Reiner Krücken - Yale University Reiner Krücken Wright Nuclear Structure Laboratory Yale University Why do we measure lifetimes ? The recoil-distance method (RDM) Recent achievements with the RDM Perspectives for RDM experiments * using transfer reactions * in fission fragments * using Coulex of the RIBs * using reactions with RIBs Precision lifetime measurements using the Recoil Distance Method

Reiner Krücken - Yale University Why measure lifetimes? our standard spectroscopic observables: E , I , W(  ), P   E x, B , J  lifetimes  and g-factors provide additional sensitive nuclear structure information direct measure of multipole moments: — E2  quadrupole moment Q 0  deformation of nucleus measure of shape/configuration mixing Absolute transition matrix-elements give clues on amount of mixing and shapes involved beforeafter a + b b + a

Reiner Krücken - Yale University Nuclear structure with lifetimes : Evolution of collectivity   2 (N,Z) Test of collective models  B(E2) vs.  [ exp. vs. model] Test of multi-phonon character of states  B(E2) of quadr. vibrational states deformation of superdeformed (SD) nuclei  Q t mixing of coexisting shapes  B(E2) is a sensitive measure decay out of superdeformed bands  Q t sensitive to mixing between SD and normal deformed states Test of new phenomena  Magnetic Rotation

Reiner Krücken - Yale University The Recoil Distance Doppler-Shift Method EuEu E s = E u (1+ v/c cos  )  Detector v ~ 1-2 % c in fusion reactions v u: unshifted s: shifted d TargetStopper Decay Curve d [  m] Standard Analysis:  2- fit with set of exponential functions. Feeding behavior as input of fit. No feedback of fit results.   ps  = ?

Reiner Krücken - Yale University Example: 126 Ba experiment with GASP shifted unshifted Spectra for backward detectors 100 Mo( 30 Si,4n) 126 Ba A. Dewald et al. PRC 54 (97) R2219 Decay curves for 4 +, 6 +, and 8 + states

Reiner Krücken - Yale University The Differential Decay Curve Method } L h  LiLi Lifetime value for each flight time t f A. Dewald et al., Z. Phys. A334 (1989) 163

Reiner Krücken - Yale University RDM in 198 Pb R. Krücken et al, PRC 58, R 1876 (98)  -curve Difference of unshifted intensities Slope of shifted intensity  = 0.70 (6) ps A B Gate  =? 198 Pb(3) (21 - ) -> (20 - ) 216keV A. Dewald et al., Z. Phys. A334 (1989) 163 The Differential Decay Curve Method in coincidence with feeding transitions

Reiner Krücken - Yale University Gammasphere

Reiner Krücken - Yale University The N. Y. P. D. design Inchworm Motor Feedback- Piezo  m-gauge-head Moving inner tube for target positioning Design by A. Dewald, Univ. of Köln, Germany Target Stopper

Reiner Krücken - Yale University The N.Y.P.D. (New Yale Plunger Device) based on Köln design by A. Dewald designed for large  -ray arrays like Gammasphere, YRAST Ball stable mechanical guidance for moving target  foils remain parallel at all times distance measurement using capacitance ( since heat expansion prevents mechanical measurement) LabView based feed-back system to stabilize distances in beam to better than 0.1  m (Jeff Cooper) possible combination with Rochester PPAC, CHICO and other charged particle detectors operational January 1999

Reiner Krücken - Yale University YRASTBALL

Reiner Krücken - Yale University Achievements of the RDM (biased view!) With current plunger design and multi-detector arrays it was possible to reach new benchmarks for RDM experiments: lifetimes in weakly populated (~1-10%) bands: – superdeformed bands in A~130/190 regions –   10-30%   Q t  5-10% – investigation of decay-out mechanism – limited by statistics and stability of distance sub-picosecond lifetimes in M1 bands – test of shears mechanism in 198 Pb – limited by statistics and stability of distance precision lifetimes of low-spin collective states – experiments in A~130 region with GASP –   2% achieved – sufficient statistics but limited by systematic errors

ND SD Spin 10: Decay out by mixing of cold superdeformed and hot spherical states Spin ~ 40: Cold superdeformed and spherical states are well separated Links Observed links and lifetime measurements have shown that: SD and ND states mix only weakly (1-4%) Decay of SD band is statistical : B(E1) ~ 8 x W.U. B(E2) < 5 x W.U. B(M1) < 5 x W.U. Decay Out Of Superdeformed Bands at A~190 Spin Energy [MeV] 10 5 Lifetimes { deformation 194 Pb

Reiner Krücken - Yale University Magnetic Rotation in Pb isotopes Prediction: Magnetic moments / B(M1) drop characteristically with increasing spin!! J Symmetry axis R JJ J Low spins high spins   R.M. Clark et al., PRL 78, 1868 (1997) Energy [keV] M1’s 199 Pb B(M1) [  N 2 ] Rotational frequency [MeV] New RDM New DSAM R. Krücken, R.M. Clark et al., PRC 58, R1876 (1998)  198 Pb

Reiner Krücken - Yale University Precision Lifetimes in the A~130 region Spin Q t (I  I-2)/ Q t (2  0) Ba 122 Xe 128 Ba 126 Ba 132 Nd 126 Xe Ratio of transition quadrupole moment shows shape changes with increasing spin. For some cases an impressive accuracy was achieved! P. von Brentano et al. GASP II

Reiner Krücken - Yale University Most basic experimental observables to follow shape evolution: E(2 + ) R 4/2 = E(4 + ) / E(2 + ) B(E2, 2 +  0 + ) Lifetimes in neutron rich nuclei at A~190 Hg Pt Os W Hf Yb Er E(2 + ) E(4)/E(2) B(E2) RDM experiments using transfer/ deep inelastic reactions involving the plunger and heavy-ion detectors

Reiner Krücken - Yale University Lifetimes in neutron rich nuclei at A~100 Kr 86 Sr 88 Zr Mo Ru Pd Cd stable lifetime and & others non-yrast states lifetime and non-yrast spin 0,2 states lifetime only 208 Pb + 18 O at 91 MeV (symmetric) 252 Cf spontaneous fission (asymmetric) Current situation in even-even nuclei around A~100

Reiner Krücken - Yale University Lifetimes of A~100 neutron rich nuclei via heavy ion induced fission Detector v ~ 3-4 % c v TargetStopper Little lifetime information for 4 + and above Shape coexistence in Sr and Zr isotopes Transitional region from Mo-Cd Claims of octupole correlations in Mo Claims of triaxiallity in 108,110 Ru  new territory for RDM experiments Solar cells, PPAC

Reiner Krücken - Yale University 104 Zr beam 10 6 p/sec Lifetimes of exotic beams at an ISOL facility (Inverse Kinematics Coulomb Excitation) Detector v 1 ~ 7.5 % c Coulex Target Retardation foil Ring of Plastic counters v1v1 1mg/cm 2 27 Al 2 mg/cm 2 27 Al v 2 ~ 6 % c 104 Zr 140 keV 312 keV 474 keV Coulex on 2nd foil Coulex on 1st foil Gate on maximal shifted part only Coulex on 1st foil v2v2 Gate

Reiner Krücken - Yale University Estimate of Statistics Zr nuclei per second with 300 MeV energy incident on 1 mg/cm 2 27 Al foil (v/c = 7.3%) Cross-sections for 104 Zr levels: mb mb mb mb coincidence Gammasphere (.09)GRETA (.4) (24 hrs)(6 hrs) (6 + | 4 + ) (8 + | 4 +, 6 + ) This should allow about 2% error for  (4 + ) !! Very sensitive experiment even with low intensity beams!

Reiner Krücken - Yale University Nuclear Structure near the proton drip-line drip-line nuclei are difficult to reach with stable beams and targets neutron deficient radioactive ion beams will allow new reactions with higher yields Lifetime measurements will be possible for N=Z nuclei such as 80 Zr  search for effects of proton-neutron pairing precision tests of shell model calculations around N=Z with accurate transition matrix elements