lifetime measurements around the doubly-magic 48 ca nucleus

Jose Javier Valiente Dobón (INFN-LNL, Italy)

Lifetime measurements around the doubly-magic 48Ca nucleus

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

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

PRISMA

The CLARA-PRISMA setup

• Gamma spectrometer

CLARA

• Magnetic spectrometer

PRISMA

CLARA

Laboratori Nazionali di Legnaro (INFN), Italy

The CLARA spectrometer

• 23 Euroball Clover detectors with anti-Compton (Eff. ~ 3.0 %)

• FWHM = 0.9% (for β=10%)

spectrumCLARA spectrometer

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

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

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

Around the doubly-magic 48Ca

The Z=18 isotopes

The N=30 isotones

Nuclei in the fp shellThe case of 50Ca-51Sc and 51Mn-51Fe

N=Z

51Fe51Mn

50Ca

51Sc

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

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

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):

Effective charge

ISOSCALAR + ISOVECTOR:

(eeff)pE2=1.15e

(eeff)nE2=0.8e

Neutron deficient A=51 mirror nuclei 51Fe and 51Mn

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.

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

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.

AGATA + PRISMA: LifetimesCLARA vs. AGATA

CLARA

AGATA

Lifetime τ=100ps Degrader natMg 4 mg/cm2

• 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

Collaborators

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

↓

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.

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

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)

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

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

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

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

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

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 ...

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.

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