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R. Kruecken - Yale University
Techniques forDoppler-Shift Lifetime Measurements
- The Yale Plunger -
Introduction
Magnetic Rotation
The DSAM technique
DSAM across the Pb chain
The RDM technique
The DDCM analysis
RDM in 198Pb
The N.Y.P.D.
Perspectives
R. Kruecken - Yale University
Why are lifetimes important?
• additional observable: Ex, J, B,
• measure of absolute matrix element:
• measure of electromagnetic moments:
Example:E2 transitions between rotational states
212
21 i),(
197
1
]!1)! [(2
1) ( 8),(
fE
)36.01(5
3
ndeformatio moment quadrupole
2)K-(I|IK20 EQ 1022.1
20
252t
91
ReZQt
R. Kruecken - Yale University
Where lifetimes are important:
• Evolution of collectivity 2(N,Z)
• Test of collective models B(E2) vs [ exp. vs model]
• Test of multiphonon character of states B(E2) of quadr. Vibrational states
• deformation of superdeformed (SD) nuclei Qt
• decay out of superdeformed bands Qt sensitive to mixing between SD and normal defomrmed states
• mixing of coexisting shapes B(E2) sensitive measure
• Test of new phenomena Magnetic Rotation
R. Kruecken - Yale University
M1- bands across the Pb chain
A rotational band in 199Pb
• very regular rotational band - but M1• several bands in light Pb isotopes• intensities between 1% and 10%• very large B(M1) values ( ~1-5 W.U.)• very weak quadrupole transitions :
B(M1)/B(E2) ~ 20-40 (n /eb)2
rotational band in nucleus with spherical density distribution !?
R.M. Clark et al., Phys. Rev. Lett. 78,1868 (1997)
Cou
nts
12
5
16
6
21
5
26
8
32
3
37
7 43
0
48
2
53
2
57
3
61
8100 200 300 400 500 600 700 800
4000
2000
Energy [keV]
M1’s
199Pb
R. Kruecken - Yale University
G. Baldsiefen et al., Nucl. Phys. A 574, 521 (1994)
R. Kruecken - Yale University
The shears mechanism
Symmetry axis
J
R
J
J
Low spinshigh spins
Magnetic moments / B(M1) drop characteristically with increasing spin!!
MagneticMoments
MagneticMoments
R. Kruecken - Yale University
Signature of magnetic rotation
Spin is generated by gradually closing of theangle between the large “single-particle” vectors
similar to the closing of the blades of a pair of sissors
Experimental signature:Spin-dependent behavior of the electromagnetictransition probabilities is characteristic:
B M( )12
B(M1) - values should drop with increasing spin
B(M1)
J
Lifetime measurements
R. Kruecken - Yale University
The Doppler Shift Attenuation MethodDSAM
• Continuous deceleration of recoil nuclei • Gamma-emission at range of velocities
Target Stopper
Beam
GermaniumDetector
26Mg@137MeV
Gold172,4,6Yb
Energy [keV]
unshiftedmaximum
Doppler-shift
600
400
200
0440 450
< 1ps
R. Kruecken - Yale University
Ingredients for DSAM analysis
• Monte-Carlo simulation of stopping
time
velo
city
Fit of spectrum lifetime B(E2) value B(M1) value
Side-feedingassumption
Knownfeeding
• model for population of levels
Q, are effective
parameters
Q, are effective
parameters
=?=?
R. Kruecken - Yale University
Uncertainties of DSAM experiments
• Feeding history is uncertain, since not all feeders are observed feeding model
• Gates from above could help but rarely enough statistics
• Little experimental data on stopping powers up to 15-20% systematic uncertainties
• in F() analysis constant Qt assumed
Relative DSAM measurements
• several nuclei populated in same reaction
• similar stopping for these nuclei
• relative lifetimes / Qt have no uncertainties from stopping power
good tool for comparison
R. Kruecken - Yale University
B(M
1) [ N
2 ]B
(M1)
[ N
2 ]
T.F. Wang et al., PRL 69, 21 (1992)
M. Neffgen et al., NPA595, 499 (1995)
Energy [MeV]0.0 0.2 0.4 0.0 0.2 0.4
12
10
8
6
420
12
10
8
6
420
12
10
8
6
420
12
10
8
6
420
Previous DSAM results
R. Kruecken - Yale University
1000
500
0
400
200
1000
500
0
600
400
200
300
200
100
0600
400
200
0
600
400
200
300
200
100
0600
400
200
0400 410 440 450 460 470 Energy [keV]
403 keV 446 keV 467 keV
130º+145º
90º
35º+50º
Gammasphere -- 186W(18O,xn)198,9PbCollaboration: Berkeley, York, Bonn , LivermoreR.M.Clark et al., Phys. Rev.Lett. 78, 1868 (1997)
DSAM experiment on 193-197Pb
Gammasphere -- 172-6Yb(26Mg,xn)193-7PbCollaboration: Berkeley, York, Bonn , LivermoreR.M. Clark, R. Krücken et al.
DSAM experiment on 198,199Pb
197Pb
R. Kruecken - Yale University
Experimental proof of the shears mechanism in Pb nuclei
Rotational frequency [MeV]
B(M
1) [ N
2 ]B
(M1)
[ N
2 ]B
(M1)
[ N
2 ]
What is going on here?
Gammasphere experiment- R.M. Clark, R. Kruecken et al.Calculations by S. Frauendorf
R. Kruecken - Yale University
The Recoil Distance Doppler-Shift Method
Eu Es = Eu (1+ v/c cos)
Detector
v ~ 1-2 % cv
u: unshifteds: shifted
d
Target Stopper
Decay Curve
d [m]
Standard Analysis:
Fit with set of exponential functions.
Feeding behavior asinput of fit.
No feedback of fit results.
1 - 1000ps
R. Kruecken - Yale University
The Differential Decay Curve Method
dt
td
ttt
dtthdttdtdt
td
dttit
ttdt
td
fi
hfhfi
i
fi
h th
tii
t
i
tifi
hh
hiii
III
nnn
nI
nnn
fff
f
)(
)()(1
)(
)( )( )(
)()( :Stoppeak of Area
)()( )(
dt
td
ttt
dtthdttdtdt
td
dttit
ttdt
td
fi
hfhfi
i
fi
h th
tii
t
i
tifi
hh
hiii
III
nnn
nI
nnn
fff
f
)(
)()(1
)(
)( )( )(
)()( :Stoppeak of Area
)()( )(
} Lh Li
Lifetime value for each flight time tf
A. Dewald et al., Z. Phys. A334 (1989) 163
R. Kruecken - Yale University
Advantages of the DDCM
• lifetime is only determined from observables
• lifetime is determined for each distance
(d) is sensitive to systematic errors
• with gates from above one selects a certain decay path
no sidefeeding
feeding history does not enter analysis as external parameter (it is automatically included)
R. Kruecken - Yale University
Energy [keV]
RDM Experiment an 197,8Pb
Gammasphere, Köln Plunger, 154Sm(48Ca,xn)197,8PbCollaboration: Berkeley, Köln, LivermoreR. Krücken, R.M. Clark et al.
200 250 300 350
2000
1000
2000
1000
2000
1000
2000
1000
1 m
25 m
11 m
4.5 m
198Pb (3)
R. Kruecken - Yale University
20-,21- decay curves
R. Kruecken - Yale University
DDCM in coincidence
A.Dewald et al, Z. Phys. A334 (1989) 163
-curve
Difference of unshiftedintensities
Slope of shiftedintensity
vdts
uu
dtddB
dAdBd
/|)(
)()()(
)()( dAdB uu
vdts
dt
ddB/|
)(
= 0.70 (6) ps
A
B
Gate
=?
R. Kruecken - Yale University
B(M1) values near the band head of ashears band in 198Pb
Rotational frequeny [MeV]
R.M. Clark et al., Phys. Rev. C50, 84 (1994)
B(M
1) [ N
2 ]
Old DSAMRDM
RDM
RDM
New DSAM
New DSAM
B(M
1) [ N
2 ]
Rotational frequeny [MeV]
R. Kruecken, R.M. Clark et al.
10
5
00.0 0.2 0.4 0.6
OldRDM
New RDM
NewDSAM
R. Kruecken - Yale University
R. Kruecken - Yale University
Technical requirements for the RDM
• minimize material around target for coincidence measurements with multi-detector system
• flat, clean and stretched foils roughness, dirt limit shortest distance
• accurate parallel positioning limit for shortest distance
• continuous distance measurement in beam capacitance method
• precision mechanics to keep relation distance capacitance reliable
• precision position measurement to calibrate capacitance measurement
• feedback mechanism to correct for thermal expansions piezo-crystal for corrections
• good heat conductivity to keep thermal expansions at their minimum
R. Kruecken - Yale University
The N.Y.P.D.(New Yale Plunger Device)
• based on Cologne design by A. Dewald
• designed for large -ray array like Gammasphere, Euroball, Yrastball
• stable mechanical guidance for moving target foils remain parallel
• distance measurement using capacitance
• LabView based feed-back system stabilizing distances in beam to better than 0.1 m (Jeff Cooper)
• possible combination with Rochester PPAC, CHICO
• operational summer 1998
R. Kruecken - Yale University
Th
e N
. Y
. P
. D
. d
esig
n
Inch
wo
rmF
eed
bac
k-P
iezo
m-g
aug
e-h
ead
Mo
vin
g in
ner
tu
be
for
targ
et p
osi
tio
nin
g
Des
ign
by
A. D
ewal
d, U
niv
. of
Kö
ln
R. Kruecken - Yale University
Plunger Picture
R. Kruecken - Yale University
Yrastball picture
R. Kruecken - Yale University
Future perspectives with theN.Y.P.D.
• Lifetimes of A~110 neutron rich nuclei via heavy ion induced fission
• Deformation of neutron rich nuclei around A~190 via deep inelastic or transfer reactions
• The backbending phenomenon in shears bands
• Lifetimes of (multi-)phonon states in nuclei
• Evolution of collectivity in the light actinides
• Test of the Q-phonon picture of the IBA
• Precision lifetimes for model tests
R. Kruecken - Yale University
Lifetimes of A~110 neutron rich nuclei via heavy ion induced fission
Detector
v ~ 3-4 % cv
Target Stopper
• Little lifetime information for 4+ and above
• Transitional region from Mo-Cd
• Claims of octupole correlations in Mo
• Claims of triaxiallity in 108,110Ru
new territory for RDM experiments
Solar cells,PPAC
R. Kruecken - Yale University
The backbending phenomenon in shears bandsB
(M1)
[ N
2 ]
Rotational frequeny [MeV]
0.0 0.2 0.4 0.6 0.8
1210 8 6 4 2 0
Sp
in []
197Pb (2)
R. Kruecken - Yale University
Deformation of neutron rich nuclei aroundA~190 via deep inelastic or transfer reactions
Most basic experimental observables tofollow shape evolution:
• E(2+)
• R4/2 = E(4+) / E(2+)
• B(E2, 2+ 0+)
Hg
Pt
Os
W
Hf
Yb
Er
V. Zamfir
R. Kruecken - Yale University
Summary
• Lifetimes are important observables of nuclear structure
Techniques:• DSAM for short lifetimes (< 1ps) (but some systematic problems involved)• relative DSAM is very powerful• RDM for lifetimes 1~1000 ps• DDCM analysis reduces systematic errors• N.Y.P.D. is a new exciting device
Physics:• Proof of Magnetic Rotation from lifetimes• Towards the “terra incognita”: - fission fragments - heavy rare earth nuclei via transfer / DI• Sensitive tests of nuclear models (Shell model as well as collective models)