E0 DECAY OF THE 0+2 LEVELS IN 156DY AND 160ER
G. Lo Bianco, S. Nardelli, S. Das Gupta,
D.L. Balabanski, N. Blasi, K. Gladnishki, A. Saltarelli,
L. Fortunato
•
•
experiment: e−-
coincidences at LNS
model calculations for
transitional nuclei with the
Lo Bianco potential
The mini-orange spectrometer at LNS
E0 operator:
observables:
2(E0), r2
J.L.Wood et al., NPA651, 323 (1999)
very few data on E0 strength!
B(E2; yrast)/B(E2;rotor)
average of the N = 90 nuclei
(150Nd, 152Sm, 154Gd, 156Dy, 158Er)
average of the N = 92 isotones
average of “good” rotors in the
rare-earth and the actinide region
= 42
J.O.Rasmussen, NP 19, 85 (1960)
T. Kibedi et al., NPA567, 183 (1994)
Ω : J. Kentele, NIM A271, 625 (1988)
Obvious approach:
Measure spectra
of conversion electrons!
02+
767.8 KeV
E2
893.6 KeV
E0
21+
01+
160
Er
Mini-orange  spectrometer
beam
target
J.van Klinken and K. Wisshak, Nucl. Instr. Meth. 98 (1972) 1
Experiment
enhanced population of
low-spin non-yrast
states
populated in
(HI,xn)-reaction
the  decay
goes through
low-spin states
56 min
156Dy
← 156Ho ← 156Er
9.4 min
160Er
19.5 min
4.8 min
← 160Tm ← 160Yb
Measurements and calibrations
• absolute
efficiency calibration of Ge detectors;
• in-beam and off-beam -ray spectra;
• in-beam electron spectra for determination of the
transmission curve;
• off-beam electron spectra for ICC measurements
and X(E0/E2) calculation;
• independent ICC calibration, e.g. 124Sn(12C,4n)132Ba.
-ray spectrum
electron spectrum
156Dy
156Dy
Off-beam ICC
Spectrum:
0+2 → 0+1
transition in 156Dy
Results for
156Dy
PhD thesis of Sara Nardelli, Camerino 2010
8000
826.6
854.6
160Er
6000
4000
861.7
879.6
768
E2
797.5
765.7
872.5
838.9
882.5
E0
* *
*
Number of counts
2000
-ray spectrum
0
3600
760.5 767.5
782.5
797.5
812.5
827.5
842.5
857.5
872.5 887.5
882.2K
879.6K
906
3200
2800
2400
2000
1600
1200
728.4L
768K
765.7K
836.1
E0
826.6K
854.6K
872.5K
838.9K
861.7K
738.9L 797.5K
854.6L
800
400
electron spectrum
0
703 710
740
755
725
770
785
Energy in KeV
800
815
830
848
E2; 0  2
+
2
160Er
+
1
: 768K(710.5KeV)
160Dy: 766K (713KeV)
Ae (Er) 
E0; 0+2  01+
160Er:
837.0 KeV
Ae (Er)k (Er)
 A e (E2) = 2728  898
[Ae (Er)k (Er)  A e (Dy)k (Dy)]
X value: X = 0.19(7), after a careful consideration of all possible contaminants
PhD work of Shinjinee Das Gupta, Camerino
Results
156Dy
160Er
q2
1.9(7)
3(2)
X(E0/E2) 0.045(17) 0.08(5)

0.11(6)
4.8(1.6)
0.19(7)
0.14(11) 0.22(13)
T. Kibedi, R.H. Spear, ADNDT 89, 77 (2005)
X(5) is a solution of the Bohr
Hamiltonian with a special choice of
a potential v(,) = u() + v()
F.Iachello, Phys. Rev. Lett. 87, 052502 (2001)
For the U(5) – SU(3) shape phase
transition, a more general potential
in  was chosen
u() = V0(4 - 203+ (1 - )022);
0    1; critical point at  =1/2
Lo Bianco potential
spherical
side
close to the
critical point
Results of the calculations
a factor of 4 difference
with experiment;
* same true for the
-soft model
Bonnet et al., 79, 034307 (2009)
Conclusions and outlook
•A reliable technique for ICC measurements
was developed at the INFN LNS – Catania;
• First results for the X(E0/E2) ratio in 156Dy and
160Er were obtained;
• Calculations with a generalized potential in 
were performed, which allows to map the U(5) –
SU(3) phase shape transition;
• Further ICC measurements, as well as lifetime
measurements of 0+ states are in the pipeline.
Thank you !