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 INFN sezione di Milano e Universita’ degli Studi di Milano

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 = 30,60,80,130,150,160,190 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 transitions • Low intensity •  ~ 10-4% channel • Highly fragmented decay •  high level density 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. Need other cases in different/similar mass regions 151Tb 196Pb 192Hg 152Dy N(2)path N(2)path Spin Spin Up to now full analysis performed only in 143Eu  proved the need to include tunneling effects S. Leoni at al. PLB 498(2001)137 To be also compared to 192Hg and 152Dy for which theory is available

7. 0.8-1.6 MeV Counts 1600 (Eg1 –Eg2) (keV) <Eg> = 532 keV 196Pb <Eg> = 1280 keV 300 1200 0.2-0.8 MeV 150 800 151Tb 400 0 -100 0 -50 50 100 (Eg1 –Eg2) (keV) Intensity % Eg [keV] Ridges in coincidence with SD yrast band 151Tb 151Tb FWHM [keV] Ridge <FWHM> = 11.7 keV Discrete trans SD ND Eg [keV] FWHMridge≈4×FWHMyrast Intensityridge≈ 3x Intensityyrast Ridge consists of many discrete bands

8. E T0 I I+2 I I-2 Fluctuation analysis Npath number of discreteunresolved bands forming the ridge 151Tb • Mean Npath = 25 151Tb • 45 196Pb tot matrix • 15 and 25 in direct coincidence Npath decreasing at low energies Theory overestimates Npath

9. Spacing of SD states ACTION NDSD EM decay width Spacing of ND states Pout Eexc Statistical model of decay-out Transmission coeff. SD Calculated along the tunneling path ND Probability to “fly out” from SD minimum 152Dy Vigezzi et al., PLB 249(1990)163. Gu and Weidenmuller, NPA660(1999)197 Yoshida, Matsuo and Shimizu NPA 696 (2001) 85-122.

10. 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 Theory  Iout =12  Exp.  Iout = 6  (Eexc = 0 MeV ) Need to use renormalization factors (pairing)

11. 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 • additional info on pairing (Cmass) and level density (Cr) Perspectives • MONTECARLO simulation to study decay flux in coincidence with SD yrast • Comparison with existing analysis on 192Hg • (T.L.Khoo and A.Lopez-Martens) Acknowledgments…

12. 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)

13. 300 150 Ridge 10  8.5 keV 6 FWHM[keV] SD Discrete trans 2 151Tb 196Pb ND 900 0 300 600 Intensity % Eg [keV] Intensity ofSD ridgevs. intensity ofyrast SD 196Pb

14. 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”