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Techniques for 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 198 Pb The N.Y.P.D. Perspectives. Why are lifetimes important?.

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Techniques for Doppler-Shift Lifetime Measurements - The Yale Plunger -

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  1. 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

  2. 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

  3. 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

  4. 430 482 199Pb 268 377 323 4000 215 532 M1’s Counts 573 166 2000 618 125 100 200 300 400 500 600 700 800 Energy [keV] M1- bands across the Pb chain A rotational band in 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

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

  6. 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

  7. Signature of magnetic rotation 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

  8. 172,4,6Yb Gold Target Stopper Beam 26Mg @137MeV Germanium Detector The Doppler Shift Attenuation Method DSAM • Continuous deceleration of recoil nuclei • Gamma-emission at range of velocities  < 1ps unshifted 600 400 200 0 maximum Doppler-shift 440 450 Energy [keV] R. Kruecken - Yale University

  9. velocity time Ingredients for DSAM analysis • Monte-Carlo simulation of stopping • 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

  10. 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

  11. Previous DSAM results T.F. Wang et al., PRL 69, 21 (1992) 12 10 8 6 4 2 0 12 10 8 6 4 2 0 B(M1) [N2] M. Neffgen et al., NPA595, 499 (1995) 12 10 8 6 4 2 0 12 10 8 6 4 2 0 B(M1) [N2] 0.0 0.2 0.4 0.0 0.2 0.4 Energy [MeV] R. Kruecken - Yale University

  12. 1000 500 0 400 200 1000 500 0 600 400 200 300 200 100 0 600 400 200 0 35º+50º 600 400 200 300 200 100 0 600 400 200 0 446 keV 403 keV 467 keV 90º 130º+145º 400 410 440 450 460 470 Energy [keV] 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 R. Kruecken - Yale University

  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] R. Kruecken - Yale University

  14. The Recoil Distance Doppler-Shift Method Target Stopper   1 - 1000ps v ~ 1-2 % c v 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

  15. The Differential Decay Curve Method } Lh Li t=? Lifetime value for each flight time tf A. Dewald et al., Z. Phys. A334 (1989) 163 R. Kruecken - Yale University

  16. 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

  17. 2000 1000 1 mm 4.5 mm 2000 1000 11 mm 2000 1000 25 mm 2000 1000 200 250 300 350 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) Energy [keV] R. Kruecken - Yale University

  18. 20-,21- decay curves R. Kruecken - Yale University

  19. 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

  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 0 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

  21. R. Kruecken - Yale University

  22. 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  capacitancereliable • 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

  23. 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

  24. mm-gauge-head Moving inner tube for target positioning Design by A. Dewald, Univ. of Köln The N. Y. P. D. design Feedback- Piezo Inchworm R. Kruecken - Yale University

  25. Plunger Picture R. Kruecken - Yale University

  26. Yrastball picture R. Kruecken - Yale University

  27. 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 ~ 3-4 % c v 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

  29. The backbending phenomenon in shears bands 197Pb (2) Spin [] 12 10 8 6 4 2 0 B(M1) [N2] 0.0 0.2 0.4 0.6 0.8 Rotational frequeny [MeV] R. Kruecken - Yale University

  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 R. Kruecken - Yale University

  31. 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

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