Shape coexistence in the - PowerPoint Presentation

Shape coexistence in the 78 Ni region: intruder 02 state in 80GeALTO @ IPN Orsay Andrea Gottardo Nuclear Structure 2016 +

index The N=50 region Intruder states: a probe of collectivity-spherical gap interplay What is known around N=50 Phenomenological predictions Electron spectroscopy in 80 Ge Perspectives Courtesy of D. Verney

The N=50 region Sr88 Rb87 Kr86 Br85 Se84 As83 Ge82 Ga81 Zn80 Cu79 Ni78 Ni77 Ni71 Ni72 Ni73 Ni74 Ni75 Ni76 Ni70 Ge76 Ge74 Y89 Zr90 As75 Se76 Se77 Se78 Se80 Se82 Br79 Br81 Kr78 Kr80 Kr82 Kr83 Kr84 Rb85 Sr86 Sr87 Sr84 Zr91 Zr93 Zr92 50 fp proton space Quasi-SU(3) scheme: gds shells, similar case to N=20 with f 7/2 -p 3/2

The N=50 Spin-orbit shell closure Reduction of the N=50 spherical gap from N=51 isotones mass ? K. Sieja et F. Nowacki, Phys. Rev. C 85, 051301(R) (2012)p -h states across N=50 in N=49 and N=50 isotones: minimum at Z=32CONSTANT GAP e d 5/2 – e g 9/2 (MeV)NiZnGeSe Kr Sr Duflo Zuker gap PRC59 (1999) 90Zr =4,7 MeVDuflo Zuker gap 78Ni =5,7 MeV « standard » local minimum at Z=32Zr« graphical »M.-G. Porquet and O. Sorlin, Phys. Rev. C 85, 014307 (2012)

2 p -2h Intruder states as probes of gap 2 particle – 2 hole across N=50 Spherical gap (2p-2h) : energy cost Correlations by breaking the core: energy gain Z=28 N=50 fp protons neutrons d 5/2g9/2 s1/2

Shape coexistence in the nuclear chart 78 Ni Modified from Heyde & Wood Rev. Mod. Phys. 83 (2011) 1467 ? N=20 Z=50

Intruder states IN N=49 isotones Intruder states (1p-2h) in N=49 states: Minimum at Z=34Inversion 1/2+ - 5/2+Pure s1/2 wave function ? Shape ?What is then happening to the even-even nuclei: low-lying 0 + states ? X. F. Yang et al. Phys. Rev. Lett. 116, 182502 (2016) d 5/2 g 9/2 s 1/2 N=50

Systematics of 0 + states in Z=32 and N=50 Ge isotopes and N=48 isotones seem to cross around the energy of ~ 600 keV in 80 Ge N=49 isotones: intruder 0 + at ~ 1300 keV Coexistence of triaxial shapes in 72Ge: A.D. Ayangeakaa et al., Phys. Lett. B 754 (2016) 254–259 Modified from D. Verney et al. Phys. Rev. C 87, 054307 (2013)d5/2g9/2 s1/2 N=50

Energy of intruder (2p-2h ) 0+ states   : from 2 n separation energies   Where: : IBM-2 approximation   ; : graphical method   The (2p-2h) 0 + states are going down in energy The monopole contribution flattens out the midshell Z=34 quadrupole minimum 0 + ExpJ. L. Wood et al., Phys. Rep. 215, 201 (1992).D. VerneyN=48K. Heyde et al.: PLB176, 189 (1986) d5/2g9/2 s1/2 N=50 gap

Experimental setup: ALTO @ IPN ORSAY ISOL facility at Orsay:50 MeV, 10 μA e- beam, UCx target 1011 fissions/sSurface and laser ionization PARRNe on line mass separator BEDO - decay station

THE PARRNE measurement point (surface ionized) 80 Ga beam (10 4 pps ) tape photo multiplier Ge Plastic scintillator Cryogenic finger SiLi collection point Ge counting position b -detection LN2-cooled Si(Li) e - detector g -detection Search for E0 transitions ε (1MeV)= 0.7% ε= 20%εe-= 14%Courtesy of D. Verney

ELECTRON SPECTRUM 0 + 1 2 + 1 0 + 2 0 E2659 639 E0 80 Ge No transition at 639 keV which could justify electron conversion at 628 keV

ELECTROn –gamma coincidences 0 + 1 2 + 1 0 + 2 0 E2659639 E0 80 Ge   (2 + x)(2403)Electron-γ coincidences to Confirm spectroscopyFuture studies of the structure of the second 0+(E2)

Results and perspectives O ur resultA. Gottardo , D.Verney et al.,Phys. Rev. L ett. 116, 182501 (2016) Shape coexistence in 78 Ni ? Monopole evolution towards Z=28: mass measurement in 83 Zn Reduction the Z=28 gap (increased quadrupole) ? Possibility of finding a (2p-2h) 0+ state in 78Ni around 2.5 - 3 MeV

ISOMER SHIFT IN N = 49 isotones X. F. Yang et al. Phys. Rev. Lett. 116, 182502 (2016) g 9/2 s 1/2 N=50 The 1/2 + state in 79 Zn has a dominant ν (g 9/2 -2 s1/2) character Large isomer shift. Interpreted as large deformation (β ~0.22) of the intruder state

CONCLUSIONS and perspectives Electron spectroscopy reveals E0 transition in 80Ge pointing to a low-lying 0+ stateThe state is consistent with an intruder (2p-2h) excitation, revealing shape coexistence in the N=50 region. A measurement on 79Zn also saw a large isomer shift from intruder states The N=50 gap evolution could imply shape coexistence in 78 Ni, with a second 0 + state around 2.5 - 3 MeV F. Nowacki, A. Poves et al. arXiv 1605.05103v1 (2016)

2-state repulsion toy model Delta interaction (s=0.3)

ρ (E0) and configuration mixingτ<50 ns : ρ 2(E0) >0.1 For comparison : 30Mg: τ(E0) = 400(100) ns : ρ2 (E0) = 0.03 (1)

spherical gap from masses: graphical method The shell gap N=50 is overestimated (~300 keV) by the Sn(N+1) -Sn(N) differenceGraphical method by K. Heyde et al.: PLB176, 189 (1986) S n (N=50) - S n (N=51 ) Sn(N=50) - Sn(N extr) Shell gap: energy to separate the 51th neutron on 82Ge, NOT 83 Ge e d 5/2 – eg9/2 (MeV)Ni ZnGeSeKrSr Duflo Zuker gap PRC59 (1999) 90Zr =4,7 MeVDuflo Zuker gap 78Ni =5,7 MeV « standard »local minimum at Z=32Zr« graphical »

N=26 30Mg : a similar case W. Schwerdtfeger et al., PRL 103, 012501 (2009)

Quadrupole contribution Quadrupole energy in IBM-2:   Where: (orbital degeneration) number of active bosons ( k ~-0.22 MeV n ormal value in this region)  So: (average between the 28-50 and the 50-82 spaces )    K. Heyde et al., Nucl. Phys. A466, 189 (1987)K. Heyde et al., Nucl. Phys. A484, 275 (1988)  

Graphical method K. Heyde et al., Phys. Lett. B 176, 255 (1986) [...] this 0+ state lies below the first-excited 2+ state. Within a deformed mean-field approach this is equivalent to a macroscopic phase change from a spherical to an oblate shape. A.N. Andreyev, Nature 405, 430 (2000)

Excited 0+ states in 82 ge J. K. Hwang et al. Phys. Rev. C 84, 024305 (2011)82Ge in spontaneous fission. Highly deformed structures observed on the excited 0+ states