GammaRay Spectroscopy of 120Ba

1
Two quasiparticle bands in 120Ba
Lee Angus Nuclear Physics Group University of the
West of Scotland Paisley Campus
Contents

• Physics motivation
• Two experiments with Gammasphere
• Data analysis Spectra, level scheme
• Results Angular distributions, mixing ratios,
  B(M1)/B(E2), alignment properties

2
Physics motivation

• Nilsson diagram for protons 50 Z 82
• Orbitals that are important in 120Ba
• Negative-parity h11/2 intruder levels
• Positive-parity g9/2 extruder levels
• Positive-parity g7/2 and d5/2 levels
• Octupole correlations predicted in nuclei
• with Fermi levels near to subshells with
• . In neutron deficient
  barium
• isotopes the h11/2 and d5/2 subshells satisfy
• this condition

3
Neutron-deficient A ? 120 region
http//ie.lbl.gov/toi/pdf/chart.pdf
4
Two experiments with Gammasphere

• Gs22
• 58Ni(64Zn265MeV,2p)120Ba
• 56 detectors
• Collimators on the detectors
• Larger number of triples !

• Gsfma6
• 58Ni(64Zn265MeV,2p)120Ba
• 101 detectors
• FMA
• Microball
• No collimators on detectors

5
Comparing the two Gammasphere experiments
100
24.8
48.3
29.4
0.13
0.03
is the normalized intensity of the 496 keV
transition in all cubes relative to the 496 keV
transition in the Gs22 ungated cube
6
Data Analysis
Band 1
Band 2
Band 2
7
Bands 3 and 4
Bands 3 and 4
8
Level scheme of 120Ba
p(g9/2 )-1h11/2
pg7/2 h11/2
9
Results

• Angular distributions have been
• measured for the strongest transitions
• in 120Ba
• A2/A0 and A4/A0 coefficients have been
• extracted allowing the multipolarities
• of the transitions to be determined, and
• spins and parities of the nuclear states
• to be inferred

• Mixing ratios were then extracted
• by taking a ?2 test of
• as a function of mixing ratio d

10
Reduced transition probability ratios B(M1) /
B(E2)

• Dönau and Frauendorf estimates of B(M1) / B(E2)
  are given by
• Parameters used to calculate estimates
• Experimental B(M1) / B(E2) is given by

11
Rotational alignments
12
Calculated alignment frequencies
13
Comparison of alignments in neighbouring barium
isotopes
14
Summary

• Two fusion evaporation experiments populating
  high spin states in 120Ba
• Rotational band and signature partner of lowest
  lying negative-parity band
• found
• Angular distributions and mixing ratios measured
  for the strongest transitions
• B(M1) / B(E2) ratios extracted and compared to
  theoretical estimates
• Alignment frequencies calculated using the
  cranked shell model have been
• compared to measured experimental alignment
  frequencies
• A signature dependence of the ?(h11/2)2
  alignment frequency has been
• observed

15
Collaborators
L.J. Angus1, J.F. Smith1, M.P. Carpenter5, C.J.
Chiara6, C.N. Davids 5, M. Devlin7, D.B. Fossan2,
S.J. Freeman8, I.M. Hibbert3, R.V.F.
Janssens5, D.R. LaFosse2, G.J. Lane 9, M.J.
Leddy8, I.Y. Lee4, A.O. Macchiavelli 4, P. Reiter
5, D.G. Sarantites6, D. Seweryniak5, K.
Starosta10, I.Thorslund2, R. Wadsworth3, A.N.
Wilson9, and J.N. Wilson11 1School of
Engineering and Science, University of the West
Scotland, Paisley PA1 2BE, UK 2State University
of New York, Stony Brook, NY 11794-3800,
USA 3Department of Physics, University of York,
Heslington, York YO1 5DD, UK 4Lawrence Berkeley
National Laboratory, Berkeley, CA 94720,
USA 5Argonne National Laboratory, Argonne,
Illinois 60439, USA 6Department of Chemistry,
Washington University, St Louis, Missouri 63130,
USA 7LANSCE-3, Los Alamos National Laboratory,
Los Alamos, New Mexico 87545, USA 8Schuster
Laboratory, University of Manchester, Manchester
M13 9PL, UK 9Department of Nuclear Physics,
Research School of Physical Sciences and
Engineering, Australian National University,
Canberra ACT 0200, Australia 10Michigan State
University, East Lansing, Michigan 48824,
USA 11CEA-SACLAY, DSM/DAPNIA/SPhN, F-91191
Gif-sur-Yvette Cedex, France
16
B(E1) / B(E2) ratios

• The experimental B(E1 ) / B( E2) ratio is given
  by

(1)

• B(E2) can be given by

(2)

• From TRS calculations

• B(E1) can then be found by substituting (2) into
  (1)

• The Weisskopf estimate for B(E1) and A 120 is