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1. Isospin Symmetry and Coulomb Effects Towards the Proton Drip-Line RISING Experiment performed October 2003

1. Isospin Symmetry and Coulomb Effects Towards the Proton Drip-Line RISING Experiment performed October 2003 Keele, GSI, Brighton, Lund, Daresbury, Surrey, York, Krakow, Milano, Liverpool, Koln, Bonn, TU Darmstadt Spokesperson: M.A.Bentley (Keele).

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1. Isospin Symmetry and Coulomb Effects Towards the Proton Drip-Line RISING Experiment performed October 2003

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  1. 1. Isospin Symmetry and Coulomb Effects Towards the Proton Drip-Line RISING Experiment performed October 2003 Keele, GSI, Brighton, Lund, Daresbury, Surrey, York, Krakow, Milano, Liverpool, Koln, Bonn, TU Darmstadt Spokesperson: M.A.Bentley (Keele) 2. Effective Charges near 56Ni - Isospin Symmetry in 54Ni - Stopped Beam Proposal Spokesperson: D.Rudolph (Lund), + Lund, Keele, GSI, INFN Legnaro

  2. Isospin Symmetry and Coulomb Effects Towards the Proton Drip-Line • Test the technique of double-fragmentation for studies of excited isobaric analogue states. • First identification of excited states in the Tz= -3/2 nuclei 45Cr and 53Ni identify T=3/2 mirror pairs in f7/2-shell + other proton-rich systems • Isospin symmetry and Coulomb effects towards the proton drip-line - rigorous test of full fp-shell model Nuclei of interest 53Ni 55Ni f7/2-shell 55Co 53Co 53Fe 49Fe 50Fe Complete isobaric multiplets in f7/2-shell… 50Mn 45Cr 50Cr 46Cr T= 1/2 mirror-pairs T= 1 isobaric triplets 45V 46V 42Ti 43Ti 46Ti 45Ti 41Sc 42Sc 43Sc 45Sc Tz= -3/2 (N=Z-3) members of the T=3/2 quadruplet - no excited states known… 42Ca 41Ca

  3. T=1/2 mirror pair 49Mn/49Cr - Coulomb Energy Differences • CED defined as… Alignment of pair of protons in 49Cr (neutrons in 49Mn) Proton alignments in 49Mn (neutrons in 49Cr) C.D. O’Leary, M.A.Bentley et al. Phys. Rev. Lett 79(1997)4349 • T=1 triplet, A=50 mirror pair 50Fe/50Cr (current limit) Experimental CED Full pf-shell model including multipole and monopole Coulomb effects S.M.Lenzi et al PRL 87(2001)122501 CED can only be understood in shell model by including Coulomb effect of different radii of pf-shell proton orbitals, in addition to two-body proton correlations. • T=3/2 mirror-pairs? • Large proton-excess, large difference in Z between mirrors • Larger “one-body” contributions to CED (e.g. orbital radii)? • Towards the drip line - how well does isospin symmetry hold? • Coulomb distortions of proton wave-functions (Thomas-Ehrman)? • Stringent test of shell-model

  4. FRS FRS Intermediate fragment 58Ni Final fragment identification 700 mg cm-29Be secondary target 6.3g cm-29Be primary target Technique: Two-step fragmentation - few-nucleon removal in second step ~170 MeV/A 600 MeV/A • Largest production when intermediate fragment is close to the final fragment of interest (1 or 2 nucleons away) • Expect a few states (yrast and non-yrast?) near in spin to the ground state to be populated. • Performed “mirrored” reactions on each member of the mirror pair with “mirrored” intermediate fragments… to identify populated states. 55Co 53Mn 52Mn 44Sc 58Ni etc. 5×108 s-1 55Ni 53Ni 52Co 44V

  5. N=Z - 3 N=Z - 2 N=Z - 1 Nuclei of interest… Run details… ~ 1 day 55Co intermediate beam (neutron rich mirrors) ~ 4 days 55Ni intermediate beam (proton-rich mirrors) ~ 1 day 54Ni intermediate beam Rates (55Ni): 5108 pps beam, 4105 pps at S2 focus, 5000 pps (55Ni) at S4 Limiting factors: Rate at S2 (maximum rate in scintillator), rate in MUSIC and MW’s (kept at  5 kHz). PREDICTED RELATIVE CROSS-SECTIONS…..

  6. 55Ni Z A/Q • Intermediate fragments identified from time of flight (A/Q) and energy loss in MUSIC (Z) • Almost pure 55Ni beam obtained… • Final fragments only identified by Z (from energy loss) • Mass identification feasible from total energy - but not yet… dE E

  7. 55Co intermediate beam @ 160 MeV/u, b~ 0.45, 1-2103 pps Z-gated spectra (no mass selection), simple Doppler correction G.Hammond (Keele) + J.Grebosz (GSI/Krakow) 411keV ? 6+ - 4+ Fe-gated spectrum, mainly 54Fe - 1p removal sfrag~ 70mb 1131keV 4+ - 2+ 1408keV 2+ - 0+ Cr-gated spectrum, mainly 50Cr - 3p2n removal sfrag~ 20mb 783keV 2+ - 0+ 1098keV 4+ - 2+ 1282keV ? 6+ - 4+

  8. 55Ni intermediate beam @ 163 MeV/u, b~ 0.46, 4-5103 pps Spectra from T.Saitoh (GSI) Doppler corrected with event-by-event particle tracking and b-correction 509keV 2+ - 1+ 4+ - 3+ ? 937keV 1+ - 0+ Co-gated spectrum, mainly N=Z 54Co - 1p removal sfrag~ 20mb * 2+- 0+ Cr-gated spectrum, mainly 50Cr & 49Cr sfrag~ 20mb & 10 mb * = 50Cr, * = 49Cr * * * 4+- 2+ * * 6+- 4+ * 8+- 6+ ? 852keV 2+ - 0+ Fe-gated spectrum, mainly N=Z 52Fe - 2pn removal sfrag~ 30mb 1535keV 4+ - 2+

  9. 55Ni intermediate beam @ 163 MeV/u, b~ 0.46, 4-5103 pps G.Hammond (Keele) Z=27 - gated spectrum - 54Co 509keV 2+ - 1+ 937keV 1+ - 0+ Background from Ni-gated spectrum subtracted (mainly atomic background)

  10. Population of isobaric analogue states in “mirrored” reactions 54Ni 55Ni 55Co 54Co 54Fe 55Co  54Fe - one-proton removal 55Ni  54Ni - one-neutron removal A=54 T=1 isobaric triplet 54Ni lines observed only recently at Euroball - A.Gadea et al (p.c.) From A.Gadea et al. Z=26 gated spectrum, 55Co beam sfrag~5mb Z=28 gated spectrum, 55Ni beam Also, 54Co populated in both reactions by one-particle removal….

  11. Physics outcomes…? • May be difficult to see the T=3/2 nuclei (lower beam intensity, short lifetimes, thick target etc) • BUT - New excited states in at the sfrag <~1mb level - e.g. 52Co (N=Z-2) • Non-yrast states in known proton-rich mirrors ? • Lifetimes from lineshapes (T.Saitoh) • Reaction mechanisms in “mirrored” reactions? • Challenges… • Full tracking algorithms to be implemented • Cleaning up spectra • Position correction for CATE energy - mass resolution (Rady Lozeva, GSI)

  12. Effective Charges near 56Ni - Isospin Symmetry in 54Ni Stopped Beam Proposal Expected Jp = 10+isomer in 54Ni - isobaric analogue state of 10+isomer in 54Fe. Dominant configuration in 54Fe p(f7/2)-2J=6 n(fp)J=4 Mirrored configuration in 54Ni n(f7/2)-2J=6 p(fp)J=4 States in 54Ni known up to the (f7/2)-2Jp = 6+band termination A.Gadea (LNL) et al G.Hammond + RISING et al.

  13. experiment Jp = 10+ isomer in 54Fe - shell model predictions… • Effective charges crucial ingredient in SM - depend strongly on model space • Proposal: identify the transitions from the expected Jp = 10+ isomer in 54Ni - measurement of branching ratio and lifetime • Thus, gives (a) effective charges for protons and neutronsand (b) stringent test of the (presumed) isobaric analogue wave functions.

  14. Predicted lifetime of Jp = 10+ isomer in 54Ni… • Prompt gammas (up to 6+) observed in 54Ni at Euroball (2n reaction) - but low beam energy/entry spin • NOT seen at Gammasphere with higher spin/energy entry point (from a2n reaction) • Implies lifetime of Jp = 10+ isomer at least 0.5ms.

  15. Thus, ideally suited to RISING (t > 0.5ms) • 54Ni beam (from 58Ni) selected cleanly by FRS (already achieved) • “Worst case” (t = 0.5ms, br=4%) achievable in ~ few days beam time - (5% isomeric ratio) • Question - is 58Ni too near to 54Ni? Use 63Cu beam?

  16. Thanks to… GSI RISING team + Helmholtz-Ins. Bonn Uni. Brighton CLRC Daresbury TU Darmstadt Uni. Lund INFN Milano Uni. Koln IFJ Krakow Uni. Liverpool Uni. Surrey Uni. York

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