picosecond lifetime measurements in ‘vibrational’ cadmium and palladium isotopes paddy regan...
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Picosecond Lifetime Measurements in ‘Vibrational’ Cadmium and Palladium Isotopes
Paddy ReganDepartment of Physics, University of Surrey
Guildford, GU2 7XH, UK
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Survey of Even-Even Cadmium Isotopes
A. Aprahamian et al., Phys. Lett. B 140, 22 (1984)
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Nomically ‘vibrational’ nuclei agree very well with CSM, (rotational) description.
ix = 10 h= (h11/2)2
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Odd-A Cadmium Isotopes: Vibrators or
Rotors ?• Odd-A Cd A = 105 – 123, all have a ‘rotational’ bands built upon the 11/2
- state
• For 105-109Cd, from the B(E2: 15/2- → 11/2
- ) value
rotational structure associated with rotational alignment coupling (RAC)†
• B(E2: 15/2- → 11/2
- ) for 107Cd suggests coupling
of unpaired neutron to vibrational core (PVC)‡† D.C. Stromswold et al, Phys. Rev. C 17 (1978) 143 F.M. Stephens, R.M. Diamond, S.G. Nilsson, Phys Lett B 44 (1973) 429
‡ O. Häusser et al, Phys Lett B52 (1974) 329 G. Alaga, V. Paar, V. Lopac, Phys Lett B43 (1973) 459 G. Dracoulis, R. Chapman et al., Part. Nucl. 4 (1972) 42
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Crossing and alignments well reproduced by CSM, but AHVs see PHR et al., Phys. Rev. C68 (2003) 044313
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PHR, Beausang, Zamfir, Casten, Zhang et al., Phys. Rev. Lett. 90 (2003) 152502
24
24
2 :Rotor
0 : Vibrator
)2(
242
),1(2
:Rotor
,2
:Vibrator
22
22
J
J
J
n
JR
JR
J
JJER
JEJJE
EJ
nE
ix=10h
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E-GOS plot appears to indicate that Vibrator-Rotator phase change is a feature of near stable (green) A~100 nuclei.
BUT….what is the microscopic basis ?
‘Rotational alignment’ can be a crossing between quasi-vibrational GSB & deformed rotational sequence.(stiffening of potential by population of high-j, equatorial (h11/2) orbitals).
PHR, Beausang, Zamfir, Casten, Zhang et al., Phys. Rev. Lett. 90 (2003) 152502
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Alignment (rotational picture at least) driven by Coriolis interaction on high-j, low- orbitals (ie. ones with large jx on collective rotation axis.
Vcor = -jx.
eg.
h11/2 [550]1/2 ‘intruder’
FS for N~57, 2~0.15->0.2
jx
50
82
[550]1/2-
1h11/2
1g9/2
[541]3/2-
see PHR, G.D. Dracoulis et al., J. Phys. G19 (1993) L157
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Even-even yrast sequences and odd-A +ve parity only show rotational behaviour after (h11/2 )2 crossing….
seems to work ok, h11/2 bands now look like rotors,
PHR, C. Wheldon et al., Acta Phys. Pol. B36 (2005) 1313
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B(E2) Signatures of Collectivity– For a perfectly harmonic oscillator:
– For axially deformed rotor (Bohr and Mottelson) :
– For U(5) of the IBA (valence limited case, see Casten and Warner, Rev. Mod. Phys. 60 (1988) 389 ; Kern et al., Nuc. Phys. A593 (1995) 21 .)
220
2 2016
5:2 KJKJQeJJEB ifif
NJJEB if :2
02:2 :2 EBNJJEB if
02:222
4
12:2 EB
N
INIIIEB
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B(E2: I -> 1-2) Theoretical Limits
0
50
100
150
200
250
0 5 10 15 20 25
Spin,
B(E
2: J → J
-2), W
.u.
Vibrator: 02:2 :2 EBNJJEB if
220
2 2016
5:2 KJKJQeJJEB ifif
Rotor:
U(5) limit (for 106Cd):
02:222
4
12:2 EB
N
INIIIEB
Rotor
U(5) limit (for 106Cd)
Vibrator
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Recoil (Doppler) Distance Method
θ
Es
E0
cos10 c
vEES
12C @ 60MeV98Mo
98Mo(12C, xn)110-xCd98Mo(12C, αxn)106-xPd
)()(10223.1
12
5522
sMeVEbeEB
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SPEEDY and NYPD
SPEEDY γ-ray array, 4 clovers each at 41.5° and 138.5°.
New Yale Plunger Device:Thin target + 197Au stopper. Piezoelectric motor to control target-stopper distance.Capacitance measured to giveaccurate distance value.
R. Krucken et al.,J. Res. Nat. Inst. St.Tech. 105 (2000) 53.
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RDM and DSAM Expts. at WNSL, August 2004
• Experiment to determine the various B(E2) values of 103,4Pd and 106,7Cd
• Fusion-evaporation reaction used to produce the nuclei of interest
98Mo(12C,3n)107Cd + ,p2n)107Ag98Mo(12C,4n)106Cd + ,p3n)106Ag98Mo(12C,α2n)104Pd98Mo(12C,α3n)103Pd
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RDM and DSAM Expt. at WNSL, August 2004
• RDM, 98Mo target, ~900 μg/cm2 , v/c~0.7-.8% (~2 m/ps)
• DSAM, 98Mo target.~500 g/cm2 on 9 mg/cm2 197Au.
• Distances 11, 14, 18, 23, 28, 41, 56, 127, 330, 2008 m.. (tof) ~ 22, 28, 36,46, 56, 82, 102, 154, 660, 4000 ps)
• 2 coincident γ-ray events within a time window of ~ 50ns
• (a ‘ b) matrices sorted for each plunger distance
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Differential Decay Curve Method (DDCM)
• Lifetime deduced from following equation: where
• For an intra-band direct feeding transition, the above equation reduces to
dx
xdQv
xQII
bxQ
xij
hhi
ij
hiijij
.
ijij
ijij SU
UQ
Gate
Ihi = Uhi + Shidt
dS
UUx
ij
hiij )(
Iij = Uij + SijG. Bohm, A. Dewald et al., NIM A329 (1993) 248S. Harrissopulos, Nucl. Phys. A683 (2001) 157
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Differential Decay Curve Method
dtdSU
xC
C)(
C
B
A
)()(10223.1
12
5522
sMeVEbeEB
Direct Gating (on SB) from above
Nomenclature: U denotes “Unshifted” Transition
S denotes “Shifted” Transition
G. Bohm, A. Dewald et al., NIM A329 (1993) 248
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Differential Decay Curve Method
• Inaccurate lifetimes may be obtained, for 2+ or 4+ gated due to “de-orientation’’.
C
B
A
BB
B
USdt
dU
x
)(
Direct Gating (on UC) from below
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60 MeV beam energy
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104Pd: N=58W. Andrejtscheff et al, Nucl. Phys. A448 (1986), 301
J.A. Grau et al, Phys. Rev. C14 (1974), 2297
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Lifetime Plots for 2+ → 0+ in 104Pd
Average τ = 14.7(1.0)psB(E2:2-0) = 36(2) W.u.
forward backward
S. Raman et al., At.Data Nucl.Data Tab. 36 1 (1987) (2+, 104Pd) = 14.3(9)ps,
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RDM DDCM Lifetime Analysis in 107Cd
dt
dS
Ux
ij
ij)( 19/2
-
15/2
-
11/2
-
798keV
515keV
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D.C. Stromswold et al, Phys. Rev. C17 (1978) 143
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K. Andgren, S.F.Ashley, PHR, E. McCutchan et al., in press J. Phys. G (2005)
cf. (15/2-) = 23.5(1.5)ps O. Häusser et al, Phys Lett B52 (1974) 329
DDCM Lifetime Analysis in 107Cd
515 keV 798 keV
= 28.2(1.0)W.u. = 24.5(4.3) W.u.
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Unevaluted report for 956 keV decay of Vishnevsky et al., ,Sov. Jour. Nucl. Phys. 54, 191 (1991) gives =1.15(43)ns -> B(E2:23/2- ->19/2-) = 30(11)Wu.
~0.36(6)ps
very preliminary !!not to be quoted
= 99.6 (16.5) W.u. !!
DSAM data can give information on higher lying (<1ps) lifetimes in 107Cd.
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B(E2) ratio plot for 11/2- band in
107Cd
0.87
0
1
2
3
4
5
5.5 7.5 9.5 11.5 13.5 15.5 17.5
Spin,
Vibrational
Axial symmetricperfect rotor
U(5) limit for 106Cd
B(E2: 15/2 -> 11/2) = 0.085e2b2 = 28.2(1.0) Wu B(E2: 19/2 -> 15/2) = 0.074e2b2 = 24.5(4.3) WuB(E2: 23/2 -> 19/2) ~ 0.280e2b2 = 100(17) Wu
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106Cd Challenges: Isomers
• τ = 90ns, four quasi-particle isomer at 4660 keV (12+)
• Various, ns isomers, associated with two quasi-particle configurations which feed low-lying states
W. Andrejtscheff et al, Nucl. Phys. A437 (1985), 167
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106Cd Challenges: Doublets
P.H. Regan et al, Nucl. Phys. A586 (1995), 351
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106Cd: High Spin States
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602 keV12+ ->10+
= 13(1) ps -> B(E2:12->10)= 27(2) Wu
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‘nti-magnetic rotation in 106Cd, A. Simons, R. Wadsworth et al., PRL 91 (2003)
B(E2:2+ –>0+) = 27 Wu
B(E2:4+->2+) = 44 Wu
B(E2:12+–>10+) = 27(2) Wu
B(E2:18+->16+) = 50(4) Wu
B(E2:20+->18+) = 47(6) Wu
B(E2:22+->20+) = 27(2) Wu
B(E2:24+->22+) = 20(2) Wu
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Conclusions
• RDM (+DSAM) for B(E2)s in 106,7Cd, 103,4Pd
• B(E2) values for the 19/2- and 15/2
- states in 107Cd suggests rotational behaviour.
• Future work, B(E2)s for 106,107Cd & 103,104Pd
• (n,n’) work to get lower lying lifetimes in (stable) 106Cd, see talk by A. Linnemann
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Acknowledgements
University of Surrey:P.H. ReganS.F. AshleyN.J. Thomas
University of Paisley:K.L. KeyesA. Papenberg
CCLRC Daresbury:D.D. Warner
Yale University:E.A. McCutchanN.V. ZamfirR.F. CastenD.A. MeyerC. PlettnerJ. VinsonV. WernerE. Williams
SUNY, Stony Brook:N. PietrallaG. Rainowski
Clark UniversityG. Gürdal
Royal Institute of Technology, Stockholm:K. Andgren
Istanbul University:L. AmonR.B. CakirliM.N. Erduran
Uni. de São Pãulo:R.V. Ribas
This work is supported by EPSRC (UK), U.S. Dept. Of Energy, under Grant No.DE-FG02-91ER-40609 and by the Yale University Flint and Science Development Fund
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