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Picosecond Lifetime Measurements in ‘Vibrational’ Cadmium and Palladium Isotopes Paddy Regan Department of Physics, University of Surrey Guildford, GU2.

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Presentation on theme: "Picosecond Lifetime Measurements in ‘Vibrational’ Cadmium and Palladium Isotopes Paddy Regan Department of Physics, University of Surrey Guildford, GU2."— Presentation transcript:

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2 Picosecond Lifetime Measurements in ‘Vibrational’ Cadmium and Palladium Isotopes Paddy Regan Department of Physics, University of Surrey Guildford, GU2 7XH, UK p.regan@surrey.ac.uk

3 Survey of Even-Even Cadmium Isotopes A. Aprahamian et al., Phys. Lett. B 140, 22 (1984)

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5 Nomically ‘vibrational’ nuclei agree very well with CSM, (rotational) description.  i x = 10 h = ( h 11/2 ) 2

6 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 105-109 Cd, from the B(E2: 15 / 2 - → 11 / 2 - ) value rotational structure associated with rotational alignment coupling (RAC) † B(E2: 15 / 2 - → 11 / 2 - ) for 107 Cd 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

7 Crossing and alignments well reproduced by CSM, but AHVs see PHR et al., Phys. Rev. C68 (2003) 044313

8 PHR, Beausang, Zamfir, Casten, Zhang et al., Phys. Rev. Lett. 90 (2003) 152502  i x =10h

9 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 (h 11/2 ) orbitals). PHR, Beausang, Zamfir, Casten, Zhang et al., Phys. Rev. Lett. 90 (2003) 152502

10 Alignment (rotational picture at least) driven by Coriolis interaction on high-j, low-  orbitals (ie. ones with large j x on collective rotation axis. V cor = -j x.  eg. h 11/2 [550]1/2 ‘intruder’ FS for N~57,  2 ~0.15->0.2 jxjx 50 82 [550]1/2 - 1h 11/2 1g 9/2 [541]3/2 - see PHR, G.D. Dracoulis et al., J. Phys. G19 (1993) L157

11 Even-even yrast sequences and odd-A +ve parity only show rotational behaviour after ( h 11/2 ) 2 crossing….  seems to work ok, h 11/2 bands now look like rotors, PHR, C. Wheldon et al., Acta Phys. Pol. B36 (2005) 1313

12 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.)

13 B(E2: I -> 1-2) Theoretical Limits Vibrator: Rotor: U(5) limit (for 106 Cd): Rotor U(5) limit (for 106 Cd) Vibrator

14 Recoil (Doppler) Distance Method θ EsEs E0E0 12 C @ 60MeV 98 Mo 98 Mo( 12 C, xn) 110-x Cd 98 Mo( 12 C, αxn) 106-x Pd

15 SPEEDY and NYPD SPEEDY γ-ray array, 4 clovers each at 41.5° and 138.5°. New Yale Plunger Device: Thin target + 197 Au stopper. Piezoelectric motor to control target-stopper distance. Capacitance measured to give accurate distance value. R. Krucken et al.,J. Res. Nat. Inst. St.Tech. 105 (2000) 53.

16 RDM and DSAM Expts. at WNSL, August 2004 Experiment to determine the various B(E2) values of 103,4 Pd and 106,7 Cd Fusion-evaporation reaction used to produce the nuclei of interest 98 Mo( 12 C,3n) 107 Cd +,p2n) 107 Ag 98 Mo( 12 C,4n) 106 Cd +,p3n) 106 Ag 98 Mo( 12 C,  2n) 104 Pd 98 Mo( 12 C,  3n) 103 Pd

17 RDM and DSAM Expt. at WNSL, August 2004 RDM, 98 Mo target, ~900 μg/cm 2, v/c~0.7-.8% (~2  m/ps) DSAM, 98 Mo target.~500  g/cm 2 on 9 mg/cm 2 197 Au. 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

18 Differential Decay Curve Method (DDCM) Lifetime deduced from following equation: where For an intra-band direct feeding transition, the above equation reduces to Gate I hi = U hi + S hi I ij = U ij + S ij G. Bohm, A. Dewald et al., NIM A329 (1993) 248 S. Harrissopulos, Nucl. Phys. A683 (2001) 157

19 Differential Decay Curve Method C B A Direct Gating (on S B ) from above Nomenclature:U denotes “Unshifted” Transition S denotes “Shifted” Transition G. Bohm, A. Dewald et al., NIM A329 (1993) 248

20 Differential Decay Curve Method Inaccurate lifetimes may be obtained, for 2 + or 4 + gated due to “de-orientation’’. C B A Direct Gating (on U C ) from below

21 60 MeV beam energy

22 104 Pd: N=58 W. Andrejtscheff et al, Nucl. Phys. A448 (1986), 301 J.A. Grau et al, Phys. Rev. C14 (1974), 2297

23 Lifetime Plots for 2 + → 0 + in 104 Pd Average τ = 14.7(1.0)ps B(E2:2-0) = 36(2) W.u. forwardbackward S. Raman et al., At.Data Nucl.Data Tab. 36 1 (1987)  (2 +, 104 Pd) = 14.3(9)ps,

24 RDM DDCM Lifetime Analysis in 107 Cd 19 / 2 - 15 / 2 - 11 / 2 - 798keV 515keV

25 D.C. Stromswold et al, Phys. Rev. C17 (1978) 143

26 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 107 Cd 515 keV 798 keV = 28.2(1.0)W.u. = 24.5(4.3) W.u.

27 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 107 Cd.

28 B(E2) ratio plot for 11 / 2 - band in 107 Cd Vibrational Axial symmetric perfect rotor U(5) limit for 106 Cd B(E2: 15/2 -> 11/2) = 0.085e 2 b 2 = 28.2(1.0) Wu B(E2: 19/2 -> 15/2) = 0.074e 2 b 2 = 24.5(4.3) Wu B(E2: 23/2 -> 19/2) ~ 0.280e 2 b 2 = 100(17) Wu

29 106 Cd 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

30 106 Cd Challenges: Doublets P.H. Regan et al, Nucl. Phys. A586 (1995), 351

31 106 Cd: High Spin States

32 602 keV 12 + ->10 +    = 13(1) ps -> B(E2:12->10)= 27(2) Wu

33 ‘nti-magnetic rotation in 106 Cd, 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

34 Conclusions RDM (+DSAM) for B(E2)s in 106,7 Cd, 103,4 Pd B(E2) values for the 19 / 2 - and 15 / 2 - states in 107 Cd suggests rotational behaviour. Future work, B(E2)s for 106,107 Cd & 103,104 Pd (n,n’) work to get lower lying lifetimes in (stable) 106 Cd, see talk by A. Linnemann

35 Acknowledgements University of Surrey: P.H. Regan S.F. Ashley N.J. Thomas University of Paisley: K.L. Keyes A.Papenberg CCLRC Daresbury: D.D. Warner Yale University: E.A. McCutchan N.V. Zamfir R.F. Casten D.A. Meyer C. Plettner J. Vinson V. Werner E. Williams SUNY, Stony Brook: N. Pietralla G. Rainowski Clark University G. Gürdal Royal Institute of Technology, Stockholm: K. Andgren Istanbul University: L. Amon R.B. Cakirli M.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

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