Deformation in N=40 nuclei G. Duch

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Deformation in N40 nucleiG. Duchêne , R.
Lozeva, C. Beck, D. Curien, F. Didierjean, Ch.
Finck, F. Nowacki, K. SiejaIPHC StrasbourgC.
Domingo-Pardo, J. Gerl and the GSI groupGSI
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 nuclei
E. Caurier et al., Eur. Phys. J A15 (2002) 145
Fe
Cr
Cr
3
68Ni
K. Langanke et al., Phys. Rev. C67 (2003) 044314

• 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 -gt 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

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In the vicinity of 68Ni

• 67Co
• Collective 1p-2h proton intruder
• First excited ½- state with large quadrupole
  deformation ß 0.25-0.4
• D. Pauwels et al., Phys. Rev. C 78, 041307(R)
  (2009)
• 69Cu
• Measured magnetic moment of 13/2 state
• Considerable proton excitations across the Z28
  proton gap
• Deviate from sphericity
• G. Georgiev et al., J. Phys. G Nucl. Part. Phys.
  28, 2993 (2002)
• 70Zn
• Given as a ?-soft nucleus (Gaudefroy et al.,
  Phys. Rev. C80 (2009) 064313)

• Hunt for deformation with np-nh
• configurations (n6, 8) at higher
• excitation energy

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Shell-model calculations

• Valence space
• 4020Ca20 core
• p f7/2 fp shell
• ? 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
• ß2 0.32
• E 13 MeV
• 6p-6h config
• B(E2)down 190 e²fm4
• Less deformation driving
• E 10 MeV
• 70Zn 6p-6h config
• B(E2)down 695 e²fm4
• Q2 -48 e.fm²
• ß2 0.32
• E 10 MeV
• All configurations are spread over many states
  when configuration mixing is allowed !

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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 h
• Nuclei production rate
• Primary beam 76Ge -gt 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)

105 Hz/wire
104 Hz
Lycca
AGATA
Primary beam (p/s) Intermediate fragment Trans mission S4 rate (p/s) Reaction Final nucleus Production rate (p/s)
7 106 p/s 7331Ga 30 104 fragmentation 6828Ni 0.3
7 106 p/s 7331Ga 30 104 1p-2n knock-out 7030Zn 18
3 107 p/s 7230Zn 42 104 fragmentation 6828Ni 2.5
3 107 p/s 7230Zn 42 104 2n knock-out 7030Zn 35
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Gamma-ray statistics

• S2 geometry
• Full configuration 10TC 5DC -gt 17
• Min. configuration 5TC 3DC -gt 9
• Intermediate fragment 72Zn 1.5 MeV gamma ray
• Experiment duration 7 days

Projectile Nucleus of interest AGATA config. ?-rate (min-1) Total counts singles in 7 days ? ? -rate (min-1) Total counts doubles in 7 days
72Zn 68Ni 2.5 p/s Full 0.19 1900 0.024 244
72Zn 68Ni 2.5 p/s Min 0.10 1000 0.0068 69
72Zn 70Zn 35 p/s Full 2.66 26600 0.34 3400
72Zn 70Zn 35 p/s Min 1.40 14000 0.095 950
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Ni-Zn-Ge
J. Van de Walle et al., Phys. Rev. Lett.99 (2007)
142501
Gaudefroy et al., Phys. Rev. C80 (2009) 064313
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Tensor force

• Attractive between spin-flip orbitals
• Attractive interaction pf5/2-?d5/2
• Relaxed when removing protons from pf5/2 orbital
• Excitation energy of ?s1/2 state apparently
  decreases vs ?d5/2 state

g7/2
s1/2
j1/2
d5/2
g9/2
p1/2
p3/2
j-1/2
f5/2
f7/2
p
?