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 56 Ni - Isospin Symmetry in 54 Ni - Stopped Beam Proposal Spokesperson: D.Rudolph (Lund), + Lund, Keele, GSI, INFN Legnaro

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 T z = -3/2 nuclei 45 Cr and 53 Ni identify T=3/2 mirror pairs in f 7/2 -shell + other proton-rich systems Isospin symmetry and Coulomb effects towards the proton drip-line - rigorous test of full fp-shell model 50 Fe 50 Mn 50 Cr 46 V 46 Cr 46 Ti 53 Co 49 Fe 45 Cr 53 Fe 55 Ni 55 Co 45 V 45 Ti 43 Ti 43 Sc 41 Ca 41 Sc 53 Ni 45 Sc 42 Ti 42 Sc 42 Ca f 7/2 -shell Complete isobaric multiplets in f 7/2 -shell… T= 1/2 mirror-pairs T= 1 isobaric triplets T z = -3/2 (N=Z-3) members of the T=3/2 quadruplet - no excited states known… Nuclei of interest

Alignment of pair of protons in 49 Cr (neutrons in 49 Mn) Proton alignments in 49 Mn (neutrons in 49 Cr) T=1/2 mirror pair 49 Mn/ 49 Cr - Coulomb Energy Differences CED defined as… C.D. O’Leary, M.A.Bentley et al. Phys. Rev. Lett 79(1997)4349 T=1 triplet, A=50 mirror pair 50 Fe/ 50 Cr (current limit) Experimental CED Full pf-shell model including multipole and monopole Coulomb effects 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. S.M.Lenzi et al PRL 87(2001) 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

58 Ni FRS 6.3g cm -2 9 Be primary target 700 mg cm -2 9 Be secondary target Intermediate fragment Final fragment identification 600 MeV/A ~170 MeV/A Technique: Two-step fragmentation - few-nucleon removal in second step 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. 5×10 8 s Ni 55 Co 58 Ni 53 Ni 53 Mn 52 Co 52 Mn 44 V 44 Sc etc.

Run details… ~ 1 day 55 Co intermediate beam (neutron rich mirrors) ~ 4 days 55 Ni intermediate beam (proton-rich mirrors) ~ 1 day 54 Ni intermediate beam Rates ( 55 Ni): 5  10 8 pps beam, 4  10 5 pps at S2 focus, 5000 pps ( 55 Ni) 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….. N=Z - 3 N=Z - 2 N=Z - 1 Nuclei of interest…

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

55 Co intermediate 160 MeV/u,  ~ 0.45, 1-2  10 3 pps Z-gated spectra (no mass selection), simple Doppler correction G.Hammond (Keele) + J.Grebosz (GSI/Krakow) Fe-gated spectrum, mainly 54 Fe - 1p removal  frag ~ 70mb Cr-gated spectrum, mainly 50 Cr - 3p2n removal  frag ~ 20mb 1408keV keV keV ? keV keV keV ?

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

55 Ni intermediate 163 MeV/u,  ~ 0.46, 4-5  10 3 pps Z=27 - gated spectrum - 54 Co 509keV keV Background from Ni-gated spectrum subtracted (mainly atomic background) G.Hammond (Keele)

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

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  frag <~  1mb level - e.g. 52 Co (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)

Effective Charges near 56 Ni - Isospin Symmetry in 54 Ni Stopped Beam Proposal Expected J  = 10 + isomer in 54 Ni - isobaric analogue state of 10 + isomer in 54 Fe. Dominant configuration in 54 Fe  (f 7/2 ) -2 J=6  (fp) J=4 Mirrored configuration in 54 Ni (f 7/2 ) -2 J=6   (fp) J=4 States in 54 Ni known up to the (f 7/2 ) -2 J  = 6 + band termination A.Gadea (LNL) et al G.Hammond + RISING et al.

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

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

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

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