Lifetime measurement of 2 excitation in nuclei far away from stability

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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 110552, D-64291 Darmstadt, Germany A. Dewald,
K.O. Zell Institut für Kernphysik, Universität
Köln, Zülpicherstrasse 77, D-50937 Köln,
Germany R.K. Bhowmik, R. Kumar, S. Muralithar,
R.P. Singh Inter University Accelerator Centre,
New Delhi 110067, India S.K. Mandal,
Ranjeet Department of Physics Astrophysics,
University of Delhi, New Delhi 110007, India
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New Shell Structure at NgtgtZ Experiments
with N28-34 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 N32
• and N34?

Vst
56Ti22
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New Shell Structure at NgtgtZ Experiments
with N28-34 Nuclei

• Comparison 2 systematics
• and shell model calculations
• N32 for Z?24 (Cr)
• N32, N34 for Z ? 22 (Ti)
• Transition matrix elements?

TheoryGXPF1, GXPF1A M.Honma et al, Phys. Rev.
C65(2002)061301 KB3G E.Caurier et al,
Eur.Phys.J. A 15, 145 (2002)
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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, 082502 (2001) T. Otsuka et al., Eur. Phys. J.
A 13,69 (2002) M. Honma et al., Phys. Rev. C 69,
034335 (2004) E. Caurier et al., Eur. Phys. J. A
15, 145 (2002)
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Systematic Errors in Coulomb Excitation

• Angle measurement
• Nuclear correction

RIKEN 50 MeV/A MSU 40 MeV/A GANIL 30
MeV/A CERN 2 MeV/A
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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
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Tracking scattering angle determination

• Doppler corr. of measured g-rays
• ? impact parameter measurement
• Exp. difficulty
• angular straggling 8mrad
• Coulomb excitation lt?max
• How to distinguish nuclear excitation ?
• How to separate nuclear absorption ?
• Solution
• Relative measurement of B(E2)-values for
  different isotopes

200
Limit in scattering angles 0.6o to 2.8o
corresponds to impact parameters 40 to 10 fm
ds/d?p arb.
scattering angle ?p deg
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MSU experimentNeutron-rich Ti isotopes and
N32 and N34 shell gaps
Eg keV B(E20?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)
041302 B.A. Brown et al. Phys. Rev. C14 (1976)
1016
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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 ( 8.0 -2.1) ps
• 710 keV line contaminated by 72Ge(n,n') at 692 keV

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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

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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
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Lifetime Measurements on 52Ti
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Lifetime Measurements on 52Ti
Present Results Lifetime of 6 state in 52Ti
67.5 6.9 -4.9 ps 9 state in 52V 6.62 0.39
-0.31 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
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BE(2) values in light Sn isotopes

• Stable Sn isotopes fall in between magic shells
  at N50 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
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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

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Coulomb Excitation of Sn isotopes
Doppler Corrected Spectra ?
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Angular Distribution for Coulomb Excitation
qlab 15?- 45?
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EXPERIMENT PLANNED AT IUAC

• 190 MeV 58Ni beam on 112Sn target (1 abundance)
• Target to be enriched to gt99.5 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

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