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Quasi-continuum studies in superdeformed 151 Tb and 196 Pb nuclei G. Benzoni Outline: SD decay out at T=0 and T0 The experiments Analysis Results Perspectives

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phase transition normal superfluid system Decay-out Feeding Plateau Intensity % E [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 SD ND Rigid body Super deformed band superfluid Counts * Pb SD band

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A.N. Wilson et al., Phys. Rev. Lett. 95 (2005) Evidences of discrete linking transitions in few nuclei High-energy transition Low intensity ~ % channel Highly fragmented decay high level density SD ND Pb 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

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A.Bracco and S.Leoni, Rep.Prog.Phys. 65 (2002) 299 Rotational motion at finite temperature (T0) 0 < U < 1-2 MeV 168 Yb RIDGE VALLEY Do SD ridges have same properties as discrete SD yrast band ??? (E 1 –E 2 ) (keV) Counts 2:1 I+2 I I-2 Regular bands 2:1 T 0 Ridges: unresolved discrete regular bands

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

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

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keV Ridge SD ND FWHM [keV] Discrete trans FWHM FWHM ridge 4×FWHM yrast Ridge consists of many discrete bands 196 Pb E [keV] = 11.7 keV FWHM [keV] SD ND Ridge Discrete trans 151 Tb = 532 keV (E 1 –E 2 ) (keV) 100 Counts (E 1 –E 2 ) (keV) = 1280 keV 151 Tb 196 Pb MeV MeV Ridges in coincidence with SD yrast band

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N path E [keV] Total Coincidence with yrast SD Fluctuation analysis N path number of discrete unresolved bands forming the ridge I+2 I I-2 T 0 I E 151 Tb N path N path decreasing at low energies Mean N path = Tb Pb tot matrix 15 and 25 in direct coincidence E [keV] N path total N path coincidence with SD Pb

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E [keV] Intensity % Intensity of SD ridge vs. intensity of yrast SD 151 Tb 196 Pb Ridge intensity is not yet decreasing N path E [keV] total o SD coinc.

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

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Actions decreasing at increasing spin decreasing at increasing E exc P out The ratio t /D ND governs P out Crossing point is I out Different behaviour for the 2 nuclei Decay-out properties (I out, E out ) expected to be different Easier to fly out Questa e troppo!!!

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no decay-out decay-out 143 Eu 151 Tb Cranked shell model T 0 N path E [keV] Results for 196 Pb Need to use renormalization factors Theory I out =12 Exp. I out = 6 (E exc = 0 MeV ) Results for 151 Tb comparison with theory including tunneling not yet ready Rescaled curve of 143 Eu already gives good agreement ND C ND S C mass S C = 2e-4 C mass = 3 No decay-out decay-out Different behaviour than 192 Hg already without tunneling

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Conclusioni Studio delle strutture SD nel nucleo 151 Tb a T 0 Analisi delle strutture a creste - : intensità n° di bande discrete (metodo delle fluttuazioni) Prospettive future Previsioni teoriche specifiche per il nucleo 151 Tb Simulazioni MONTECARLO per lo studio del flusso di decadimento SD anche in coincidenza con la banda yrast SD Comprensione del meccanismo di decadimento SD ND tramite tunneling quantistico FINE

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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, Milano, Italy A.Maj, M.Kmiecik Niewodniczanski Institute of Nuclear Physics, 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 , Stockholm, Sweden M.Matsuo, Y.R.Shimizu and E.Vigezzi for CSM calculations (Niigata University) (INFN Milano) Participants to the experiments

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