Quasi-continuum studies in superdeformed 151 Tb and 196 Pb nuclei

1. Quasi-continuum studies in superdeformed 151Tb and 196Pb nuclei G. Benzoni • Outline: • SD decay out at T=0 and T≠0 • The experiments • Analysis • Results • Perspectives

2. 196Pb SD band Counts * 103 Super deformed band Rigid body superfluid ND SD Plateau Intensity % Feeding Decay-out Eg [keV] • SD bands are found in many nuclei • A = 80, 130, 150, 190 Typical intensity pattern: loss of intensity at low energies quantum tunneling btw SD and ND minima phase transition normal  superfluid system

3. SD 196Pb 3698 4062 ND Evidences of discrete linking transitions in few nuclei • High-energy transition  Eg > 3 MeV • Low intensity •  ~ ..% SD yrast A.N. Wilson et al., Phys. Rev. Lett. 95 (2005) Need for AGATA-like arrays What can we do already now ??? study of average properties of SD discrete excited bands  analysis of quasi-continuum spectra

4. Rotational motion at finite temperature (T≠0) 0 < U < 1-2 MeV 168Yb  VALLEY  RIDGE Counts 2:1 T0 2:1 (Eg1 –Eg2) (keV) Regular bands I+2 I I-2 Ridges: unresolved discrete regular bands Do SDridges have same properties as discrete SD yrast band ??? A.Bracco and S.Leoni, Rep.Prog.Phys. 65 (2002) 299

5. Two different nuclei in comparison 151Tb and 196Pb 27Al + 130Te  157Tb* Euroball, Strasburgo (Fr) Thin target, Ebeam = 155 MeV HECTOR 30Si + 170Er  200Pb* Thin target, Ebeam = 150 MeV BGO INNER BALL Ridges analysis: • - Moment of inertia ridge≈ yrast • Intensity of SD ridge • FWHM of SD ridge Comparison with cranked shell model calculations + decay out • Number of paths (discrete bands)

6. Why these nuclei??? No Decay-out 192Hg No Decay-out N(2)path N(2)path 152Dy Spin Spin Up to now full analysis performed in detail only in 143Eu S. Leoni at al. PLB 498(2001)137 151Tb and 196Pb close to these other studied cases  similar behaviour??? • decay out spin  30  for 152Dy while  10  for 192Hg • total number of paths  40 for 152Dy while  100 for 192Hg

7. 0.8-1.6 MeV Counts 1600 (Eg1 –Eg2) (keV) <Eg> = 532 keV 196Pb <Eg> = 1280 keV 1200 0.2-0.8 MeV Ridge 800 10 151Tb 400  8.5 keV 0 6 FWHM[keV] -100 0 SD -50 50 100 Discrete trans (Eg1 –Eg2) (keV) 2 FWHM [keV] Ridge <FWHM> = 11.7 keV ND 900 0 300 600 151Tb Discrete trans SD ND Eg [keV] Ridges in coincidence with SD yrast band 196Pb FWHMridge≈4×FWHMyrast Ridge consists of many discrete bands

8. E T0 I Npath total 120 196Pb Npath coincidence with SD-1 Total 90 Npath 60  57  38 Coincidence with yrast SD  28 30  20 Eg [keV] I+2 0 200 400 600 800 1000 I I-2 Eg[keV] Fluctuation analysis Npath number of discreteunresolved bands forming the ridge 151Tb Npath • Mean Npath = 25 151Tb • 45 196Pbtot matrix • 15 and 25 in direct coincidence with yrast SD Npath decreasing at low energies

9. total • SD coinc. Npath 300 150 Eg [keV] Intensity % Eg [keV] Intensity ofSD ridgevs. intensity ofyrast SD 151Tb 196Pb  Ridge intensity is not yet decreasing

10. Spacing of SD states ACTION NDSD 152Dy EM decay width Spacing of ND states Statistical model of decay-out Transmission coeff. SD Calculated along the tunneling path ND Probability to “fly out” from SD minimum Vigezzi et al., PLB 249(1990)163. Gu and Weidenmuller, NPA 660(1999)197 Yoshida, Matsuo and Shimizu NPA 696 (2001) 85-122.

11. Different behaviour for 151Tb and 196Pb Decay-out properties (Iout, Eout) expected to be different Pout Actions  decreasing at increasing spin decreasing at increasing Eexc  Easier to “fly out”

12. No decay-out Cranked shell model T ≠ 0 no decay-out 151Tb Npath decay-out 143Eu rND CrrND S  Cmass S • Cr = 2e-4 • Cmass = 3 Eg [keV] decay-out Results for 151Tb  comparison with theory including tunneling not yet ready Rescaled curve of 143Eu already gives good agreement Results for 196Pb Different behaviour than 192Hg already without tunneling Including tunneling Theory  Iout =12  Exp.  Iout = 6  (Eexc = 0 MeV ) Need to use renormalization factors

13. Conclusions • Investigation of SD excited bands in 151Tb and 196Pb • SD ridge structures found in both nuclei • Npath ~ 25 151Tb • ~ 45 196Pb in tot matrix • Comparison with cranked shell model calculations including tunneling • Good agreement for 196Pb…still to finalise for 151Tb Perspectives • MONTECARLO simulation to study decay flux in coincidence with SD yrast • Comparison with existing data on 192Hg • (T.L.Khoo and A.Lopez-Martens) Acknowledgments…

14. Participants to the experiments • G.Benzoni, S.Leoni, A.DeConto, D.Montanari, A.Bracco, N.Blasi, F.Camera, B.Million, O.Wieland • Dipartimento di Fisica, Universita’ degli Studi di Milano and INFN sezione di Milano, Via Celoria 16, 20133 Milano, Italy • Maj, M.Kmiecik • Niewodniczanski Institute of Nuclear Physics, 31-342 Krakow, Poland • B.Herskind • The Niels Bohr Institute, Blegdamsvej 15-17, 2100, Copenhagen • G.Duchene, J.Robin, Th.Bysrki, F.A.Beck, • Institut de Recherches Subatomiques, 23 rue du Loess,F-67037, Strasbourg, France • P.J.Twin • Oliver Lodge Laboratory, University of Liverpool, P.O. Box 147, Liverpool L69 7ZE, UK • A.Odahara, K.Lagergren • KTH,Royal Institute of Technology,Physics Department, Frescativägen 24,S-104 05, Stockholm, Sweden M.Matsuo, Y.R.Shimizu and E.Vigezzi for CSM calculations (Niigata University) (INFN Milano)

16. Different behaviour for the 2 nuclei Decay-out properties (Iout, Eout) expected to be different Pout Actions  decreasing at increasing spin decreasing at increasing Eexc Questa e’ troppo!!!  Easier to “fly out” The ratio Gt/DND governs Pout Crossing point is Iout

17. f(x,y) m1 f(x,y) f(x,y) Fit(x,y) m2 f(x,y) Fluctuation analysison g-g matrices f(x,y) = gaussian function (weigth) Fit(x,y)= 3rd orderpolinomialfit Number of paths To account for exp. resolution T. Døssing et al. Phys. Rep.268 (1996) 1