Shape Isomerism in 66Ni

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1 Shape Isomerism in S. Leoni, B. Fornal, N. Marginean, M. Sferrazza, Y. Tsunoda, T. Otsuka, et al., University of Milano and INFN sez. Milano, Italy IFJ-PAN, The Ins=tute of Nuclear Physics, Krakow, Poland IFIN HH, Bucharest, Romania Departement de Physique, Universite libre de Bruxelles, Belgium Center for Nuclear Study, University of Tokyo, Japan

2 o Introduction Outline isomers in molecular chemistry o Atomic nucleus shell structure, deformation, potential energy surpace (PES) o Discovery of nuclear fission (shape) isomers o Experimental search for shape coexistence/shape isomers o The unique case of o Relevance for THEORY SHELL Model MICROSCOPIC origin of Nuclear Deformation

3 ISOMERS in chemistry In chemistry, an isomer is a molecule with the same molecular formula as another molecule, but with different arrangement of the atoms. Subgroup: stereoisomers or spa=al isomers Sub-subgroup: conforma=onal isomers (conformers) Sub-sub-subgroup: rotamers

3 C C CH 3 H H H H H Free energy diagram of butane as a

4 Butane molecule C 4 H 10 Conformational isomers C 60 C C rotation C free energy CH 3 CH 3 C C H H 60 rotation H CH 3 C C CH 3 H H H H H Free energy diagram of butane as a function of dihedral angle Rotation about single bond of butane

Potential energy surface (PES) of a nucleus

Z Z TWO-dimensional contour ONE-dimensional

5 Potential energy surface (PES) of a nucleus Parametriza<on of the NUCLEAR SHAPE R( θ, ϕ) = R0[1 + a lm Ylm( θ, ϕ)] l, m If we consider only quadrupole deforma<on a 20 = β cosγ a = (1 22 2)β sinγ β > 0 β < 0 Z Z TWO-dimensional contour ONE-dimensional representation ENERGY Spheroidal Deforma<on β

6 Where do we find secondary minima in the nuclear chart considering only sta<c deforma<on? (no addi=onal degree of freedom involved angular momentum, excita=ons )

7 1953 Already in 1953, Hill and Wheeler discussed possible consequences of the existence of two well separated minima in the potential energy surface for the ground state of the system. Cigare form becoms stable

8 discovery of the first spontaneously fissioning isomer in 242 Am with a half-life 14 msec C. M. Polikanov et al., Zh. Eksp. Teor. Fiz. 42, 1464 (1962) [Sov. Phys.- JETP 15, 1016 (1962)]

9 Liquid Drop Model

Shape isomers in actinides 50 82 126 o HIGH Poten<al BARRIER o Nucleus trapped In the second

10 Shape isomers in actinides o HIGH Poten<al BARRIER o Nucleus trapped In the second minimum o Spontaneous fission from the second minimum TWO EXCEPTIONS

11 SHAPE ISOMERS very peculiar metastable states o HIGH Poten<al BARRIER o Nucleus trapped In the minimum o very retarded photon decay (10 7 hindrance) 236,238 U 95% γ 5% B(E2)=1.54 x10-7 W.u.!!! Structures living in separate worlds MAIN FINGER PRINT: hindrance of deexcisng transisons Can OTHER (lighter) nuclei exhibit these features?

12 SEARCH for SHAPE ISOMERS in LIGHTER nuclei: o MOST CLEAR-CUT cases of SHAPE Coexistence o a PROBE of MICROSCOPIC origin of nuclear deforma<on within a pure SHELL Model Approach Ideal Cases are 0 + states to avoid ambiguity given by spin effects (Ac<nides are NOT doable by SHELL Model )

13 SHAPE Coexistence in Atomic Nuclei Appearence of diﬀerent shapes at low excitason energy K. Heyde and J. L. Wood, Rev. Mod. Phys. 83, 1467 (2011) Spherical Oblate Prolate 186Pb Shape Isomers in acsnides Polikanov A. Andreyev et al., Nature 405 (2000) Through the last 40 years of experimental acsvises, the concept has evolved: 1) exo<c rarity (1970 ) 2) islands of occurrence (1990 ) 3) current believe: occurrence in all (but the lightest) nuclei

Z=50 235 U target 0.3 Z=28 N=50 N=82 241 Pu target 0.2 N=60 0.3 0.1 100 Zr 0.2 0.0 0.0 0.1 0.

14 Z= U target 0.3 Z=28 N=50 N= Pu target 0.2 N= Zr B(E2) W.u B(E2) 63 W.u. 0 + B(E2) 69 W.u Sr 100 Zr 102 Mo

15 Z= U target E. Clément, M. Zielińska et al., Phys.Rev. Lej. 116, (2016) N= Pu target N=60 N=50 B(E2)=16 W.u. 96 Sr 98 Sr B(E2)=93 W.u. No retardason in γ decay is observed!!!! Poten<al barrier NOT sizable enough to prevent fast shape changes

16 PredicSons for SHAPE ISOMERS - Mean Field Based Macro-Microscopic Model P. Moeller et al Global Calculation Searching for Nuclear Shape Isomers Study of 7206 nuclei from A=31 to A= actinides 1989 Microscopic Hartree-Fock plus BCS calculations 1989 Barrier hight Energy of second minimum 64 Cr Fe Zn

PredicSons for SHAPE ISOMERS SHELL Model Based [Otsuka group and Nowacki, Lenzi, Poves, ] state-of-the-art SHELL Model: possible for A <= 100 new calcula<ons scheme, very powerfull computer

17 PredicSons for SHAPE ISOMERS SHELL Model Based [Otsuka group and Nowacki, Lenzi, Poves, ] state-of-the-art SHELL Model: possible for A <= 100 new calcula<ons scheme, very powerfull computer Inves<ga<on of MICROSCOPIC NATURE - wave func<ons, B(Eλ/Mλ), Monte Carlo SHELL Model (T. Otsuka s Group K computer 10 6 processors) 78 : FULL pf + g 9/2 + d 5/2 for both neutrons and protons oblate oblate prolate prolate Z= stable N=40 N=50 Y. Tsunoda et al., PRC 89 (2014) R

18 Experimentally No retardason is found in 68 and 70 B(E2) 2.4 W.u. prolate B(E2) oblate 7 W.u. prolate B. P. Crider et al., Phys. LeP. B 763, 108 (2016)

19 PredicSons of four models à shape isomerism in Microscopic Hartree-Fock-Bogoliubov Microscopic Hartree-Fock plus BCS 1989 Barrier hight 1989 Energy of second minimum 64 Cr Fe Zn Macro-Microscospic Model Monte Carlo Shell Model

20 MONTE CARLO SHELL MODEL Calculations Y. Tsunoda and T. Otsuka, Univ. of Tokyo State-of-the-art Shell Model calculations possible by employing new calculations schemes and very powerful computing systems (K computer processors) prolate W.u FULL pf + g 9/2 + d 5/2 for both neutrons and protons W.u. 4.1 W.u. oblate Detailed Microscopic Inves<ga<on: o Wave func<ons o B(Eλ/Mλ), 0 +1

MONTE CARLO SHELL MODEL Calculations Y. Tsunoda and T. Otsuka, Univ. of Tokyo 0 +4 prolate 0 +3 0 +2 0.006 W.u. 0.01 W.

21 MONTE CARLO SHELL MODEL Calculations Y. Tsunoda and T. Otsuka, Univ. of Tokyo 0 +4 prolate W.u W.u. 4.1 W.u. oblate Circles: MCSM basis vectors projected on PES (T-Plot) A quadruplet of 0 + states!!!! 0 +1

Decay Scheme of R. Broda et al., Phys. Rev.

74 (t,p) 0 +4 0 +3 0 +2 0 +4 0 +3 0 +2 prolate oblate 0.

22 Decay Scheme of R. Broda et al., Phys. Rev. C 86, (2012) Monte Carlo SHELL Model 0.15(2) W.u (7) W.u (9) W.u (9) W.u (t,p) prolate oblate (4) W.u Excited states energies à One-to-one correspondence (including 0 + states!) B(E2/M1) (from our Bucharest EXP) à very well reproduced!!

23 β-decay populason of D. Pauwels, P. Van Duppen et al., ARIS-2011 Conference Monte Carlo SHELL Model 3.1(6) 5.3(2) prolate 29(3) 4.4(1) (1) 5.5(4) oblate 63(4) 4.8(1) I β (%) log(l) EXP 4.3 log(l) MCSM General agreement with β-decay branches Feà Co à 0 +1 model predicsons: popula<on of 0 + and 2 + states from Co g.s

Our Bucharest Experiment (@IFIN HH) 18O + 64 à 16O + (2n

strongly suppressed Z=28 64 ROSPHERE N=40 γ 64 18O (39 MeV)

75% eﬀ o THICK Target 5 mg/cm2 o PLUNGER - 12 distances

24 Our Bucharest Experiment HH) 18O + 64 à 16O + (2n Transfer - 1 MeV below Coulomb Barrier) σ() few mb - FUSION strongly suppressed Z=28 64 ROSPHERE N=40 γ 64 18O (39 MeV) 16O γ 14 HPGe - 1.1% eﬀ 11 LaBr3(Ce) % eﬀ o THICK Target 5 mg/cm2 o PLUNGER - 12 distances From 10 to 3000 µm v/c 2.2 % TOF of 155 ps in 1 mm > 1.5 month 30 pna beam current

25 18 O+ 64 à 16 O+ E beam = 39 MeV 2n transfer below Coulomb Barrier at IFIN HH Bucarest THICK TARGET gate: 1425 kev 1.4 ps (DSAM) (t,p) THICK TARGET, gate: 1425 kev ps ps 1245 All transi<ons belong to!!

26 18 O+ 64 à 16 O+ E beam = 39 MeV 2n transfer below Coulomb Barrier at IFIN HH Bucarest THICK TARGET gate: 1425 kev 1.4 ps (DSAM) (t,p) THICK TARGET, gate: 1425 kev ps ps ps 1245 All transi<ons belong to!!

27 0 +4 prolate (7) ps 134(9) ps 7.6(8) ps W.u W.u. 4.1 W.u. oblate

28 !!!!!!!!!!!!! B(E2) ~ 0.2 Wu B(E2) = 0.1 Wu B(E2) = 4.3 Wu 2 TRANSITIONS BELOW 1 W.u.!!!! W.u W.u. 4.1 W.u. prolate oblate

29 PROTON NEUTRON B(E2) ~ 0.2 Wu B(E2) = 0.1 Wu B(E2) = 4.3 Wu 2 TRANSITIONS BELOW 1 W.u.!!!! W.u W.u. 4.1 W.u. prolate oblate is (very similar to 0 + 1): HINDRANCE due to cancellason of matrix elements à independent measurement of τ(0 + 3) at ISOLDE - B. Olaizola, L. Fraile et al., PRC95, (R) (2017) Shell Model with LNPS interac=on A. Poves and F. Nowacki 0 +1

30 PROTON NEUTRON PROTON NEUTRON B(E2) ~ 0.2 Wu B(E2) = 0.1 Wu B(E2) = 4.3 Wu 2 TRANSITIONS BELOW 1 W.u.!!!! W.u W.u. 4.1 W.u. SHAPE ISOMER Like!! prolate oblate is prolate: HINDRANCE due to shape change through high poten<al barrier!!!!

PROTON NEUTRON PROTON 0 +1 0 +2 0 +3 0 +4 0 +1 0 +2 0 +3 0 +4 NEUTRON 0 +4 SHAPE ISOMER Like!

31 PROTON NEUTRON PROTON NEUTRON 0 +4 SHAPE ISOMER Like!! prolate Type II SHELL EvoluSon (tensor force) s 1/2 d 5/2 f 5/2 STABILIZATION of DEFORMED Local Minima ê SHAPE COEXISTENCE W.u W.u. 4.1 W.u. oblate WITHIN the SAME nucleus change of major configura=ons: sizable excita=ons of ν in g 9/2 reduced proton spin-orbit spli`ng is prolate: HINDRANCE due to shape change through high poten<al barrier!!!

32 : lightest and unique example - apart from the ac=nides of 0 + deformed state deexci<ng via HINDERED γ transi<on a SHAPE-ISOMER-like structure!!!! A probe of TYPE II SHELL EvoluSon: rearrengement of nucleons in orbitals causes emergence of deforma<on ** Thank You for the Attention ** BORMIO

PRIZES for Young Speakers offered by CAEN Deadline for ABSTRACT Submission 20 Sep. 2017 Organizers: A. Bracco, F. Camera, G. Colò, S.

33 PRIZES for Young Speakers offered by CAEN Deadline for ABSTRACT Submission 20 Sep Organizers: A. Bracco, F. Camera, G. Colò, S. Leoni; Scient. Secretaries: F. Crespi, X. Roca-Maza Web-Page:

Shell evolution and nuclear forces

1 st Gogny Conference Campus Teratec, Bruyères-le-Châtel Dec. 8-11 (9), 2015 Shell evolution and nuclear forces Takaharu Otsuka University of Tokyo / MSU / KU Leuven Priority Issue project (field 9) by