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Isomeric beams at CARIBU

Isomeric beams at CARIBU. ATLAS Users Meeting 2014. May 15, 2014. Ching-Yen Wu. Outline. Motivation and experimental approach Initial focus A case study in details Summary. Physics motivation. Evolution of nuclear quadrupole collectivity

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Isomeric beams at CARIBU

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  1. Isomeric beams at CARIBU ATLAS Users Meeting 2014 • May 15, 2014 • Ching-Yen Wu

  2. Outline • Motivation and experimental approach • Initial focus • A case study in details • Summary

  3. Physics motivation • Evolution of nuclear quadrupole collectivity • Shape transition and shape coexistence in neutron-rich nuclei with A ~ 100 • Nuclear structure sensitive to the occupancy level of the h11/2 neutron and g9/2 proton orbitals • Manifestations are (1) the sudden onset of quadrupole deformation in Sr and Zr isotopes, (2) the emerging  degree of freedom in Mo – Ru region, and (3) the predicted triaxial shape transition from prolate to oblate in Ru – Pd region • Ideal testing ground for various theoretical models, including the nuclear density functional theory • Milestone NS9 for 2018 defined by NSAC Subcommittee on Performance Measures

  4. Experimental approach • Probe the shape transition and shape coexistence in nuclei by measuring their electromagnetic properties using the sub-barrier Coulomb excitation method • Extract the transition and static matrix elements for the -ray transitions measuredby(Digital) Gamasphere or GRETINA /CHICO2

  5. Initial focus • Shape transition and shape coexistence in 96,98Y • Both have long-lived isomers with the same decay mode and similar lifetime of those for the ground states but different spin and shape • The ground states have spin 0– and the characteristics of spherical shape • 96mY (T1/2 = 9.6 s) has spin 8+ with Eex = 1130 keV and intrinsic Q0 = – 1.40 b (Laser spectroscopy) • 98mY (T1/2 = 2.0 s) has spin (4 or 5) with Eex = 410 keV and intrinsic Q0 = 3.12 b (Laser spectroscopy)

  6. Estimated cross sections and counts • K = 5+ for 98mY (T1/2 = 2.0 s) at Eex = 410 keV • Intrinsic Q0 = 3.12 b • 420 MeV98mY on 208Pb of 1 mg/cm2 • 7 days of beam-on-target with intensity ~ 2,000 pps • Integrate the scattered angle from 40o to 70o • 10%  efficiency

  7. Summary • Provide the precision measured electromagnetic properties for neutron-rich nuclei with A ~ 100 to test and improve the predictability of nuclear models such as nuclear density functional theory • An example is given to illustrate the study of the electromagnetic properties for the available isomeric beams at CARIBU • Quadrupole collectivity can be studied for the excited states with spin up to 10 for the well-deformed 98mY • The transition and static matrix elements can be determined for transitions with the cross section as low as 10 mb within a reasonable time frame

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