3/2 A 16 2S1/2 1d5/2 A.Ozawa et al., PRL 84, 5493 (2000). 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

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

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

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

20 Study of unbound nuclei 25O and 26O at SAMURAI
Spokesperson Yosuke Kondo Experimental study of unbound oxygen isotopes towards the possible double magic nucleus 28O T. Otsuka et al., PRL105, (2010). Drip line 3N force: significant at N>16 24Ne 25Ne 26Ne 27Ne 28Ne 29Ne 30Ne 31Ne 32Ne 23F 24F 25F 26F 27F 28F 29F 30F 31F 22O 23O 24O 25O 26O 27O 28O Z=8 21N 22N 23N N=20 Again, this is the nuclear chart. One of the important problem of nuclear physics is the location of the drip line, which is strongly affected by the nuclear structure. The neutron drip line regularly evolves with increase of proton number like this dashed line. But anomalous behavior can be seen at Z=8. This anomalous behavior may be due to the shell evolution. So, it is very interesting to investigate towards 28O, which has Z=8 and N=20. G. Hagen et al., PRL108, (2012). H. Hergert et al., PRL110, (2013). S.K.Bogner et al., PRL113, (2014). 20C 21C 22C Oxygen Anomaly 19B N=16? 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 2n radioactivity of 26O? x 25O+n 26O 24O+2n ~770keV ?
E. Lunderberg et al. PRL108, (2012) Er < 200keV 26O: 24O(0+) ⊗ (nd3/2)2 26O 24O+2n L.V. Grigorenko et al. PRC 84, (2011) Theory Usual 1n decay G~MeV or keV C. Caesar et al.PRC88, (2013) Excite state at 4.2MeV? Er < 120keV (95% CL) t < 5.7ns T1/2= ps (3ps systematic error) 2n radioactivity? Z. Kohley et al,PRL110, (2013) 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?

22 Experimental Setup at SAMURAI at 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
24O+n Edecay Edecay=750keV 25Ogs 26F+C 25O*24O+n Kondo et al. Edecay=749(10) keV = 88(6) keV C.R.Hoffman et al.,(MSU) PRL100, (2008) Previous Works (GSI) C.Caesar, PRC 2013 (MSU) Hoffman, PRL 2008

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

25 Barely unbound nucleus 26O
Present Results on 25O and 26O 1.27(11) MeV 18(5) keV 749(10) keV (2+) 25O+n 0+ 24O+n+n 25O+n 26O N=16 shell closure is confirmed USDB fail to describe E(2+) of 26O Effect of pf shell? E Centrifugal Barrier Extremely weakly UNBOUND state! 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-line 31Ne 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
Counts A 23O 22O 24O 27F+CAO @SAMURAI ~13s separation! 21O @GSI 22O C. Caesar et al. PRC(2013). 23O 24O Clear Particle identification!  High resolving power of the SAMURAI spectrometer A/DA=310 (1s)

30 Eg=1.6MeV gated

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