quasi-continuum studies in superdeformed 151 tb and 196 pb nuclei g. benzoni outline: sd decay out...
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Quasi-continuum studies in superdeformed 151Tb and 196Pb
nucleiG. Benzoni
Outline:•SD decay out at T=0 and T≠0•The experiments•Analysis•Results•Perspectives
phase transition normal superfluid system
600 800 1000 1200 1400 1600
10
25
50
75100
250
yrast SD
Decay-out
Feeding
Plateau
Inte
nsi
ty %
E [keV]
SD bands are found in many nucleiA = 30,60,80,130,150,160,190
Typical intensity pattern: loss of intensity at low energies
quantum tunneling btw SD and ND minima
SDND
E*
NORMAL minimum
SUPER deformed minimum
FEEDING of SD bands
DECAY-OUT of SD bands:Coupling betweenordered and chaotic states
Rigid body
Super
def
orm
ed b
and
superfluid
100 200 300 400 500 600 700 800
0
2
4
6E
E [ keV ]
Con
teggi (
Arb
. U
nits
*103 )
Cou
nts
* 1
03
196Pb SD band
A.N. Wilson et al., Phys. Rev. Lett. 95 (2005)
Evidences of discrete linking transitions in few nuclei
•High-energy transition • Low intensity
~ 10-4% channel• Highly fragmented decay
high level density
SD
ND
36984062
196Pb
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
= fn(, )
A.Bracco and S.Leoni, Rep.Prog.Phys. 65 (2002) 299
Rotational motion at finite temperature (T≠0)
0 < U < 1-2 MeV
= fn(, )
168Yb
R
IDG
E
V
ALLE
Y
Do SD ridges have same properties as discrete SD yrast band ???
-150 -100 -50 0 50 100 1500
1000
2000
3000
4000
5000
(E1 –E2) (keV)
Counts
282
E
2:1I+2I
I-2
Regular bands
2:1T0
Ridges: unresolved discrete regular
bands
HECTOR
Euroball, Strasburgo (Fr)
Two different nuclei in comparison 151Tb and 196Pb
BGO INNER BALL
Thin target, Ebeam = 155 MeV
27Al + 130Te 157Tb*
30Si + 170Er 200Pb*
Thin target, Ebeam = 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)
Why these nuclei???
• decay out spin 30 for 152Dy while 10 for 192Hg• total number of paths 40 for 152Dy while 100 for 192Hg
151Tb and 196Pb close to these other studied cases similar behaviour???
Up to now full analysis performed in detail only in 143Eu
750 1000 1250 1500 1750
E(keV)
0
20
40
60
80
N(2
) path
NPRID_CO May 25, 2001 12:37:10 PM
No Decay-Out
Decay-Out
152Dy
Spin
No Decay-out
N(2
) pat
h
Spin
N(2
) pat
h
No Decay-out
192Hg
S. Leoni at al. PLB 498(2001)137
0 300 600 900
2
6
10
8.5 keV
Ridge
SD
ND
FW
HM
[ke
V]
Discrete trans
FWHM
FWHMridge ≈ 4×FWHMyrast
Ridge consists of many discrete
bands
196Pb0
2
4
6
8
10
12
14
16
0 500 1000 1500 2000
E [keV]
<FWHM> = 11.7 keV
FW
HM
[k
eV
]
SD
ND
Ridge
Discrete trans151Tb
1600
1200
800
400
0
0-50 50-100
<E> = 532 keV
(E1 –E2) (keV)100-150 -100 -50 0 50 100 150
0
1000
2000
3000
4000
5000
C
ounts
(E1 –E2) (keV)
<E> = 1280 keV
151Tb
196Pb
100 200 300 400 500 600 700 800
0
2
4
6E
E [ keV ]
Conte
ggi (A
rb.
Units *
10
3 )
800 1000 1200 1400 16000,0
2,0x106
4,0x106
6,0x106
8,0x106
0.8-1.6 MeV
0.2-0.8 MeV
Ridges in coincidence with SD yrast band
0
5
10
15
20
25
30
35
40
45
50
900 1000 1100 1200 1300 1400 1500
Np
ath
E [keV]
Total
Coincidence with yrast SD
Fluctuation analysis
PN
N evepath
11
2
)2(
Npath number of
discrete unresolved bands forming the ridge
I+2I
I-2T0
I
E
151Tb
Npa
th
Npath decreasing at low energies
• Mean Npath = 25 151Tb
45 196Pb tot matrix
15 and 25 in direct coincidence
E[keV]
0 200 400 600 800 1000
Npath total
Npath coincidence with SD-1
57
38
20
28
196Pb120
90
60
30
600 800 1000 1200 1400 1600
10
100
yrast SD TOTALE in coincidenza yrast SD
E [keV]
Inte
nsi
ty % 150
300
100 200 300 400 500 600 700 800
10
100
SD ridge
yrast SD in coincidence with SD total
~300 %
Inte
nsity
%
E [keV]
~150 %yrast SD
Intensity of SD ridge vs. intensity of yrast SD
151Tb
196Pb
Ridge intensity is not yet decreasing
200 400 600 8000
20
40
60
80
100
120
140
~ 28
N(2
)
path
E [keV]
total in coincidence with SD yrast
~ 57
0
5
10
15
20
25
30
35
40
45
50
900 1000 1100 1200 1300 1400 1500
Np
ath
E [keV]
• totalo SD coinc.
path 0
E)(V(q(s))M2dsS(E)
152Dy
Statistical model of decay-out
Vigezzi et al., PLB 249(1990)163.Gu and Weidenmuller, NPA660(1999)197Yoshida, Matsuo and Shimizu NPA 696 (2001) 85-122 .
ND SD
1S2SDt )e(1
π2
DΓ
Spacing of SD statesACTION
ND
SD
ND
tout Γ
Γ
D
Γ
π2
1P EM decay width
Spacing of ND states
Calculated along the tunneling path
Transmission coeff.
Probability to “fly out” from SD minimum
ND
SD
0 10 20 30 40 500
1
2
3
4
5
6
7
8
9
10
S
Spin [hbar]
EExc
=0-4.0 MeV
Action for 151Tb (conf a)
0 10 20 30 40 500
1
2
3
4
5
6
7
8
9
10
S
Spin [hbar]
EExc
=0-4.0 MeV
Action for 196Pb (conf a)
Actions decreasing at increasing spin decreasing at increasing Eexc
0 10 20 30 40 50 600.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Nou
t
Spin [hbar]
EExc
=0-3.0 MeV
Pout
0 10 20 30 40 501E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100
1000
t/D
SD
/ND
Spin [hbar]
Eexc
=0 MeV
The ratio t/DND governs Pout
Crossing point is Iout
Different behaviour for the 2 nuclei
Decay-out properties (Iout, Eout) expected to
be different
Easier to “fly out”Questa e’ troppo!!!
0
20
40
60
80
100
120
600 800 1000 1200 1400 1600 1800
no decay-out
decay-out143Eu
151Tb
Cranked shell model T ≠ 0
Np
ath
E [keV]Results for 196Pb
Need to use renormalization factors
Theory Iout =12 Exp. Iout = 6 (Eexc = 0 MeV )
Results for 151Tb
comparison with theory including tunneling not yet
readyRescaled curve of 143Eu
already gives good agreement
ND C ND
S Cmass S — C = 2e-4— Cmass = 3
200 400 600 800 1000
0
50
100
150
200
250
196Pb
no decay out exp data192Hg no decay out c=1 c
m=1
c=1 cm
=3
c=2e-4 cm
=1
192Hg
N(2
)
path
E [keV]
No decay-out
decay-out
Different behaviour than 192Hg already without tunneling
Conclusioni
Studio delle strutture SD nel nucleo 151Tb a T ≠ 0
Analisi delle strutture a creste -:
•intensità
•n° di bande discrete (metodo delle fluttuazioni)
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
Comprensione del meccanismo di decadimento
SD ND tramite tunneling quantistico
FINE
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
A. Maj, M.KmiecikNiewodniczanski Institute of Nuclear Physics, 31-342 Krakow, Poland
B.HerskindThe 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.TwinOliver Lodge Laboratory, University of Liverpool, P.O. Box 147, Liverpool L69 7ZE, UK
A.Odahara, K.LagergrenKTH,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)
Participants to the experiments