1. E0 DECAY OF THE 0 + 2 LEVELS IN 156 DY AND 160 ER 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

2. The mini-orange spectrometer at LNS

3. E0 operator: observables:  2 (E0),  r 2  J.L.Wood et al., NPA651, 323 (1999)

4. very few data on E0 strength!

5. B(E2; yrast)/B(E2;rotor) average of the N = 90 nuclei ( 150 Nd, 152 Sm, 154 Gd, 156 Dy, 158 Er) average of the N = 92 isotones average of “good” rotors in the rare-earth and the actinide region

6. T. Kibedi et al., NPA567, 183 (1994) Obvious approach: Measure spectra of conversion electrons! Ω : J. Kentele, NIM A271, 625 (1988) = 4242 J.O.Rasmussen, NP 19, 85 (1960)

7. Mini-orange  spectrometer beam target J.van Klinken and K. Wisshak, Nucl. Instr. Meth. 98 (1972) 1

8. Experiment populated in (HI,xn)-reaction the  decay goes through low-spin states 156 Dy ← 156 Ho ← 156 Er 160 Er ← 160 Tm ← 160 Yb 19.5 min56 min 4.8 min 9.4 min enhanced population of low-spin non-yrast states

9. 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. 124 Sn( 12 C,4n) 132 Ba.

10. 156 Dy  -ray spectrum electron spectrum

11. Off-beam ICC Spectrum: 0 + 2 → 0 + 1 transition in 156 Dy 156 Dy

12. Results for 156 Dy PhD thesis of Sara Nardelli, Camerino 2010

13. Energy in KeV Number of counts  -ray spectrum electron spectrum 160 Er

14. 160 Er : 768K(710.5KeV) 160 Dy: 766K (713KeV) 160 Er: 837.0 KeV X = 0.19(7) X value: X = 0.19(7), after a careful consideration of all possible contaminants PhD work of Shinjinee Das Gupta, Camerino

15. Results 156 Dy 160 Er q2q2 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)

16. 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(  ) = V 0 (  4 - 2  0  3 + (1 -  )  0 2  2 ); 0    1; critical point at  =1/2 Lo Bianco potential

17. spherical side close to the critical point

18. Results of the calculations a factor of 4 difference with experiment; * same true for the  -soft model Bonnet et al., 79, 034307 (2009)

19. 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 156 Dy and 160 Er 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.

20. Thank you !