1. Doppler-Shift Lifetime Measurements - The Yale Plunger -
Techniques for
Doppler-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
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2. 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
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3. 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
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4. R. Kruecken - Yale University
M1- bands across the Pb chain
A rotational band in 199Pb
Counts
125
166
215
268
323
377
430
482
532
573
618
4000
2000
Energy [keV]
M1’s
199Pb
R.M. Clark
et al., Phys.
Rev. Lett. 78,
1868 (1997)
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) ~ (n /eb)2
 rotational band in nucleus with
spherical density distribution !?
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5. G. Baldsiefen et al., Nucl. Phys. A 574, 521 (1994)
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6. Magnetic moments / B(M1) drop characteristically
The shears mechanism
Low spins
high spins J
Magnetic
Moments J  R  J
Symmetry axis
Magnetic moments / B(M1) drop characteristically
with increasing spin!!
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7. Signature of magnetic rotation B(M1) - values should drop with
Spin is generated by gradually closing of the
angle 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 electromagnetic
transition probabilities is characteristic:
B(M1) - values should drop with
increasing spin
B(M1) J
Lifetime measurements
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8. The Doppler Shift Attenuation Method
DSAM
Target
Stopper
Beam
Germanium
Detector
26Mg
@137MeV
Gold
172,4,6Yb
Continuous deceleration of recoil nuclei
Gamma-emission at range of velocities
 < 1ps
unshifted
600
400
200
maximum
Doppler-shift
Energy [keV]
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9. R. Kruecken - Yale University
Ingredients for DSAM analysis
Monte-Carlo simulation of stopping
time
velocity
model for
population
of levels
Known
feeding
Side-feeding
assumption
Q, are
effective
parameters
=?
Fit of spectrum  lifetime  B(E2) value
 B(M1) value
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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
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11. R. Kruecken - Yale University
Previous DSAM results
T.F. Wang et al.,
PRL 69, 21 (1992) 12 10 8 6 4 2 12 10 8 6 4 2
B(M1) [N2]
M. Neffgen et al.,
NPA595, 499 (1995) 12 10 8 6 4 2 12 10 8 6 4 2
B(M1) [N2]
Energy [MeV]
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12. R. Kruecken - Yale University
DSAM experiment on 198,199Pb
Gammasphere W(18O,xn)198,9Pb
Collaboration: Berkeley, York, Bonn , Livermore
R.M.Clark et al., Phys. Rev.Lett. 78, 1868 (1997)
DSAM experiment on Pb
Gammasphere Yb(26Mg,xn)193-7Pb
Collaboration: Berkeley, York, Bonn , Livermore
R.M. Clark, R. Krücken et al.
197Pb
1000
500
400
200
600
300
100
Energy [keV]
403 keV
446 keV
467 keV
130º+145º
90º
35º+50º
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13. Experimental proof of the shears mechanism in Pb nuclei
Gammasphere experiment- R.M. Clark, R. Kruecken et al.
Calculations by S. Frauendorf
B(M1) [N2]
B(M1) [N2]
B(M1) [N2]
What is going
on here?
Rotational frequency [MeV]
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14. The Recoil Distance Doppler-Shift Method
Target
Stopper
  ps v
v ~ 1-2 % c q
Detector d
u: unshifted
s: shifted Eu
Es = Eu (1+ v/c cos)
Decay Curve
Standard Analysis:
Fit with set of
exponential functions.
Feeding behavior as
input of fit.
No feedback of fit
results.
d [mm]
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15. R. Kruecken - Yale University
The Differential Decay Curve Method
} Lh
t=? Li
Lifetime value for each flight time tf
A. Dewald et al., Z. Phys. A334 (1989) 163
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16. 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)
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17. R. Kruecken - Yale University
RDM Experiment an 197,8Pb
Gammasphere, Köln Plunger,
154Sm(48Ca,xn)197,8Pb
Collaboration: Berkeley, Köln, Livermore
R. Krücken, R.M. Clark et al.
198Pb (3)
2000
1000
1 mm
25 mm
11 mm
4.5 mm
Energy [keV]
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18. R. Kruecken - Yale University
20-,21- decay curves
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19. Difference of unshifted
DDCM in coincidence
Gate
A.Dewald et al, Z. Phys.
A334 (1989) 163 A
=? B
-curve
 = 0.70 (6) ps
Difference of unshifted
intensities
Slope of shifted
intensity
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20. B(M1) values near the band head of a shears band in 198Pb
R.M. Clark et al., Phys. Rev. C50, 84 (1994)
New
DSAM
New
DSAM
Old
DSAM
RDM
B(M1) [N2]
RDM
RDM
Rotational frequeny [MeV] 10 5
New RDM
R. Kruecken,
R.M. Clark et al.
New
DSAM
B(M1) [N2]
Old
RDM
Rotational frequeny [MeV]
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21. R. Kruecken - Yale University

22. 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
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23. (New Yale Plunger Device)
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 mm (Jeff Cooper)
possible combination with Rochester
PPAC, CHICO
operational summer 1998
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24. R. Kruecken - Yale University
mm-gauge-head
for target positioning
Moving inner tube
Design by A. Dewald, Univ. of Köln
The N. Y. P. D. design
Feedback-
Piezo
Inchworm
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25. R. Kruecken - Yale University
Plunger Picture
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26. R. Kruecken - Yale University
Yrastball picture
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27. R. Kruecken - Yale University
Future perspectives
with the
N.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

28. Lifetimes of A~110 neutron rich nuclei via heavy ion induced fission
Solar cells,
PPAC
Target
Stopper v
v ~ 3-4 % c
Detector
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
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29. The backbending phenomenon in shears bands Rotational frequeny [MeV]
197Pb (2)
Spin [] 12 10 8 6 4 2
B(M1) [N2]
Rotational frequeny [MeV]
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30. Deformation of neutron rich nuclei around
A~190 via deep inelastic or transfer reactions
Most basic experimental observables to
follow shape evolution:
E(2+)
R4/2 = E(4+) / E(2+)
B(E2, 2+  0+) Hg Pt Os W Hf Yb Er
V. Zamfir
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31. 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)
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