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Lifetime measurements around the doubly-magic 48 Ca nucleus

Lifetime measurements around the doubly-magic 48 Ca nucleus. Jo s e Javier Valiente Dob ó n (INFN-LNL, Italy). Overview. Lifetime measurements of neutron-rich nuclei via MNT: RDDS + CLARA +PRISMA Results for N=30 isotones ( 50 Ca, 51 Sc) Result for the N=28 46 Ar Summary.

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Lifetime measurements around the doubly-magic 48 Ca nucleus

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  1. Lifetime measurements around the doubly-magic 48Ca nucleus Jose Javier Valiente Dobón (INFN-LNL, Italy)

  2. 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

  3. Grazing reactions Tool to populate neutron-rich nuclei Fission 238U Grazing Target-like LAB. Grazing Beam-like Target Beam Substantial kinetic energy damping and mass exchange while retaining partial memory and entrance-channel masses and charges 82Se + 238U, E=505 MeV G.de Angelis, G.Duchêne

  4. The CLARA-PRISMA setup Laboratori Nazionali di Legnaro (INFN), Italy PRISMA • Gamma spectrometer • CLARA • Magnetic spectrometer • PRISMA CLARA

  5. The CLARA spectrometer • 23 Euroball Clover detectors with anti-Compton (Eff. ~ 3.0 %) • FWHM = 0.9% (for β=10%)  spectrum CLARA spectrometer

  6. The PRISMA spectrometer Large-acceptance magnetic 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 PRISMA spectrometer

  7. Target-Degrader setup Pictures of the fixed Plunger Target Ta:1mg/cm2208Pb:1mg/cm2 Plunger setup Degrader natMg: 4mg/cm2 Beam Distances set by metallic rings

  8. Experimental setup Recoil Distance Doppler Shift method (RDDS) Eγ Eγ’ CLARA Placed at the θgrazing for BLF Eγ’ Eγ Eγ’: Doppler corrected PRISMA β’≈8.0% natMg Beam 48Ca β≈10.0% Good Mass Resolution Ebeam=310MeV d Degrader Target 208Pb Multi-nucleon transfer reactions

  9. Around the doubly-magic 48Ca The N=30 isotones The Z=18 isotopes

  10. Nuclei in the fp shell The case of 50Ca-51Sc and 51Mn-51Fe 51Fe N=Z 51Mn 51Sc 50Ca

  11. Experimental RDDS spectra Rection: 48Ca onto 208Pb at 310 MeV Gamma spectra of the 2+ and 11/2- in 50Ca and 51Sc (mass gate in PRISMA) Iu Is Mass spectrum from PRISMA

  12. Lifetimes of first excited states Velocity PRISMA CLARA ring The velocity required is the velocity before the degrader. PRISMA measures the velocity after the degrader

  13. B(E2) and Eff. charges of N=30 Shell-model calculations in the full fp shell 40Ca core (KB3G & GXPF1A): • 50Ca wave function of the 2+ → vp23/2 • 51Sc wave function of the 11/2- → vp23/2, πf7/2 E2+ B(E2) Calcium systematics E and B(E2) Experimental and theoretical effective charges.

  14. Effective charge Neutron deficient A=51 mirror nuclei 51Fe and 51Mn ISOSCALAR + ISOVECTOR: (eeff)pE2=1.15e (eeff)nE2=0.8e

  15. Ductu Naturae Full fp shell with a 40Ca core. (eeff)pE2=1.15e (eeff)nE2=0.80e 51Fe N=Z 51Mn (eeff)pE2=1.50e (eeff)nE2=0.50e 51Sc 50Ca A HO potential and separable (IS and IV) QQ interactions → Effective charges are constant for a given core and valence space.

  16. The N=28 isotope: 46Ar • Full GEANT4 simulations : • CLARA • PRISMA • Realistic velocity distributions • Energy loss degrader τ=0.8(0.3)ps • Simulations performed in order to deduce the lifetime of the 2+ state in 46Ar

  17. 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.

  18. AGATA + PRISMA: Lifetimes CLARA vs. AGATA Lifetime τ=100ps Degrader natMg 4 mg/cm2 AGATA CLARA

  19. Summary • 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

  20. Collaborators

  21. Harmonic Oscillator & Woods-Saxon Spherical Harmonic Oscillator potential ‹r2›(p3/2)=‹r2›(f7/2) Spherical Woods-Saxon potential ‹r2›(p3/2)≈ 1.2‹r2›(f7/2) ↓ (eeff)nE2=0.42e

  22. Effective charges As a reference the effective charges eeff associated to a free nucleon: Proton (eeff)p=1.0e (eeff)n=0.0e Neutron The E2-polarization effect gives rise to an effective charge eeff associated with the quadrupole processes: Proton Neutron A HO potential and separable (IS and IV) QQ interactions → Effective charges are constant for a given core and valence space.

  23. The IS+IV effective charges Possible explanation for the staggering in B(E2) for Ti N=32 N=28 N=30 A. Poves et al., Phys. Rev. C 72, 047302 (2005)

  24. p1/2 fp f5/2 p3/2 f7/2 40Ca CORE GQR (IS) GQR (IV) What are effective charges. Full fp shell with a 40Ca core. For a pure configuration: B(E2: ν(p3/2)2 ) ~ (eνeff)2 ‹r2›2 (p3/2) 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. Nuclear Structure, Bohr and Mottelson.

  25. 20 20 20 20 N=30 isotones Neutron-rich 50Ca and 51Sc isotopes Well known from multi-nucleon and deep-inelastic reactions (thin and thick target). R. Broda et al., Acta Phys. Pol. B36 (2005) 1343.

  26. 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%)  spectrum CLARA spectrometer

  27. The PRISMA spectrometer Large-acceptance magnetic 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 PRISMA spectrometer

  28. Target-Degrader setup Pictures of the fixed Plunger Target Ta:1mg/cm2208Pb:1mg/cm2 Plunger setup Degrader natMg: 4mg/cm2 Beam Distances set by metallic rings

  29. Control of the feeding Total Kinetic Energy Loss 2+→0+ 4+→2+ C1 4+ τ≈9.02±2.16 ps C2 2+ 2+→0+ 0+ 46Ca τ≈5.50±2.17 ps TKEL = -Qvalue Coulex: τ=5.24±0.54 ps M. Bini et al., Nuovo Cimento Lett. 5 913 (1972).

  30. Future at LNL: AGATA D. & PRISMA CLARA does not exist anymore ... • Lifetime measurements • AGATA 0o – 45° • εAD≈ 6% • Cologne Plunger • γ-γ coincidences PRISMA Degrader Target Beam

  31. 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.

  32. Energies and B(E2) values Indication of shell gaps B(E2) values Energy Energies and B(E2) values are complementary to study in detail shell evolution. N=28 N=32 54Ca 52Ca Energy 50Ca KB3G: A. Poves, et al., Nucl. Phys. A (2001). GXPF1A: M. Honma et al., Phys. Rev. C (2002);Eur. Phys. J. A (2004). 34

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