1. Lifetime measurement of 2+ excitation in nuclei far away from stability
IUAC
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
Inter University Accelerator Centre, 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
Neutron-rich Ca-, Ti-, Cr-Isotopes
few protons in 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?
Vst
56Ti22
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.

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. Comparison with large-scale shell-model calculation
Experimental 2+ energy high for 56Cr32
Experimental B(E2) value lower for 56Cr32 than for 54Cr and 58Cr
Theory does not reproduce the 56Cr B(E2) value
New Shell closure at N = 34 ??
Calculations:
T. Otsuka et al., Phys. Rev. Lett. 87, (2001)
T. Otsuka et al., Eur. Phys. J. A 13,69 (2002)
M. Honma et al., Phys. Rev. C 69, (2004)
E. Caurier et al., Eur. Phys. J. A 15, 145 (2002)

5. Systematic Errors in Coulomb Excitation
Angle measurement
Nuclear correction
RIKEN 50 MeV/A
MSU MeV/A
GANIL 30 MeV/A
CERN MeV/A

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

7. Tracking: scattering angle determination
Doppler corr. 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 for different isotopes 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 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. Direct measurement of B(E2) for 52Ti
B.A. Brown et al. Phys. Rev. C14 (1976) 1016
7Li + 48Ca at 28 MeV populated 51Ti, 52Ti, 52V
Lifetime measurements by RDM technique (singles)
1050 keV state a doublet !
Large uncertainties in extraction of B(E2) of 52Ti (2+ 0+) transition
t20 ~ 4.8 ( ) ps
710 keV line contaminated by 72Ge(n,n') at 692 keV

10. EXPERIMENT DONE AT NSC Experiment with RDM facility at GDA setup
7Li beam at 28 MeV
48Ca on stretched Au foil provided by GSI
Measurements done in g-g coincidence mode to eliminate contaminant transitions & side-feeding
Differential Decay Curve Method (DDCM) for life time extraction
Problems faced
6+ 4+ transition has long half-life ( ~ 35 ps)
Initial feeding of 2+ state sensitive to lifetime

11. Lifetime Measurements on 52Ti
48Ca targets supplied by GSI
RDM experiments with 7Li beam at IUAC
g-g spectra collected at different stopper distances
Oxidation of 48Ca target in transit prevented measurements below 20 mm distance

12. Lifetime Measurements on 52Ti

13. Lifetime Measurements on 52Ti
Present Results:
Lifetime of 6+ state in 52Ti = ps
9+ state in 52V = ps
Initial feeding of 2+ state in 52Ti could not be measured at the minimum distance of approach ( ~ 20 mm) limited by target wrinkles due to oxidation in transit
It will be useful to do a differential curve analysis

14. BE(2) values in light Sn isotopes
Stable Sn isotopes fall in between magic shells at N=50 & 82
B(E2) for Sn isotopes maximum at mid-shell
Large error bars for isotopes lighter than 116Sn
Measurements on 108Sn done earlier at GSI by Coulomb excitation
Accurate relative B(E2) for 112,114Sn / 116Sn required
Sn-isotopes
RIB

15. Coulomb Excitation at GSI
114, 116Sn beams of 3.6 MeV/A on 58Ni target.
Coulomb excitation of projectile and target
Two super-clovers used with electronics developed at IUAC
Participation by Rakesh Kumar, R.P. Singh and A. Jhinghan from IUAC

16. Coulomb Excitation of Sn isotopes
Doppler Corrected Spectra 

17. Angular Distribution for Coulomb Excitation
qlab = 15- 45

18. EXPERIMENT PLANNED AT IUAC
190 MeV 58Ni beam on 112Sn target (1% abundance)
Target to be enriched to >99.5% purity
Measurement of Coulomb excitation for 58Ni & 112Sn with g-rays to be detected in coincidence with scattered beam/recoils in annular position-sensitive PPAC developed at IUAC
qlab = 15 - 45
qcm = 23 - 67 for 58Ni & 90 - 150 for 112Sn
Cross-sections of ~ 120 mb expected for both projectile & target excitation
g to be detected by 4 Clover detectors at 153
Peak counts ~ 104 expected in 3 days of beam time
Total beam time requested 5 days including setup time