Diapositiva 1

1
Quasi-continuum studies in superdeformed 151Tb
and 196Pb nuclei
G. Benzoni

• Outline
• SD decay out at T0 and T?0
• The experiments
• Analysis
• Results
• Perspectives

2
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
Evidences of discrete linking transitions in few
nuclei

• 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

4
Rotational motion at finite temperature (T?0) 0
lt U lt 1-2 MeV
Ridges unresolved discrete regular bands
Do SD ridges 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
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???
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
Ridges in coincidence with SD yrast band
FWHM
196Pb
FWHMridge 4FWHMyrast
Ridge consists of many discrete bands
8
Fluctuation analysis
Npath ? number of discrete unresolved bands
forming the ridge
151Tb
Npath

• Mean Npath 25 151Tb
• 45 196Pb tot matrix
• 15 and 25 in direct coincidence

Npath decreasing at low energies
9
Intensity of SD ridge vs. intensity of yrast SD
151Tb
196Pb
? Ridge intensity is not yet decreasing
10
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, NPA660(1999)197 Yoshida, Matsuo and
Shimizu NPA 696 (2001) 85-122 .
11
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
12
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
Theory ? Iout 12 ? Exp. ? Iout 6 ?
(Eexc 0 MeV )
Need to use renormalization factors
13
Conclusioni

• 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)

FINE
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)