nuclear collectivity and shape evolution in exotic nuclei

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Nuclear collectivity and shape evolution in exotic nuclei

Wolfram KORTENCEA Saclay

DSM/IRFU/SPhN

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Shapes and shells in exotic nuclei

Prolate

Oblate

Quadrupole deformation of the nuclear ground states

M. Girod, CEA Bruyères-le-Châtel

Dominance of prolate ground state shapes over most of the nuclear chart Islands of oblate nuclei and shape coexistence (N~Z, A~100, …) Erosion of shell gaps leads to (strongly) deformed nuclei at N=20, 28 and 40

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nEvolution of collectivity around N=40

Persistence of N=40 sub-shell closure beyond 68Ni ? correlations stronger than N=40 gap for Z28 increased collectivity with filling of g9/2

Previous experimental results: Coulomb excitation of 78-82Ge at ORNL / HRIBF E. Padilla-Rodal et al., PRL 94, 122501 (2005) Coulomb excitation of 74-80Zn at CERN / ISOLDE J. Van de Walle et al., PRL 99, 142501 (2007) J. Van de Walle et al., PRC 79, 014309 (2009)New experimental approach Lifetime measurements after MNT/DIC B(E2) in Fe EXOGAM/VAMOS at GANIL B(E2) in Zn AGATA/PRISME at LNL

N=50

Z=28

N=40

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nExperimental methods: Coulomb

excitationCoulomb excitation of 74-80Zn at CERN / ISOLDE

AZn on 108Pd/120Sn at ≈2.8 MeV/u integral measurement excitation probability via normalization to target one observable: (2+), two unknowns: B(E2), Qs

20 ps

28.5 ps25 ps

74Zn

two unknowns: B(E2; 0+ 2+) Qs(2+)

If

Ii

Mf

= 0 !

J. Van de Walle et al., PRL 99, 142501 (2007)

J. Van de Walle et al., PRC 79, 014309 (2009)

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nCollectivity in neutron-rich nuclei around

N=40

-2p : 62Fe 74Zn-2p+2n: 64Fe 76Zn

238U + 64Ni @ 6.5 MeV/uVAMOS + EXOGAM

76Ge + 238U @ 7.6 MeV/uPRISMA + AGATA Demo.

Recoil-Distance Doppler-shift (RDDS) lifetime measurements in nuclei produced by multi-nucleon transfer or deep-inelastic reactions

N=40

N=50Z=28

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nRDDS experiment in inverse kinematics at VAMOS

QQ

D

45°

drift chamber: x,y

drift chamber: x,y

Se-D: trigger, t1

ionisation chamber: Esilicon wall: E, t2

64Fe

64Ni

Mgv1

v2

1x180°3x135°

5x90°

238U, 6.5 MeV/u

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The Recoil-Distance Doppler-Shift technique

baft ~ 8.5%bbef ~10%

Eg

E’g Eg

E’g

J. Valiente-Dobón et al., PRL 102 (2009) 242502

Differential RDDS technique combined with deep-inelastic (or multi-nucleon transfer) reactions was pioneered at LNL using the CLARA-PRISMA set-up

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64Fe

Lifetimes in neutron-rich Fe isotopes

238U + 64Ni @ 6.5 MeV/u

J. Ljungval et al., PRC C 81, 061301(R) (2010)

62Fe 64Fe

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f7/2

p3/2f5/2

p1/2

g9/2

d5/2

66Fe 5040

28

Importance of neutron g9/2 (and d5/2) intruder orbitals

Collectivity in neutron-rich Fe isotopes

J. Ljungval et al., PRC C 81, 061301(R) (2010)W. Rother et al., PRL 106, 022502 (2011)

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nCollectivity in neutron-rich nuclei around

N=40

-1p : 63Co -1p+2n: 65Co

238U + 64Ni @ 6.5 MeV/uVAMOS + EXOGAM

N=40

N=50

Lifetime measurements in neutron-rich Fe and Co isotopes

Z=28

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Fe and Ni Core coupled states ?Structure of the ground state ?

Structure of odd-mass Co isotopes

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nLifetime measurement in 63,65Co

“Fe-like” 3/2-7/2-

transition

A. Dijon et al., PRC 83, 064321 (2011)

Direct lifetime extraction possible

T1/2=15.4 ± 1.8 psB(E2)= 3.71 ± 0.43 W.u

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nLifetime measurement in 63,65Co

lifetime extraction requires selection in excitation energy

T1/2=0.9 ± 0.4 psB(E2)= 12.2 ±5.4 W.u

“Ni-like” 9/2-7/2-

transition

A. Dijon et al., PRC 83, 064321 (2011)

Direct lifetime extraction possible

T1/2=15.4 ± 1.8 psB(E2)= 3.71 ± 0.43 W.u

“Fe-like” 3/2-7/2-

transition

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nCollectivity in neutron-rich nuclei around

N=40

-2p : 74Zn-2p+2n: 76Zn

76Ge + 238U @ 7.6 MeV/uPRISMA + AGATA Demo.

Lifetime measurements in neutron-rich Zn and Co isotopes

N=40

N=50Z=28

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Lifetime measurement in neutron-rich Ni, Cu and Zn isotopes

Spokespersons: A. Goergen (Saclay), M. Doncel (U. Salamanca), E. Sahin (LNL)

AGATA experiment performed in June 2010 at the LNLusing multi-nucleon transfer reaction (76Ge + 238U)

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The PRISMA spectrometer at LNL

QuadrupoleDipole

MCP

MWPPAC IC

Angular range: -30º to 140º

X-Y, time

X-Y, time E, E

AGATA

6.5 m (TOF)

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Charge state determination and selection

Z identification

Mass separation(all distances together)

Particle identification with PRISMA

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Multi-nucleon transfer reactions in direct kinematics: 76Ge+238URecoil-Distance Doppler Shift (RDDS) experiments differential plunger

Lifetime experiments with AGATA at PRISMA

76Ge beam (577 MeV, 0.3pnA)238U target (1.4 mg/cm2)Ta backing (1.2mg/cm2)Nb degrader (4 mg/cm2) 50-70 khZ Ge singles rate

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nRDDS with EXOGAM vs. AGATA Demonstrator

Exogam

v

AD at 14cm

AGATA Demo.

6 times more counts for same peak separation

peak separation for all angles

180 detector at 11 cm135 detectors at 14.5 cm

GEANT 4 simulationand AGATA tracking(J. Ljungvall)

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nRDDS spectra of neutron-rich Zn isotopes

C. Louchart et al, to be published

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nRDDS analysis: Differential Decay Curve method

and

v = 30 mm/ps

100 mm

200 mm

500 mm

1000 mm

1900 mm

C. Louchart et al, to be published

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nRDDS analysis: Differential Decay Curve method

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Collectivity in neutron-rich Zn isotopes

References:[1] J.K. Tuli, Nucl. Data Sheets 103 (2004) 389[2] B. Prytychenko arXiv:1102.3365v2 (2011)[3] D. Muecher et al., PRC 79 (2009) 054310[4] S. Leenhardt et al., EPJ A 14 (2002) 1[5] J. Van de Walle et al., PRC79 (2009) 014309[6] M. Niikura et al., PRC (2012) in press [7] E. Clement, priv. comm.

C. Louchart et al, to be published

20 ps

28.5 ps25 ps

Quadrupole moment Q(2+) of 74Zn

Preference for oblate shape of 74Zn

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J.-P. Delaroche et al, PRC 81, 014303 (2010)M. Honma et al, PRC 80, 064323 (2009)

74Zn

HFB D1SFrom lifetime experimentM. Niikura et al. arXiv : 1105.4072v1 (2011)

J. Van de Walle et al, PRL 99, 142501 (2007)J.-P. Delaroche et al, PRC 81, 014303 (2010)M. Honma et al, PRC 80, 064323 (2009)

74Zn

Quadrupole collectivity of 74Zn

B(E2) in accordance with shell modeland HFB D1S calculation

Q(2+) >0 indicates “oblate” shapenot supported by the shell modelnor the HFB D1S calculation

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Maximum of collectivity at N~42 B(E2; 2+ 0+) values in agreement

with previous measurements

lower B(E2; 4+ 2+) values withminimum at N=44

Discrepancy for t(4+) in 74Zn with previous (Coulomb

excitation) measurement

70Zn: D. Mücher et al. PRC 79 054310 (2009)74Zn: J. Van de Walle et al. PRC 79 014309 (2009)

Collectivity in neutron-rich Zn isotopes

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B(E2; 2+->0+) values are in agreement with shell model calculations

Beyond mean field calculation over estimate the collectivity in particular forB(E2; 4+->2+) values

Shell model calculations do not reproduce the trend of the systematics for B(E2; 4+->2+) values

Collectivity in neutron-rich Zn isotopes

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Collectivity in neutron-rich Zn isotopes

R(E2) <1 for all Zn isotopes (except 70Zn at N=40)similar to Ca and (partially) Cr isotopes,

but different from Ti (Z=22)

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nCollectivity in neutron-rich nuclei around

N=40

-3p-2n : 71Cu-3p: 73Cu

76Ge + 238U @ 7.6 MeV/uPRISMA + AGATA Demo.

Lifetime measurement in neutron-rich Zn and Cu isotopes

N=40

N=50Z=28

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Experimental results: 71Cu

M. Doncel et al, to be published

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Shell-model calculations using the fpg valence space do not reproduce the B(E2) values for Cu isotopes.

Inclusion of the neutron d5/2 orbital

(1) I. Stefanescu et al., Phys. Rev. Lett 100 (2008) 112502(2) N.A. Smirnova et al., Phys. Rev. C (2004) 044306

LNPS interaction: shell-model calculations using an enlarged valence space: pf-shell orbitals for protons and f5/2, p1/2, p3/2, g9/2 and d5/2 orbitals for neutrons.

(3) K. Sieja et al., Private Communication.

Experimental results: 71Cu

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Occupation numbers for neutrons and protons:

The inclusion of the neutron d5/2 orbital, which is the SU(3) partner of the g9/2 orbital, leads to an enhancement of the quadrupole contribution. B(E2) values are well reproduced taking into account this contribution not considered in previous shell-model calculations.

Different behavior of the proton p3/2 and f5/2 orbitals

Inclusion of the neutron

d5/2 orbital

Different character for

the 7/2 - excited states

Experimental results: 71Cu

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nShape evolution in the A~100 region

96Sr 98Sr 100Sr 102Sr 104Sr94Sr92Sr

100Zr 102Zr 104Zr 106Zr98Zr96Zr94Zr

94Kr 96Kr 100Kr 102Kr98Kr92Kr90Kr

92Se 94Se 96Se 98Se90Se

96Mo 98Mo 100Mo 102Mo 104Mo 106Mo 108Mo

100Ru 102Ru 104Ru 106Ru 108Ru

rapid shape changes and shape coexistence expected accessible with HIE-Isolde and SPIRAL-2

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nIn-flight studies of fission fragments at

GANIL

QQ

D

drift chamber: x,y

drift chamber: x,y

Se-D: trigger, t1

ionisation chamber: Esilicon wall: E, t2

110Ru

9Be

Mgv1

v2

1x180°3x135°

5x90°

238U, 6.5 MeV/u

Fission fragment production/identification with VAMOSGamma-ray detection with EXOGAMRDDS experiment using plunger (spring 2011)New results for several neutron-rich nuclei112Ru, 118Cd, many odd-mass isotopes

110Ru

A. Shrivastava, F. Rejmund et alPhys. Rev. C80 091305(R) (2009)

pioneered by F. Farget et al. (see talk Fr morning)

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Fission fragment distribution

9Be(238U,ff)X at 6.5 MeV/u

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nPreliminary fission fragment gamma-ray

spectra

9Be(238U,ff)X at 6.5 MeV/u

98-102Zr; 104-108Mo; 110-114Ru114-118Pd; 118-122Cd

100Zr

102Zrt(I≥4+)

104Mo

106Mo

108Mot(I≥4+)

110Rut(I≥4+)

112Rut(I≥4+)

114Rut(I≥2+)

2+

4+

4+

4+2+ 2+ 2+

4+

4+

4+

4+

2+

2+

6+

8+

10+

6+

8+

8+

6+

6+

6+

8+

2+

2+

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Summary and perspectives Application of Recoil-Distance Doppler-Shift Method to deep-inelastic and fusion-fission reactions is a powerful tool to study (moderately) neutron-rich nuclei Onset of collectivity in the Fe isotopes below 68Ni starts already around N~38 and requires inclusion of d3/2 orbital in shell model calculations Neutron-rich Zn isotopes show tendency towards oblate deformation in contrast to theoretical expectations; B(E2) ratios of 4+ and 2+ decays are systematically < 1

Perspective for strong progress when using RDDS technique with AGATA@VAMOS (2014) and complementary Coulomb excitation experiments using SPIRAL2 and HIE-Isolde

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Thank you

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33.6 μm

99 μm

2 0

4 2

6 4

Recent 72Zn measurement at GANIL

0+

2+

(4+)

(6+)

652.68

846.75

1153.3

72Zn τ [ps] B(E2) [e2fm4]

2+ 22.6±7.0 304±94

4+ 8.1±1.8 232±51

6+ 3.3±1.6 120±56

17.9(1.8) M. Niikura et al. Accepted PRC (2012)18.2(1.4) C. Louchart et al.

5.9(7) C. Louchart et al.

I. Celikovic et al. GANIL-VINCA

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nQuadrupole moments in neutron-rich Zn

nuclei

focus of ISOLDE experiment was on 80Zn new Coulex measurement (~ 3 days)

improve precision for 74,76Zn significantly obtain data for 72Zn (planned in summer 2012)

Combined with results from ISOLDE CoulexRDDS lifetime measurement will yield quadrupole moments for 2+ states in 74,76Zn.

J. Van de Walle et al., PRC 79, 014309 (2009)

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nDSAM lifetime measurement in

72Zn

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All nuclei 20<Z<40Non-magic nuclei 40<Z<80

R.B. Cakirli et al. PRC 70, 047302 (2004)

vibrator

rotor

possible explanation as transition fromseniority regime to collective motion ?J.J. Ressler et al. PRC 69, 034317 (2004)