agata physics workshop istanbul, turkey may 4-7, 2010 g. duchêne deformation in n=40 nuclei g....

AGATA Physics Workshop Istanbul, Turkey May 4-7, 2010

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Deformation in N=40 nuclei

G. Duchêne , R. Lozeva, C. Beck, D. Curien, F. Didierjean, Ch. Finck, F. Nowacki, K. Sieja

IPHC StrasbourgC. Domingo-Pardo, J. Gerl and the GSI group

GSI DarmstadtD. Verney, F.Azaiez, S. Franchoo, F. Ibrahim, F. Le Blanc, I. Matea,

M. Niikura, I. StefanIPN Orsay


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Deformation in Fe and Cr nucleiE. Caurier et al., Eur. Phys. J A15 (2002) 145

Fe

Cr Cr


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68Ni

Is 68Ni a magic nucleus ? Increase of the 21

+ excitation energy Reduction of the B(E2) value

No pronounced irregularity in the 2-neutron separation energy

Strong 2p-2h component -> excitation of a neutron pair into g9/2 orbital

Major part of the B(E2) strength around 5 MeV

Deformation in 68Ni 68Ni gs is spherical (Gaudefroy et al.,

Phys. Rev. C80 (2009) 064313) Main 01

+ state configuration is 4p-4h Does not generate much

deformation

K. Langanke et al., Phys. Rev. C67 (2003) 044314


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In the vicinity of 68Ni

67Co Collective 1p-2h proton intruder First excited ½- state with large

quadrupole deformation β ~ 0.25-0.4D. Pauwels et al., Phys. Rev. C 78, 041307(R)

(2009)

69Cu Measured magnetic moment of 13/2+

state Considerable proton excitations

across the Z=28 proton gap Deviate from sphericityG. Georgiev et al., J. Phys. G: Nucl. Part. Phys.

28, 2993 (2002)

70Zn Given as a γ-soft nucleus (Gaudefroy et

al., Phys. Rev. C80 (2009) 064313)

Hunt for deformation with np-nh

configurations (n=6, 8) at higher

excitation energy


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Shell-model calculations

Valence space 40

20Ca20 core π: f7/2 + fp shell υ: f7/2 frozen + fp shell (p3/2 frozen)+ g9/2 + d5/2

68Ni: 8p-8h excitations 70Zn: 6p-6h excitations

Huge matrices to diagonalise~(500 106)² to more than (109)²

Several days calculation

Results 68Ni 8p-8h config:

B(E2)down ~ 690 e²fm4

Q2 = -49 e.fm²

β2 ~ 0.32E* ~ 13 MeV

6p-6h config:B(E2)down ~ 190 e²fm4

Less deformation drivingE* ~ 10 MeV

70Zn 6p-6h config:B(E2)down ~ 695 e²fm4

Q2 = -48 e.fm²

β2 ~ 0.32E* ~ 10 MeV

All configurations are spread over many states when configuration mixing is allowed !

Mean field calculation in the β-γ plan


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Angular momentum and particle rates

High-angular momentum states feeding Several nucleon knock-out lead to « high-

spin » transfers 8+ fed ~10 time less than 2+ state Hypothesis: deformed structure feeding of

10% at 8 ħ

Nuclei production rate Primary beam: 76Ge -> Imax = 3 108 p/s Primary Be/Nb target of 2.5 g/cm² Al degrader of 1.5 g/cm² Intermediate fragments: 73Ga or 72Zn Rates calculations (slits cuts in S1, S3, S4)

AGATA Lycca

105 Hz/wire

104 Hz

Primary beam (p/s)

Intermediate

fragment

Transmissio

n

S4 rate (p/s)

ReactionFinal

nucleus

Production rate

(p/s)

7 106 p/s 7331Ga 30% 104

fragmentation

6828Ni 0.3

1p-2n knock-out

7030Zn 18

3 107 p/s 7230Zn 42% 104

fragmentation

6828Ni 2.5

2n knock-out 7030Zn 35


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Gamma-ray statistics

S’2 geometry Full configuration: 10TC + 5DC -> 17% Min. configuration: 5TC + 3DC -> 9%

Intermediate fragment 72Zn; 1.5 MeV gamma ray

Experiment duration: 7 days

Projectile

Nucleus of

interest

AGATA config.

γ-rate (min-1)

Total counts singles

in 7 days

γ γ -rate (min-1)

Total counts doubles

in 7 days

72Zn

68Ni2.5 p/s

Full 0.19 1900 0.024 244

Min 0.10 1000 0.0068 69

70Zn35 p/s

Full 2.66 26600 0.34 3400

Min 1.40 14000 0.095 950


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Ni-Zn-Ge

Gaudefroy et al., Phys. Rev. C80 (2009) 064313

J. Van de Walle et al., Phys. Rev. Lett.99 (2007) 142501


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Tensor force

Attractive between spin-flip orbitals

Attractive interaction πf5/2-νd5/2

Relaxed when removing protons from πf5/2 orbital

Excitation energy of νs1/2 state apparently decreases vs νd5/2 state

π ν

f7/2

p3/2

f5/2

p1/2

g9/2

d5/2

s1/2

g7/2

j+1/2

j-1/2

agata physics workshop istanbul, turkey may 4-7, 2010 g. duchêne deformation in n=40 nuclei g....

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