1. New Shell Structure at N>>Z Lifetime measurement of the first excited 2+ state in 52Ti
H.J. Wollersheim, P. Doornenbal, J. Gerl
Gesellschaft für Schwerionenforschung, P.O. Box , D Darmstadt, Germany
A. Dewald, K.O. Zell
Institut für Kernphysik, Universität Köln, Zülpicherstrasse 77, D Köln, Germany
R.K. Bhowmik, R. Kumar, S. Muralithar, R.P. Singh
Nuclear Science Centre, P.O. Box 10502, New Delhi , India
S.K. Mandal, Ranjeet
Department of Physics & Astrophysics, University of Delhi, New Delhi , India
The Z~20, N~34region
It is known experimentally that the neutron νf5/2 orbit from 57Ni towards 49Ca undergoes
a large monopole shift due to the reduced binding with increasing removal of the proton f7/2
S=0 spin-orbit partners. Beyond N=28 this opens a gap between the ν(p3/2,p1/2) and νf5/2
orbits, which might be subject to change depending on the 2p1/2 position, as this also forms a
S=0 pair with π1f7/2 but with less radial overlap.
In the figure experimental signatures for shell structure are shown:
the two-nucleon separation energy differences δ2n/δ2p,
the 2+ excitation energies E(2+),
the B(E2;2+ →0+) values
In the Ca isotopes beyond N=28 a possible (sub)shell closure at N=32,34 seems to develop in E(2+).
The Cr isotopes show a maximum in E(2+) at N=32.
On the other hand within the N=34 isotones E(2+) is increasing from Fe
to Cr in contrast to the expected trend towards midshell, which supports a N=34 closure.
Besides masses, which due to short half lives are difficult to measure, obviously E(2+) and B(E2)
values for 50-54Ca are missing for a proof of the concept. Similarly a study of the N=30-34
isotones of Cr and Ti would reveal such a change in shell structure.
The shell behaviour in the N~40-50 region is dominated by the monopole strength of the πf5/2 νg9/2
and πf7/2 νf5/2 pairs of nucleons, which is known from experiment. At N=40 68Ni as an
isolated nucleus exhibits doubly-magic features, which rapidly disappear when adding protons
into πf5/2 or removing them from πf7/2 as in both cases the gap between νg9/2 and νf5/2 is
closed by increased νg9/2 and decreased νf5/2 binding, respectively. It is an interesting question
whether this affects the N=50 shell at 78Ni, too, where the πf5/2 orbit is empty, which shifts
νg9/2 towards νd5/2.

2. New Shell Structure at N>>Z Experiments with N=28-34 Nuclei
Collaboration: Cologne, GSI, NSC, Delhi
Spokesperson: H.J. Wollersheim, R.K. Bhowmik
f 5/2
The Z~20, N~34region
It is known experimentally that the neutron νf5/2 orbit from 57Ni towards 49Ca undergoes
a large monopole shift due to the reduced binding with increasing removal of the proton f7/2
S=0 spin-orbit partners. Beyond N=28 this opens a gap between the ν(p3/2,p1/2) and νf5/2
orbits, which might be subject to change depending on the 2p1/2 position, as this also forms a
S=0 pair with π1f7/2 but with less radial overlap.
In the figure experimental signatures for shell structure are shown:
the two-nucleon separation energy differences δ2n/δ2p,
the 2+ excitation energies E(2+),
the B(E2;2+ →0+) values
In the Ca isotopes beyond N=28 a possible (sub)shell closure at N=32,34 seems to develop in E(2+).
The Cr isotopes show a maximum in E(2+) at N=32.
On the other hand within the N=34 isotones E(2+) is increasing from Fe
to Cr in contrast to the expected trend towards midshell, which supports a N=34 closure.
Besides masses, which due to short half lives are difficult to measure, obviously E(2+) and B(E2)
values for 50-54Ca are missing for a proof of the concept. Similarly a study of the N=30-34
isotones of Cr and Ti would reveal such a change in shell structure.
The shell behaviour in the N~40-50 region is dominated by the monopole strength of the πf5/2 νg9/2
and πf7/2 νf5/2 pairs of nucleons, which is known from experiment. At N=40 68Ni as an
isolated nucleus exhibits doubly-magic features, which rapidly disappear when adding protons
into πf5/2 or removing them from πf7/2 as in both cases the gap between νg9/2 and νf5/2 is
closed by increased νg9/2 and decreased νf5/2 binding, respectively. It is an interesting question
whether this affects the N=50 shell at 78Ni, too, where the πf5/2 orbit is empty, which shifts
νg9/2 towards νd5/2.
Neutron-rich Ca-, Ti-, Cr-Isotopes
protons are removed from the pf7/2 shell
weaker pf7/2 –nf5/2 monopole pairing
interactions
nf5/2 moves up in energy
possible shell gaps at N=32 and N=34?

3. New Shell Structure at N>>Z Experiments with N=28-34 Nuclei
Comparison: 2+ systematics
and shell model calculations
N=32 for Z24 (Cr)
N=32, N=34 for Z  22 (Ti)
Transition matrix elements?
The Z~20, N~34region
It is known experimentally that the neutron νf5/2 orbit from 57Ni towards 49Ca undergoes
a large monopole shift due to the reduced binding with increasing removal of the proton f7/2
S=0 spin-orbit partners. Beyond N=28 this opens a gap between the ν(p3/2,p1/2) and νf5/2
orbits, which might be subject to change depending on the 2p1/2 position, as this also forms a
S=0 pair with π1f7/2 but with less radial overlap.
In the figure experimental signatures for shell structure are shown:
the two-nucleon separation energy differences δ2n/δ2p,
the 2+ excitation energies E(2+),
the B(E2;2+ →0+) values
In the Ca isotopes beyond N=28 a possible (sub)shell closure at N=32,34 seems to develop in E(2+).
The Cr isotopes show a maximum in E(2+) at N=32.
On the other hand within the N=34 isotones E(2+) is increasing from Fe
to Cr in contrast to the expected trend towards midshell, which supports a N=34 closure.
Besides masses, which due to short half lives are difficult to measure, obviously E(2+) and B(E2)
values for 50-54Ca are missing for a proof of the concept. Similarly a study of the N=30-34
isotones of Cr and Ti would reveal such a change in shell structure.
The shell behaviour in the N~40-50 region is dominated by the monopole strength of the πf5/2 νg9/2
and πf7/2 νf5/2 pairs of nucleons, which is known from experiment. At N=40 68Ni as an
isolated nucleus exhibits doubly-magic features, which rapidly disappear when adding protons
into πf5/2 or removing them from πf7/2 as in both cases the gap between νg9/2 and νf5/2 is
closed by increased νg9/2 and decreased νf5/2 binding, respectively. It is an interesting question
whether this affects the N=50 shell at 78Ni, too, where the πf5/2 orbit is empty, which shifts
νg9/2 towards νd5/2.
Theory:
GXPF1, GXPF1A
M.Honma et al, Phys. Rev. C65(2002)061301
KB3G
E.Caurier et al, Eur.Phys.J. A 15, 145 (2002)

4. Rare ISotope INvestigation at GSI Spectroscopy at relativistic energies
Fragment Separator FRS provides secondary radioactive ion beams:
fragmentation and fission of primary beams
high secondary beam energies: 100 – 500 MeV/u
fully stripped ions
FRS
RISING

5. RISING experimental setup
Ge Cluster detectors
Target chamber
CATE
beam
BaF2 HECTOR detectors

6. New Shell Structure at N>>Z Relativistic Coulex in N=28-34 Nuclei
B(E2) values for 56,58Cr
Eg [keV]
Nions Ig
eff.corr..
This work B(E2) [Wu]
Prev. work B(E2) [Wu]
54Cr
835
3.0·107
21300
Normali- sation
14.6(6)
56Cr
1006
1.5·107
6500
8.5 (2.5)
---
58Cr
880
1.0·107
7800
14.1 (3.9)
PRELIMINARY
RISING results from A. Bürger, Bonn

7. Tracking: scattering angle determination
Doppler correction of measured g-rays
 impact parameter measurement
exp. difficulty: angular straggling ~8mrad
Coulomb excitation <θmax
How to distinguish nuclear excitation ?
How to separate nuclear absorption ?
solution:
relative measurement of B(E2)-values Qp g Qg MW
CATE Si
CsI
Target
200
Limit in scattering angles 0.6o to 2.8o corresponds to impact parameters: 40 to 10 fm
dσ/dθp [arb.]
scattering angle θp [deg]

8. MSU experiment: Neutron-rich Ti isotopes and possible N=32 and N=34 shell gaps
Eg [keV]
B(E2;0+→2+) [e2fm4]
Prev. work [e2fm4]
52Ti
1050
567(51)
54Ti
1497
357(63)
---
56Ti
1123
599(197)
Coulomb + nuclear excitation
(model dependent)
new lifetime measurement for 52Ti needed
D.-C.Dinca et al. Phys. Rev. C71 (2005)
B.A. Brown et al. Phys. Rev. C14 (1976) 1016

9. Relativistic Coulomb Excitation of Nuclei Near 100Sn
Collaboration: Lund, Uppsala, Stockholm, Keele, Legnaro, Warsaw, Debrecen, Liverpool, Surrey, York, GSI
Spokesperson: C. Fahlander, Lund, M. Gorska, GSI
ORNL data
RISING
B(E2, 2+->0+) values provide E2 correlations related to core polarization.
Lifetime measurements hampered by low-lying isomeric 6+ states in even
Sn isotopes up to 102Sn
2+->0+ decay too fast for electronic timing methods.
Coulomb excitation of instable Sn isotopes

10. Relativistic Coulomb Excitation of Nuclei Near 100Sn
Primary beam: 124Xe: 700 MeV/u
Secondary beam:
112Sn: 147 MeV/u, /s, 35 hours
108Sn: 142 MeV/u, /s, 24 hours
Coulomb excitation:
Au-target: 400 mg/cm2
Limited statistics due to VXI failure
(2/3 of uncorrelated data, low efficiency
with five Clusters at outer detector rings)
Preliminary B(E2, 2+->0+) value:
108Sn: /- 2.0 W.u.
Theory:
108Sn: W.u.
M. Hjorthen-Jensen, priv. com.
108Sn: W.u.
E. Caurier, F. Nowacki, priv. com.
112Sn (2+  0+)
108Sn (2+  0+)
results from A. Banu, M. Gorska, GSI