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

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 transition 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)

Why these nuclei??? N(2)path 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??? 152Dy Spin No Decay-out N(2)path No Decay-out 192Hg decay out spin  30  for 152Dy while  10  for 192Hg total number of paths  40 for 152Dy while  100 for 192Hg

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 FWHM Eg [keV] <FWHM> = 11.7 keV FWHM [keV] SD ND Ridge Discrete trans 151Tb 300 600 900 2 6 10  8.5 keV Ridge SD ND FWHM [keV] Discrete trans 196Pb FWHMridge ≈ 4×FWHMyrast 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 Npath Eg [keV] Total Coincidence with yrast SD Eg [keV] 0 200 400 600 800 1000 Npath total Npath coincidence with SD-1  57  38  20  28 196Pb 120 90 60 30 151Tb Npath Mean Npath = 25 151Tb 45 196Pb tot matrix 15 and 25 in direct coincidence Npath decreasing at low energies

 Ridge intensity is not yet decreasing Npath Eg [keV] total SD coinc. Intensity of SD ridge vs. intensity of yrast SD Eg [keV] Intensity % 150 300 151Tb 196Pb  Ridge intensity is not yet decreasing

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

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

No decay-out decay-out rND  Cr rND S  Cmass S 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 Different behaviour than 192Hg already without tunneling 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

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

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)