Plunger Measurements of Shape Coexistence in the Neutron Deficient 174 Pt Nuclei HEIDI WATKINS 2009 IoP NUCLEAR PHYSICS CONFERENCE UNIVERSITY OF BIRMINGHAM
OVERVIEW Physics Motivation. Shape Coexistence approaching Z = 82 shell gap. Experimental Techniques. Recoil distance Doppler-shift lifetime measurements (RDDS). Status of Analysis. Lifetime Analysis of 174 Pt.
E (ħ ) SHAPE COEXISTENCE GROUND STATE (Weakly Deformed) 2 EXCITED (Well Deformed) A phenomenon where nuclear configurations at similar excitation energies are built on very different deformations. Shape coexistence is expected to occur in transitional regions between weakly and strongly deformed ground states.
SHAPE COEXISTENCE NEAR THE Z=82 SHELL CLOSURE SPHERICAL OBLATE PROLATE 0p-0h 2p-2h 4p-4h The three different shapes are observed in three separate bands in 186 Pb. A. Andreyev et al. Nature 405 (2000) 430
SHAPE COEXISTENCE NEAR THE Z=82 SHELL CLOSURE Shape coexistence observed in 174 Pt is a result of band crossing between two minima. The deformation can be inferred from the experimental measurement of the lifetime of the state. 1 Q t The amount of mixing between these shapes can be determined by the reduced transition probabilities. 2 2 B( E2) Qt GD Dracoulis et al. Phys. Rev. C 44, R1246 (1991)
EXPERIMENTAL TECHNIQUE FAR FROM STABILITY Region of Interest The Segre Chart of Nuclides
EXPERIMENTAL TECHNIQUES FUSION EVAPORATION 86 Sr 16+ + 1mgcm -2 92 Mo @ 401MeV GREAT Focal Plane Spectrometer RITU Gas Filled Recoil Separator JUROGAM (Phase II) 15 Ge + 12 Clover detectors
EXPERIMENTAL TECHNIQUES - RDT Pixels of the DSSD a
EXPERIMENTAL TECHNIQUES - RDDS Plunger is specifically developed by the University of Koln to utilise the RDT technique. The device is coupled to Jurogam + RITU. 1 mgcm -2 Mg degrader foil.
EXPERIMENTAL TECHNIQUES - RDDS Beam current I B ~ 2pnA. RITU transmission decreased by 2/3. E E 0 1 v c cos Dv/c is small 1.1% 4.4% 3.3%. Detector angles 5 @ 158 o 10 @ 134 o
Counts CURRENT ANALYSIS 174 Pt 174 Pt Alpha Tagged Jurogam Spectra 394 497 & 501 461 474 Energy / kev Fully Doppler-shifted 174 Pt g-ray spectra from the plunger data. J TM Goon et al., Phys. Rev. C 70, 014309 (2004)
465 kev 477 kev 462 kev 474 kev
LIFETIME MEASUREMENT OF THE 6 + STATE A measurement for the lifetime of the 6 + state of 174 Pt: 2.2 (8) ps. This lifetime corresponds to a quadrupole moment of: Q = 7 (2) eb. A deformation parameter of: b 2 = 0.27 (7). A reduced transition probability of: B(E2) = 1.5 (9) (eb) 2. The analysis of these measurements is on going. TRS calculations predict a very g-soft gs with b 2 ~0.13 and a shape change to b 2 ~ 0.21 GD Dracoulis et al.
CONCLUSION / OUTLOOK Extract the quadrupole moments of the oblate and prolate configurations of 175 Au. Also to compare the relative deformations of 175 Au and 174 Pt to investigate the core-polarising properties of single-proton states.
COLLABORATORS T. Grahn, D.T Joss, L Bianco, P.A Butler, R Carroll, R.D Herzberg, J Pakarinen, R.D Page, E.S Paul, A Petts, J Revill, S Rigby, P.J Sapple, M Scheck, J Thomson. T Back, B Cederwall, M Sandzelius. I.G Darby. A Dewald, C Fransen, M Hackstein, T Munchen, T Pissalla, W Rothen. T Faestermann, R Gernhauser, T Kroll, R Krucken, P Maierbeck. P.T Greenless, U Jacobsson, P.M Jones, R Julin, S Juutinen, S Ketelhut, M Leino, M Nyman, P Nieminen, P Peura, P Rahkila, P Ruotsalainen, J Saren, C Scholey, J Sorri, J Uusitalo. D O Donnell, M Labiche, J Simpson. O Moller. N Lumley.
SHAPE COEXISTENCE NEAR THE Z=82 SHELL CLOSURE The nuclei 175 Au provide a unique opportunity to investigate the shape driving properties of proton excitations. The deformation can be inferred from the experimental measurement of the lifetime of the state. 1 Q t 2 FG Kondev et al., Phys. Lett. B512 (2001) 268
CURRENT ANALYSIS 175 Au 175 Au D O Donnell et al performed a Fusion Evaporation Reaction 92Mo(84Sr,p2n)175Au* @ 403MeV at JYFL. Additional bands observed as a result of the orbital of the unpaired proton.
EXPERIMENTAL TECHNIQUES - DDCM Lifetimes are derived using the Differential Decay Curve Method DDCM. ( d) i Q Q ( d) ( d) b R R ( d) ( O) dq I h J hi / J ( d) / dt s I d ( d) ( d) I d Q hi ( d) ( d) s Where I is the area of the Doppler shifted component d and I is the area of the degraded component of the g-ray peaks corresponding to the transition L i L j. Also b is the branching ration of the transition i j and J hi and J are the relative intensities of the g-ray transitions.
EXPERIMENTAL TECHNIQUES - DDCM The resulting lifetime is a weighted average of the values (d) corresponding to the different target-to-distance distances d. The values of (d) determined inside the region of sensitivity should be constant. Only direct feeding transitions to the level of interest have to be considered. Errors of the lifetimes are determined by the statistical errors Intensities of the degraded and full Doppler-shifted components of g-rays The error introduced determining the derivative of the decay curve.