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Jose Javier Valiente Dobón (INFN-LNL, Italy)
Lifetime measurements around the doubly-magic 48Ca nucleus
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Overview
•Lifetime measurements of neutron-rich nuclei via MNT: RDDS + CLARA +PRISMA
•Results for N=30 isotones (50Ca, 51Sc)
•Result for the N=28 46Ar
•Summary
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Grazing reactionsTool to populate neutron-rich nuclei
Target
Beam
Grazing Target-like
Grazing Beam-like
LAB.
Substantial kinetic energy damping and mass exchange while retaining partial memory and
entrance-channel masses and charges
82Se + 238U, E=505 MeV
Fission 238U
G.de Angelis, G.Duchêne
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PRISMA
The CLARA-PRISMA setup
• Gamma spectrometer
CLARA
• Magnetic spectrometer
PRISMA
CLARA
Laboratori Nazionali di Legnaro (INFN), Italy
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The CLARA spectrometer
• 23 Euroball Clover detectors with anti-Compton (Eff. ~ 3.0 %)
• FWHM = 0.9% (for β=10%)
spectrumCLARA spectrometer
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The PRISMA spectrometer
• Formed by 1 Quadrupole, 1 Dipole and detectors (MCP, MWPPAC, IC) to track the ions.
• ΔΩ = 80 msr, ΔZ/Z 1/60, ΔA/A 1/190, Bρ = 1.2 T.m
• Identifies nuclei produced in the reaction (A,Z,β) event by event
I C
MWPPAC
I C
MWPPAC
PRISMA spectrometer
Large-acceptance magnetic spectrometer
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Target-Degrader setup
Degrader
Target
Beam
Plunger setup
Ta:1mg/cm2 208Pb:1mg/cm2
natMg: 4mg/cm2
Pictures of the fixed Plunger
Distances set by metallic rings
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Experimental setup
Beam 48Ca
208Pb
natMg
PRISMA
β≈10.0%
β’≈8.0%
Ebeam=310MeVdDegrader Target
Eγ’ Eγ
CLARA
Recoil Distance Doppler Shift method (RDDS)
Eγ Eγ’
Eγ’: Doppler corrected
Good Mass Resolution
Multi-nucleon transfer reactions
Placed at the θgrazing for BLF
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Around the doubly-magic 48Ca
The Z=18 isotopes
The N=30 isotones
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Nuclei in the fp shellThe case of 50Ca-51Sc and 51Mn-51Fe
N=Z
51Fe51Mn
50Ca
51Sc
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Experimental RDDS spectra
IsIu
Gamma spectra of the 2+ and 11/2- in 50Ca and 51Sc (mass gate in PRISMA)
Mass spectrum from PRISMA
Rection: 48Ca onto 208Pb at 310 MeV
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Lifetimes of first excited states
The velocity required is the velocity before the degrader. PRISMA measures the velocity after the
degrader
cos)'('
' E
EE
Velocity PRISMA
CLARA ring
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B(E2) and Eff. charges of N=30
Calcium systematics E and B(E2) Experimental and theoretical effective charges.
E2+
B(E2)
•50Ca wave function of the 2+ → vp23/2
•51Sc wave function of the 11/2- → vp23/2, πf7/2
Shell-model calculations in the full fp shell 40Ca core (KB3G & GXPF1A):
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Effective charge
ISOSCALAR + ISOVECTOR:
(eeff)pE2=1.15e
(eeff)nE2=0.8e
Neutron deficient A=51 mirror nuclei 51Fe and 51Mn
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Ductu Naturae
N=Z
51Fe51Mn
50Ca
51Sc
(eeff)pE2=1.15e
(eeff)nE2=0.80e
(eeff)pE2=1.50e
(eeff)nE2=0.50e
Full fp shell with a 40Ca core.
A HO potential and separable (IS and IV) QQ interactions → Effective charges are constant for a given core and valence space.
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The N=28 isotope: 46Ar
•Simulations performed in order to deduce the lifetime of the 2+ state in 46Ar
Full GEANT4 simulations :
•CLARA
•PRISMA
•Realistic velocity distributions
•Energy loss degrader
τ=0.8(0.3)ps
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B(E2) value of 46Ar
•Collectivity arises from proton (sd) neutron (fp) interaction
•Increased collectivity with respect to 44Ar
A. Gade et al., Phys. Rev. C68 (2003) 014302., H. Scheit et al., Phys. Rev. Lett 77 (1996) 3967.
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AGATA + PRISMA: LifetimesCLARA vs. AGATA
CLARA
AGATA
Lifetime τ=100ps Degrader natMg 4 mg/cm2
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• Novel method that combines the traditional RDDS method with the CLARA-PRISMA spectrometers, allowing to measure lifetimes of neutron-rich nuclei.
• Complementarity of this method with Coulex with radioactivy beams
• Results on the lifetime of the first excited states in the N=30 isotones 50Ca and 51Sc. Determination of the effective charges in the fp shell.
• Indication of an orbital dependence of the effective charges in the fp shell.
• Need of more experimental data of selected nuclei to fully understand the question.
• Measured lifetime of 46Ar, increased collectivity.
• Future: AGATA at LNL
Summary
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Collaborators
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Harmonic Oscillator & Woods-Saxon
Spherical Woods-Saxon potential
Spherical Harmonic Oscillator potential
‹r2› (p3/2)= ‹r2›
(f7/2)
‹r2› (p3/2)≈ 1.2 ‹r2›
(f7/2)
(eeff)nE2=0.42e
↓
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Effective charges
22
22
)()(
)()(
EpolneutronEeff
EpolprotonEeff
ee
eee
The E2-polarization effect gives rise to an effective charge eeff
associated with the quadrupole processes:
Proton
Neutron
As a reference the effective charges eeff associated to a free nucleon:
(eeff)p=1.0e
(eeff)n=0.0e
Proton
Neutron
A HO potential and separable (IS and IV) QQ interactions → Effective charges are constant for a given core and valence space.
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The IS+IV effective charges
A. Poves et al., Phys. Rev. C 72, 047302 (2005)
Possible explanation for the staggering in B(E2) for Ti
N=28
N=30
N=32
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What are effective charges.
Effective charges take into account the core polarization, that can be understood in terms of the coupling between the particles and the
collective oscillations associated with deformations of the core.
GQR (IS) GQR (IV)
f7/2
p3/2
p1/2
f5/2fp
40CaCORE
Full fp shell with a 40Ca core.
Nuclear Structure, Bohr and Mottelson.
For a pure configuration: B(E2: ν(p3/2)2 ) ~ (eνeff)2 ‹r2›2
(p3/2)
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N=30 isotones
Well known from multi-nucleon and deep-inelastic reactions (thin and thick target).
R. B
roda et al., Acta P
hys. Pol. B
36 (2005) 1343.
Neutron-rich 50Ca and 51Sc isotopes
20 20
20 20
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The CLARA spectrometer
• 23 Euroball Clover detectors with anti-Compton (Eff. ~ 3.0 %)
• Not used detectors around 90o→ Doppler shift ≈ 0 (Eff. ~ 1.2 %)
• FWHM = 0.6% (for β=10%)
spectrumCLARA spectrometer
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The PRISMA spectrometer
• Formed by 1 Quadrupole, 1 Dipole and detectors (MCP, MWPPAC, IC) to track the ions.
• ΔΩ = 80 msr, ΔZ/Z 1/60, ΔA/A 1/190, Bρ = 1.2 T.m
• Identifies nuclei produced in the reaction (A,Z,β) event by event
I C
MWPPAC
I C
MWPPAC
PRISMA spectrometer
Large-acceptance magnetic spectrometer
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Target-Degrader setup
Degrader
Target
Beam
Plunger setup
Ta:1mg/cm2 208Pb:1mg/cm2
natMg: 4mg/cm2
Pictures of the fixed Plunger
Distances set by metallic rings
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Control of the feeding
4+
0+
2+
C1
C2
46Ca
Total Kinetic Energy Loss
TKEL = -Qvalue
2+→0+4+→2+
2+→0+
τ≈9.02±2.16 ps
τ≈5.50±2.17 ps
M. Bini et al., Nuovo Cimento Lett. 5 913 (1972).Coulex: τ= 5.24±0.54 ps
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Future at LNL: AGATA D. & PRISMA
Degrader
Target
Be
am
PRISMA
Lifetime measurements
•AGATA 0o – 45°
•εAD ≈ 6%
•Cologne Plunger
•γ-γ coincidences
CLARA does not exist anymore ...
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Effective charges & B(E2) values
The relation between the effective charges and the B(E2) value for a pure configuration can be given:
B(E2: ν(p3/2)2 ) ~ (eνeff)2 ‹r2›2
(p3/2)
If we consider a Harmonic Oscillator potential, the ‹r2› is the same for any give orbital of the same quantum number N.
Therefore in our valence space: ‹r2› (p3/2)= ‹r2›
(f7/2)
If we consider a simple model with a HO potential and separable (IS and IV) QQ interactions → The effective charges are the same for a given core and valence space for all nuclei.
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Energies and B(E2) valuesIndication of shell gaps
B(E2) values Energy
N=28
N=32
Energies and B(E2) values are complementary to study in detail shell evolution.
34
KB3G: A. Poves, et al., Nucl. Phys. A (2001).
GXPF1A: M. Honma et al., Phys. Rev. C (2002); Eur. Phys. J. A (2004).
50Ca
52Ca
54Ca
Ene
rgy