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 R. Kruecken - Yale University

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 R. Kruecken - Yale University

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

R. Kruecken - Yale University M1- bands across the Pb chain A rotational band in 199Pb Counts 125 166 215 268 323 377 430 482 532 573 618 100 200 300 400 500 600 700 800 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) ~ 20-40 (n /eb)2  rotational band in nucleus with spherical density distribution !? R. Kruecken - Yale University

G. Baldsiefen et al., Nucl. Phys. A 574, 521 (1994) R. Kruecken - Yale University

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!! R. Kruecken - Yale University

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 R. Kruecken - Yale University

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 440 450 Energy [keV] R. Kruecken - Yale University

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 R. Kruecken - Yale University

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

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] 0.0 0.2 0.4 0.0 0.2 0.4 Energy [MeV] R. Kruecken - Yale University

R. Kruecken - Yale University DSAM experiment on 198,199Pb Gammasphere -- 186W(18O,xn)198,9Pb Collaboration: Berkeley, York, Bonn , Livermore R.M.Clark et al., Phys. Rev.Lett. 78, 1868 (1997) DSAM experiment on 193-197Pb Gammasphere -- 172-6Yb(26Mg,xn)193-7Pb Collaboration: Berkeley, York, Bonn , Livermore R.M. Clark, R. Krücken et al. 197Pb 1000 500 400 200 600 300 100 400 410 440 450 460 470 Energy [keV] 403 keV 446 keV 467 keV 130º+145º 90º 35º+50º R. Kruecken - Yale University

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] R. Kruecken - Yale University

The Recoil Distance Doppler-Shift Method Target Stopper   1 - 1000ps 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] R. Kruecken - Yale University

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 R. Kruecken - Yale University

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

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) 200 250 300 350 2000 1000 1 mm 25 mm 11 mm 4.5 mm Energy [keV] R. Kruecken - Yale University

R. Kruecken - Yale University 20-,21- decay curves R. Kruecken - Yale University

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 R. Kruecken - Yale University

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 0.0 0.2 0.4 0.6 Rotational frequeny [MeV] R. Kruecken - Yale University

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

(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 R. Kruecken - Yale University

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 R. Kruecken - Yale University

R. Kruecken - Yale University Plunger Picture R. Kruecken - Yale University

R. Kruecken - Yale University Yrastball picture R. Kruecken - Yale University

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

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 R. Kruecken - Yale University

The backbending phenomenon in shears bands Rotational frequeny [MeV] 197Pb (2) Spin [] 12 10 8 6 4 2 B(M1) [N2] 0.0 0.2 0.4 0.6 0.8 Rotational frequeny [MeV] R. Kruecken - Yale University

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 R. Kruecken - Yale University

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) R. Kruecken - Yale University