Picosecond Lifetime Measurements in ‘Vibrational’ Cadmium and Palladium Isotopes Paddy Regan Department of Physics, University of Surrey Guildford, GU2 7XH, UK [email protected]
Dec 14, 2015
Picosecond Lifetime Measurements in ‘Vibrational’ Cadmium and Palladium Isotopes
Paddy ReganDepartment of Physics, University of Surrey
Guildford, GU2 7XH, UK
Survey of Even-Even Cadmium Isotopes
A. Aprahamian et al., Phys. Lett. B 140, 22 (1984)
Nomically ‘vibrational’ nuclei agree very well with CSM, (rotational) description.
ix = 10 h= (h11/2)2
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
Crossing and alignments well reproduced by CSM, but AHVs see PHR et al., Phys. Rev. C68 (2003) 044313
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
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
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
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
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
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
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
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.
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
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
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
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
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
60 MeV beam energy
104Pd: N=58W. Andrejtscheff et al, Nucl. Phys. A448 (1986), 301
J.A. Grau et al, Phys. Rev. C14 (1974), 2297
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,
RDM DDCM Lifetime Analysis in 107Cd
dt
dS
Ux
ij
ij)( 19/2
-
15/2
-
11/2
-
798keV
515keV
D.C. Stromswold et al, Phys. Rev. C17 (1978) 143
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.
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.
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
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
106Cd Challenges: Doublets
P.H. Regan et al, Nucl. Phys. A586 (1995), 351
106Cd: High Spin States
602 keV12+ ->10+
= 13(1) ps -> B(E2:12->10)= 27(2) Wu
‘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
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
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