Hiroshi Watanabe. Shapes and Symmetries in Nuclei: from Experiment to Theory (SSNET), November 7-11, 2016, CSNSM, Orsay, France

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1 Hiroshi Watanabe Shapes and Symmetries in Nuclei: from Experiment to Theory (SSNET), November 7-11, 2016, CSNSM, Orsay, France

2 Radioactive Isotope-Beam Factory (RIBF) at RIKEN RILACⅡ RILAC Sakurai s talk on Wednesday AVF frc RRC SRC History of max. beam intensities 1 pμa (Goal) IRC BigRIPS 4000 species to be produced (More than 1000 new isotopes)

3 The EURICA (EUROBALL-RIKEN Cluster Array) project In collaboration with - Gammapool for 12 Cluster detectors - RISING/PreSPEC for support structure and electronics

4 EURICA at RIBF in Approved BT with Grade A or higher: ~100 days 100 Sn and its vicinity Shape transitions near mid 2 -shell Isomers below 100 Sn Two-proton decay T z =-2 β decay K-isomers, octupole correlation Structual evolution beyond 132 Sn Seniority isomers in 136,138 Sn Shapes and isomers below 132 Sn T 1/2, Q β, P n in the vicinity of 128 Pd Exotic shapes near 110 Zr Single-neutron states in 79,81 Zn and 77 Ni r-process interest around 78 Ni Deformation in 70,72 Fe

5 7-element Cluster-type HPGe detectors 12 with Add-back ~10 1 MeV w/o Add-back WAS3ABi: Wide-range Active Silicon-Strip Stopper Array for Beta and ion detection DSSSD strips 1-mm pitch 8 layers (2012) 5 layers (2013)

6 Fast timing demonstration with EURICA 18 LaBr 3 (Ce) scintillators (Φ1.5 2 ) on three vacant slots for γ rays Contributed from U. of Surrey and Brighton BC-418 plastic counters (2-mm thick) beside the DSSDs for β rays Fast-timing measurement LaBr 3 (Ce) γ DSSD RI β Plastic

7 Decay spectroscopy of 172 Dy

8 EURICA experimental campaign at RIBF in November, 2014

9 Dy Middle of the major shells between 132 Sn and 208 Pb HFB calculations with D1S Gogny Maximum ground-state deformation? Nuclear Physics Where does the largest deformation occur? How the neutron excess affect shapes, pairing? Sub-shell closures stabilize the shape? Nuclear Astrophysics REE peak (A 165) Formation of the rare-earth element (REE) peak in the r-process

10 Intrinsic excitations in deformed nuclei : Collective vibrations Single-particle orbitals near the Fermi surface Intrinsic excitations K π = 2 + γ vibration ( N = 0 or ±2, n z = 0, Λ = K = ±2) Instantaneous breaking of axial symmetry Soft mode of γ instability or rigid triaxial deformation K π = 0 + β vibration, pairing excitation, intruder states, shape coexistence... Axial symmetry preserved K π = 0 -, 1 -, 2 -, 3 - Octupole vibration ( j = l = 3) vibrational well-deformed Good testing ground for collective model calculations

11 Intrinsic excitations in deformed nuclei : K isomer Phil Walker s talk on Monday R I K Change direction = Ω j j λ λ I i I f Ki K f λ I i, Ki,τ γ I f, K f Spin selection Yes K-selection Sort of! K hindered transitions Weisskopf hindrance Reduced hindrance The degree of K forbiddenness F f ν = τ = exp γ / F 1/ ν τ W ν = K λ Identification and characterization of K-isomers provides information on Single-particle orbits near the Fermi surface Pairing and other residual interactions Axial (a)symmetry (γ degree of freedom)

12 K π = 8 - isomers in N = 106 G.D. Dracoulis, Phys. Scr. T152, (2013) Neutron pairing strength ν7/2 - [514]ν9/2 + [624] Studied by deepinelastic reactions 5.8 s 172 Dy

13 In-flight fission of 238 U + Isotope separation Nov (3 days) 169 Dy 170 Dy 171 Dy 167 Tb 166 Gd 164 Tb 165 Tb 168 Tb 169 Tb 170 Tb 167 Gd 168 Gd 165 Eu 166 Eu 167 Eu Q = Z H-like High intensity (10~15 pna) Slits optimized for 170,172 Dy ΔA/Q ~ 0.05 % Separate charge state Ion BigRIPS On DSSD 170 Dy Gd 163 Gd 170 Dy setting 168 Dy 170 Ho 171 Dy 176 Er 164 Gd 161 Eu 162 Eu 171 Ho 172 Dy 163 Eu 160 Sm 161 Sm 170 Dy 176 Er 173 Ho 174 Ho 175 Ho 174 Ho 173 Dy 164 Sm 165 Sm 159 Pm 160 Pm 172 Dy Dy 168 Dy 166 Tb 169 Dy 171 Tb 172 Tb 169 Gd 170 Gd Heaviest isotope spectroscopic study done so far at RIBF 166 Tb 167 Tb 167 Tb 170 Tb 168 Tb 165 Gd 166 Gd 165 Gd 166 Gd Isomer in μs Isomer in ms 164 Eu 163 Eu 164 Eu 165 Eu 172 Dy setting

14 172 Dy H. Watanabe et al., PLB 760 (2016) 641 No level information before 11 new γ rays observed by gating on low-energy electrons Coincidence with internalconversion (IC) electrons Decay from a long-lived isomer Observation of the Dy K α -X ray at 45.8 kev 76-keV γ ray disappears for E e 80 kev 0 < E e 230 kev 0 T e < 4 s 0 < E e 80 kev 0 T e < 4 s γ gate: 290 kev γ gate: 400 kev γ gate: 713 kev Electron with γ gates

15 172 Dy H. Watanabe et al., PLB 760 (2016) 641 No level information before 11 new γ rays observed by gating on low-energy electrons Coincidence with internalconversion (IC) electrons Decay from a long-lived isomer Observation of the Dy K α -X ray at 45.8 kev 76-keV γ ray disappears for E e 80 kev 0 < E e 230 kev 0 T e < 4 s 0 < E e 80 kev 0 T e < 4 s γ gate: 290 kev γ gate: 400 kev γ gate: 713 kev Electron with γ gates Level scheme constructed based on γ-γ coincidence, energy matching, feeding patterns, and systematics K π = 8 - isomer (T 1/2 = 0.75 s) at 1278 kev Ground-state (g.s.) rotational band γ-vibrational band Band assignment supported by the moment of inertia and g.s.-γ band mixing

16 K π = 8 - isomers and γ-vibrational states in N = 106 isotones 172 Dy 2 + γ: extrapolated from the observed γ-band levels F f ν = τ = exp γ / F ν = K 1/ ν τ W λ K π = 2 + γ-vibrational levels in 172 Dy Unusually low excitation energy, compared to the heavier isotones ( 176 Yb, 178 Hf) Extrapolated energy of the 2 + γ state (671 kev) As low as the 2 + γ state in the γ-unstable nucleus 184 Pt Sufficiently higher than the state Axially-symmetric structure γ-vibrational motion is remarkably enhanced Microscopic effect on the non-axial collectivity is significant

17 Interpretation of γ vibration in the framework of Nuclear DFT Skyrme + pairing energy-density functional (EDF) HFB for the ground state QRPA for the intrinsic excitations K. Yoshida and H. Watanabe arxiv: PTEP in press Selection rules for the non-axial quadrupole matrix elements (Y 22 ) N = 0 or ±2, n z = 0, Λ = K = ±2 Proton Neutron Y 22 U 2

18 Interpretation of γ vibration in the framework of Nuclear DFT E(2 + γ) 172 Dy Neutron 2qp components in 2 + γ HFB+QRPA calculation well reproduces the experimental results Decreasing trend of the 2 + γ energies from 170 Dy 104 to 172 Dy 106 Significant 2qp components in QRPA Proton Not change so much with the neutron number π 2 1/2 + [411] 3/2 + [411] (~0.25), π 2 1/2 + [411] 5/2 + [413] (~0.19) Neutron Isotopic dependence of the 2 + γ energies 3 components play dominant roles beyond midshell (N > 104)

19 Decay spectroscopy of 70 Co

20 COLLABORATION A.I. Morales, G. Benzoni, H. Watanabe, Y. Tsunoda, T. Otsuka, S. Nishimura, F. Brown, R. Daido, P. Doornenbal, Y. Fang, G. Lorusso, Z. Patel, S. Rice, L. Sinclairl, P.-A. So derstro m, T. Sumikama, J. Wu, Z.Y. Xu, L. Coraggio, N. Itaco, A. Gargano A. Yagi, R. Yokoyama, H. Baba, R. Avigo, F.L. Bello Garrote, N. Blasi, A. Bracco, F. Camera, S. Ceruti, F.C.L. Crespi, G. de Angelis, M.-C. Delattre, Zs. Dombradi, A. Gottardo, T. Isobe, I. Kojouharov, N. Kurz, I. Kuti, K. Matsui, B. Melon, D. Mengoni, T. Miyazaki, V. Modamio-Hoybjor, S. Momiyama, D.R. Napoli, M. Niikura, R. Orlandi, H. Sakurai, E. Sahin, D. Sohler, H. Schaffner,R. Taniuchi, J. Taprogge, Zs. Vajta, J.J. Valiente-Dobo`n, O. Wieland, M. Yalcinkaya, Istituto Nazionale di Fisica Nucleare, Sezione di Milano, Via Celoria 16, Milano, Italy Dipartimento di Fisica dell Universita` degli Studi di Milano, Via celoria 16, Milano, Italy IRCNPC, School of Physics and Nuclear Energy Engineering, Beihang University, Beijing , China RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama , Japan Center for Nuclear Study, The University of Tokyo, Bunkyo-ku, Tokyo, Japan Department of Physics, The University of Tokyo, Bunkyo-ku, Tokyo, Japan National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824, USA Instituut voor Kern- en Stralingsfysica, Katholieke Universiteit Leuven, B-3001 Leuven, Belgium School of Computing, Engineering and Mathematics, University of Brighton, Brighton, United Kingdom Department of Physics, Osaka University, Osaka Toyonaka, Japan Department of Physics, University of Surrey, Guildford GU2 7XH, United Kingdom Department of Physics, University of York, Heslington, York YO10 5DD, United Kingdom Department of Physics, Tohoku University, Miyagi , Japan Department of Physics, University of Oslo, N-0316 Oslo, Norway Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro, I Legnaro, Italy IPNO Orsay, Orsay, France MTA Atomki, H-4001 Debrecen, Hungary GSI, Planckstrasse 1, D Darmstadt, Germany INFN Sezione di Firenze, I Firenze, Italy Dipartimento di Fisica delluniversita degli Studi di Padova, I Padova, Italy Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I Padova, Italy Advanced Science Research Center, JAEA, Tokai, Ibaraki , Japan Instituto de Estructura de la Materia, CSIC, E Madrid, Spain Departamento de F sica te orica, Universidad Aut onoma de Madrid, E Madrid, Spain Department of Physics, Istanbul University, Istanbul, Turkey Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Napoli, Italy f Dipartimento di Fisica dell Università di Napoli Federico II, Napoli, Italy EURICA experimental campaign at RIBF in May,

21 Triple shape coexistence in 68 Ni Shape transition and shell evolution also take place within the same nucleus Three 0 + states below 3 MeV in 68 Ni, corresponding to local minima at spherical, oblate, and prolate shapes prolate T 1/2 = 235(23) ns oblate F. Flavigny et al., PRC 91, (2015) spherical Shape coexistence

22 Development of shape coexistence in 70 Ni Monte Carlo shell-model (MCSM) Full pf-g9/2-d5/2 model space A3DA Hamiltonian Y. Tsunoda et al., PRC 89, (R) (2014) Combined effect of the proton-neutron tensor force and changes of major configurations is crucial for driving the shape coexistence Type-II shell evolution Deeper local minimum at prolate deformation level at 1566 kev in 70 Ni C.J. Prokop et al., PRC92, (2015)

23 Purpose of this work How does the β decay of the transitional A = 70 nuclei proceed from the new island of inversion to the Z = 28 closed-shell regime? 70 Fe (Z = 26, N = 44) Deformed» EURICA: G. Benzoni et al., PLB751 (2015) 107» SEASTER: C. Santamaria et al., PRL115 (2015) Ni (Z = 28, N = 42) Shape coexistence 70 Co (Z = 27, N = 43)? Selectivity to populate different shapes? Shape/Shell evolution along the isobaric decay chain?

24 Two long-lived β-decaying states at high and low spins in 70 Co Low-spin β-decaying state in 70 Co isolated via the β decay of 70 Fe Selectively populate low-spin states in 70 Ni Counts / kev Counts / kev Counts / kev Counts / kev x * Energy [kev] Energy [kev] * Energy [kev] x Counts / 2 kev Energy [kev] Counts / 2 kev ms < t < 1.5 s x (e+e-) Counts / kev 607 Counts / 2 kev / Counts / 2 kev 0 < t < 320 ms Late x Energy [kev] x ms < t < 1.5 s x * Counts / 2 kev Energy [kev] Counts / 2 kev (e+e-) Counts / kev Counts / 2 kev / Energy [kev] Counts / 2 kev < t < 320 ms * Early Energy [kev]

25 70 Fe 70 Co: Deformed structure at low excitation energy in 70 Co If spherical, Low-lying levels: πf 7/2-1 νg 9/2 Negative parity 1 + state: πf 7/2-1 νf 5/2-1 E x ~ 1 MeV Strong population of the states at 274 kev: logft = 4.45(13) 1696 kev: logft = 4.95(15) Gamow-Teller transition J π = 1 +

26 70 Fe 70 Co: Deformed structure at low excitation energy in 70 Co proton If spherical, Low-lying levels: πf 7/2-1 νg 9/2 Negative parity 1 + state: πf 7/2-1 νf 5/2-1 E x ~ 1 MeV If deformed, Proton: 1/2 - [321] Neutron: 1/2 - [301] Odd-odd K π = 1 +, 2 + D. Pauwels et al., PRC 78, (R) neutron 1 + state at 274 kev Evidence for a deformed configuration

27 70 Fe 70 Co: Interpretation by Monte-Carlo shell-model calculations MCSM MCSM calculations A3DA Hamiltonian pf + g 9/2 + d 5/2 orbitals Low-lying levels dominated by prolate-deformed configurations States characterized by small deformation appear at 900 kev Hindered Favored logft (MCSM) logft (exp.) >5.4(3) >4.45(13) >4.95(15) Logft Strong population of the and states Highly hindered β feeding to the ground state consistent with the observed decay pattern

28 70 Fe 70 Co: Interpretation by Monte-Carlo shell-model calculations Occupancies of single-particle orbitals for the three 1 + levels of 70 Co MCSM wave functions of the three 1 + states in 70 Co 1 + 1,2: almost identical, involving multiple p-h excitations across the Z = 28 and N = 40 gaps (Type-II shell evolution) Largely prolate deformed shape 1 + 3: dominated by πf 7/2-1 νf 5/2-1 g 9/2 +4 Near spherical shape Gamow-Teller

29 70 Co 70 Ni: Shape-selective β decay low spin 70 Co MCSM prediction J π ( 70 Co) J π (70Ni) logft Strong feeding to the two 2 + states in 70 Ni logft = 5.97(1) for 2 + 1, 5.76(7) for J π = 1 +, 2 +, or 3 + possible for the low-spin β- decaying state in 70 Co Low-spin β-decaying state of 70 Co expected to have J π = 1 + or 2 +.

30 70 Co 70 Ni: Shape-selective β decay (1 +, 2 + ) 70 Co Observation of a candidate for MCSM prediction , Near spherical 0 + 2, Prolate deformed Counts / kev * Counts / 2 kev Energy [kev] Energy [kev] x ms < t < 1.5 s 2105

31 70 Co 70 Ni: Shape-selective β decay (1 +, 2 + ) 70 Co MCSM prediction , Near spherical 0 + 2, Prolate deformed 70 Co (low spin) 70 Ni MCSM Much higher population of than Experiment Slightly prefer to feed than 2 + 1, but almost comparable

32 70 Co 70 Ni: Shape-selective β decay (1 +, 2 + ) 70 Co Four new excited states around 6 MeV Populated with logft ~ 5.7 Preferentially feed the state Similar deformed structure Proton 2qp configurations with K π = 0 +, 1 +, Co (low spin) 70 Ni MCSM Much higher population of than Experiment Slightly prefer to feed than 2 + 1, but almost comparable

33 Summary (part 1) Neutron-rich Dy isotopes have been explored at RIBF as part of the EURICA decay spectroscopy campaign. 172 Dy (N = 106) The most neutron-rich Dy isotope studied to date So far, the heaviest isotope any spectroscopic information obtained at RIBF K π = 8 - isomer (E x = 1278 kev, T 1/2 = 0.71 s) Ground-state rotational band Axial symmetry K π = 2 + states at low excitation energy Enhanced γ vibration Interpretation by Nuclear DFT (HFB+QRPA) 3 neutron 2qp components significant beyond double midshell 168 Dy (N = 102) Analysis is still ongoing

34 Summary (part 2) The level structures of 70 Co and 70 Ni, populated from the decay of 70 Fe, have been investigated using β-delayed γ-ray spectroscopy following in-flight fission of a 238 U beam as part of the EURICA campaign in The experimental results are compared to Monte-Carlo shell-model calculations including the pf+g 9/2 +d 5/2 orbitals. 70 Co (Z = 27, N = 43) Low-spin β-decaying (ground) state with J π = 1 + or 2 + (1 + ) state at E x = 274 kev Prolate-deformed configuration High-spin β-decaying state with J π = (7 - ) 70 Ni (Z = 28, N = 42) state at 1566 kev Spherical shape (1867 kev) and higher-lying levels (~6 MeV) preferentially populated in 70 Co (low spin) 70 Ni

35 Thank you for your attention