1. Isospin Symmetry and Coulomb Effects Towards the Proton Drip-Line

RISING Experiment performed October 2003Keele, 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

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

50Fe

50Mn

50Cr

46V

46Cr

46Ti

53Co

49Fe

45Cr

53Fe

55Ni

55Co

45V

45Ti43Ti

43Sc

41Ca

41Sc

53Ni

45Sc

42Ti

42Sc

42Ca

f7/2-shell

Complete isobaric multiplets in f7/2-shell…

T= 1/2 mirror-pairs

T= 1 isobaric triplets

Tz= -3/2 (N=Z-3) members of the T=3/2 quadruplet - no excited states known…

Nuclei of interest

-40-20

020406080

100

3 7 11 15 19 23 27 312J

CE

D (k

eV)

Alignment of pair of protons in 49Cr (neutrons in 49Mn)

Proton alignments in 49Mn (neutrons in 49Cr)

• T=1/2 mirror pair 49Mn/49Cr - 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 50Fe/50Cr (current limit)

Experimental CED

Full pf-shell modelincluding 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)122501

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

veTveT zzJExJExJCED

58Ni

FRS FRS

6.3g cm-2 9Be primary target

700 mg cm-2 9Be 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.

5×108 s-155Ni

55Co58Ni

53Ni

53Mn

52Co

52Mn

44V

44Sc

etc.

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): 5108 pps beam, 4105 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…..

N=Z - 3

N=Z - 2

N=Z - 1

Nuclei of interest…

Z

A/Q

55Ni

E

dE

• 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…

55Co intermediate beam @ 160 MeV/u, ~ 0.45, 1-2103 pps

Z-gated spectra (no mass selection), simple Doppler correction

G.Hammond (Keele) + J.Grebosz (GSI/Krakow)

Fe-gated spectrum, mainly 54Fe - 1p removal

frag~ 70mb

Cr-gated spectrum, mainly 50Cr - 3p2n removal

frag~ 20mb

1408keV 2+ - 0+

1131keV 4+ - 2+

411keV ? 6+ - 4+

783keV 2+ - 0+

1098keV 4+ - 2+

1282keV ? 6+ - 4+

55Ni intermediate beam @ 163 MeV/u, ~ 0.46, 4-5103 ppsSpectra from T.Saitoh (GSI)Doppler corrected with event-by-event particle tracking and -correction

Co-gated spectrum, mainly N=Z 54Co - 1p removal

frag~ 20mb

937keV 1+ - 0+

509keV 2+ - 1+

4+ - 3+ ?

Cr-gated spectrum, mainly 50Cr & 49Cr

frag~ 20mb & 10 mb

* = 50Cr, * = 49Cr

**

* 2+- 0+

* * 4+- 2+

* 6+- 4+

* 8+- 6+ ?

Fe-gated spectrum, mainly N=Z 52Fe - 2pn removal

frag~ 30mb

852keV 2+ - 0+

1535keV 4+ - 2+

55Ni intermediate beam @ 163 MeV/u, ~ 0.46, 4-5103 pps

Z=27 - gated spectrum - 54Co509keV 2+ - 1+

937keV 1+ - 0+

Background from Ni-gated spectrum subtracted (mainly atomic background)

G.Hammond (Keele)

Population of isobaric analogue states in “mirrored” reactions55Co 54Fe - one-proton removal55Ni 54Ni - one-neutron removal

55Co

55Ni

54Fe

54Ni

54Co

A=54 T=1 isobaric triplet54Ni lines observed only recently at Euroball - A.Gadea et al (p.c.)

Z=28 gated spectrum, 55Ni beam

Z=26 gated spectrum, 55Co beam

From A.Gadea et al.

frag~5mb

Also, 54Co 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. 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)

Effective Charges near 56Ni - Isospin Symmetry in 54Ni Stopped Beam Proposal

Expected J = 10+ isomer in 54Ni - isobaric analogue state of 10+ isomer in 54Fe.

Dominant configuration in 54Fe (f7/2)-2J=6 (fp)J=4

Mirrored configuration in 54Ni (f7/2)-2J=6 (fp)J=4

States in 54Ni known up to the (f7/2)-2 J = 6+ band termination

A.Gadea (LNL) et al

G.Hammond + RISING et al.

J = 10+ isomer in 54Fe - 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 54Ni - 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 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 2n reaction)

• Implies lifetime of J = 10+ isomer at least 0.5s.

• Thus, ideally suited to RISING ( > 0.5s)

• 54Ni beam (from 58Ni) selected cleanly by FRS (already achieved)

• “Worst case” ( = 0.5s, br=4%) achievable in ~ few days beam time - (5% isomeric ratio)

• Question - is 58Ni too near to 54Ni? Use 63Cu 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