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

SD bands are found in many nuclei A = 30,60,80,130,150,160,190 Typical intensity pattern: loss of intensity at low energies Rigid body Super deformed band superfluid Counts * 103 196Pb SD band Decay-out Feeding Plateau Intensity % Eg [keV] SD ND quantum tunneling btw SD and ND minima phase transition normal  superfluid system

196Pb Evidences of discrete linking transitions in few nuclei SD ND 3698 4062 196Pb 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

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

Two different nuclei in comparison 151Tb and 196Pb Euroball, Strasburgo (Fr) HECTOR Thin target, Ebeam = 155 MeV 27Al + 130Te  157Tb* 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)

151Tb 196Pb Up to now full analysis performed only in 143Eu  proved the need to include tunneling effects S. Leoni at al. PLB 498(2001)137 196Pb Need other cases in different/similar mass regions 151Tb 152Dy Spin N(2)path 192Hg To be also compared to 192Hg and 152Dy for which theory is available

Ridge consists of many discrete bands Ridges in coincidence with SD yrast band 1600 1200 800 400 -50 50 -100 <Eg> = 532 keV (Eg1 –Eg2) (keV) 100 Counts <Eg> = 1280 keV 151Tb 196Pb 0.8-1.6 MeV 0.2-0.8 MeV 151Tb Eg [keV] Intensity % 150 300 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

Npath  number of discrete unresolved bands forming the ridge Fluctuation analysis Npath  number of discrete unresolved 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

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

No decay-out rND  Cr rND S  Cmass S decay-out Results for 151Tb 143Eu 151Tb Cranked shell model T ≠ 0 Npath Eg [keV]  comparison with theory including tunneling not yet ready Rescaled curve of 143Eu already gives good agreement No decay-out decay-out Results for 196Pb Theory  Iout =12  Exp.  Iout = 6  (Eexc = 0 MeV ) Need to use renormalization factors rND  Cr rND S  Cmass S Cr = 2e-4 Cmass = 3 (pairing)

Conclusions Perspectives Acknowledgments… 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…

M.Matsuo, Y.R.Shimizu and E.Vigezzi for CSM calculations 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)

196Pb Intensity of SD ridge vs. intensity of yrast SD 151Tb 196Pb 300 600 900 2 6 10  8.5 keV Ridge SD ND FWHM [keV] Discrete trans 196Pb Intensity of SD ridge vs. intensity of yrast SD Eg [keV] Intensity % 150 300 151Tb 196Pb

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