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

Lo Bianco potential

• experiment: e−- coincidences at LNS

• model calculations for transitional nuclei with the

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

T. Kibedi et al., NPA567, 183 (1994)

Obvious approach: Measure spectra

of conversion electrons!

02+

01+

21+

767.8 KeV E2 893.6 KeV

E0

160Er

Ω : J. Kentele, NIM A271, 625 (1988)

= 42

J.O.Rasmussen, NP 19, 85 (1960)

Mini-orange spectrometer

beam

target

J.van Klinken and K. Wisshak, Nucl. Instr. Meth. 98 (1972) 1

Experiment

populated in (HI,xn)-reaction

the decay goes through low-spin states

156Dy ← 156Ho ← 156Er

160Er ← 160Tm ← 160Yb

19.5 min56 min

4.8 min9.4 min

enhanced population of low-spin non-yrast states

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.

156Dy

-ray spectrum

electron spectrum

Off-beam ICC Spectrum: 0+

2 → 0+1

transition in 156Dy

156Dy

Results for 156Dy

PhD thesis of Sara Nardelli, Camerino 2010

7030

800

3600

2000

1600

3200

2800

2400

400

1200

848830815800785770755740725710

0

8000

4000

2000

6000

760.5 906767.5 782.5 797.5 812.5 827.5 842.5 857.5 872.5 887.5

E0882.5

879.6

872.5

861.7854.6

* *838.9

826.6

797.5

768E2

765.7

768K765.7K

728.4L

738.9L 797.5K

826.6K

838.9K

854.6K

861.7K872.5K

882.2K 879.6K

836.1E0

854.6L

*

Energy in KeV

Nu

mb

er o

f co

un

ts -ray spectrum

electron spectrum

160Er

160Er : 768K(710.5KeV)160Dy: 766K (713KeV)

2 2+ +2 1E ; 0 0 0+ +

2 1E ; 0 160Er: 837.0 KeV

X value: X = 0.19(7)X = 0.19(7), after a careful consideration of all possible contaminants

2e ke e

e k e k

A (Er) (Er)A (Er) A (E ) = 2728 898

[A (Er) (Er) A (Dy) (Dy)]

PhD work of Shinjinee Das Gupta, Camerino

Results

156Dy 160Er

q2 1.9(7) 3(2) 4.8(1.6)

X(E0/E2) 0.045(17) 0.08(5) 0.19(7)

0.11(6) 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 - 203+ (1 - )0

22); 0 1; critical point at =1/2

Lo Bianco potential

sphericalside 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 !