Measurements of shape coexistence in 182,184Hg using
Coulomb excitation
CERN-ISOLDE (J. Cederkäll, P. Delahaye, D. Voulot, L.Fraile, F.Wenander)
CCLRC Daresbury Laboratory (B. Gomez, J. Simpson)
University of Edinburgh (T. Davinson, P. Woods)
University of Göttingen (K.-P. Lieb)
University of Jyväskylä (P.T. Greenlees, P. Jones, R. Julin, S. Juutinen)
KU Leuven (M Huyse, O. Ivanov, I. Stefanescu, J. Van de Walle and P. Van Duppen)
University of Liverpool (P.A. Butler, I. Darby, T. Grahn, R.-D. Herzberg, A. Hurst, G.D.
Jones, D.T. Joss, R.D. Page, E.S. Paul, J. Pakarinen, A. Petts)
University of Lund (A. Ekstrom, C. Fahlander)
TU-München ( T. Behrens, V. Bildstein, T. Fästermann, R. Gernhäuser, Th. Kröll, R.
Krücken, M. Mahgoub, P. Maierbeck)
University of Oslo (M. Guttormsen, A.-C. Larsen, S. Siem, N. U. H. Syed)
CEA-Saclay (E. Clement, C. Dossat, A. Goergen, W. Korten, J. Ljungvall, Ch. Theisen,
M. Zielinska )
University of Sofia (G. Rainovski)
HIL University of Warsaw (T. Czosnyka, J. Iwanicki, P. Napiorkowski, J. Srebrny, K.
Wrzosek)
University of York (D.G. Jenkins, B.S Nara Singh, N.S. Pattabiraman, R. Wadsworth)
Systematics of Hg isotopes
From Julin et al. J Phys G 27(2001)R109
Decay Schemes
a decay
4p-6h prolate
b~ +0.25
2 hole oblate
b~ -0.15
t measured
Old theory and isotope shifts
Hg isotopes
Faessler et al. (1972)
Quentin et al. (1973)
Nilsson et al. (1974)
182Hg
has prolate shape
Frauendorf et al. (1975)
Bengtsson et al. (1981)
182Hg
has weak oblate shape
Ulm et al. Z. Phys. A 325(1986)247
Recent theory
Nazarewicz et al.
PLB305 (1993)195
182,184Hg oblate
Yoshida and Takigawa
PRC55 (1997)1255
Moreno et al.
PRC73 (2006) 054302
Experimental Dilemmas
• Band-mixing analysis leads to the conclusion that
there is little mixing (< 4%) between the
bandheads
Wauters J et al. Z. Phys. A 345 (1993) 21, Phys. Rev. C 50 (1994) 2768
• Analysis if the a hindrance factor data suggests a
mixing of ~20%
Wauters J et al.
• Analysis of the E0 strength in 184Hg gives a mixing
of 0.5%
Heyde K and Meyer RA Phys. Rev. C 37 (1988) 2170
• Observed branching ratios for E2 decays in 184Hg
is best fitted if the sign of the deformation of the
two bands is the same
Guttormsen M Phys. Lett. 105B (1981) 99
Advantages of Coulex
Coulex will preferentially excite states strongly
coupled to the ground state so the oblate excited
states will be readily observed and identified
Low energy Coulex will measure the sign of the
diagonal quadrupole matrix element and hence
distinguish between prolate and oblate excitation
(Hurst et al, 70Se REX measurement submitted to PRL)
The degree of mixing between the oblate and
prolate structures is determined directly from
the transition matrix elements.
Calculated yields
transition
transition energy matrix element
(keV)
trans./diag. (eb)
-ray yields
2+1-0+1 oblate
352
-1.32/1.57
57800
2+1-0+1 prolate
352
1.32/-1.57
45800
4+2-2+1 oblate
578
-2.13/2.02
1360
2+2-0+1 prolate
549
0.13/-1.57
200
100 hours of 5 x 104 ions/s
Request
• Has been demonstrated that 238U can be
charge bred to A/q =4.6 with efficiency of ~ 4%
• Require 5 x 104 accelerated ions/s
• 3 shifts to test isobaric purity
• 3 shifts to set-up REX
• 6 shifts for 184Hg run
• 12 shifts for 182Hg run
Reorientation effect
P2+  <0||E2||2+>2 . [1 - <2+||E2’||2+> f()]
where  ~ E/(Ebeam)3/2
In our experiment P2+ changes by nearly
factor of 2 if <2+||E2’||2+> changes sign
Results: 70Se
Value from t measurement
Heese et al. 1986
PROLATE
OBLATE
Reproduce measured yield of 2-0
b2 ~ 0.3