1. UNIVERSITY OF JYVÄSKYLÄ Lifetime measurements probing triple shape coexistence in 175 Au Tuomas Grahn Department of Physics University of Jyväskylä The 11 th International Conference on Nucleus-Nucleus Collisions San Antonio, TX 27 May-1 June 2012

2. UNIVERSITY OF JYVÄSKYLÄ Outline Introduction – shape coexistence RDDS lifetime measurements with the JUROGAM γ-ray spectrometer at the Accelerator Laboratory of the University of Jyväskylä. Results – evidence of triple shape coexistence in the odd-A nucleus 175 Au. Outlook – collectivity in the neutron-deficient Pb region.

3. UNIVERSITY OF JYVÄSKYLÄ Accelerator Laboratory of the University of Jyväskylä - National Infrastructure status in Finland and Centre of Excellence status 2012-2017 of the Academy of Finland.

4. UNIVERSITY OF JYVÄSKYLÄ Shape coexistence A given atomic nucleus can exhibit eigenstates with different shapes, in most cases with similar binding energies. Unique to finite-body quantum system. `Shape coexistence in nuclei is a remarkable phenomenon that has evolved into a widespread feature that may occur in nearly all nuclei.´ - K. Heyde and J. L. Wood Rev. Mod. Phys. 83 1467 (2011).

5. UNIVERSITY OF JYVÄSKYLÄ Shape coexistence around Z=82 and N=104 Different shapes of an atomic nucleus (spherical, prolate, oblate…) coexist at similar excitation energies. Large valence particle space ⇒ residual quadrupole-quadrupole interaction drives the system into deformation. Unique laboratory to study shape coexistence, accessible by fusion- evaporation reactions and tagging techniques (JYFL) ⇒ lifetime (plunger) measurements. T. Grahn et al., Nucl. Phys. A 801, 83 (2008) Superdeformed Oblate Prolate

6. UNIVERSITY OF JYVÄSKYLÄ JUROGAM II 24+15 Ge+BGO detectors, eff. 6% RITU Gas-filled recoil separator, transmission 20-50% GREAT Focal plane spectrometer TDR Total Data Readout, triggerless data acquisition system with 10 ns time stamping Tagging instrumentation at JYFL

7. UNIVERSITY OF JYVÄSKYLÄ Recoil-Decay Tagging (RDT) method Beam from K130 cyclotron JUROGAM Ge- detector array RITU recoil separator GREAT spectrometer GREAT DSSD Power of the method: recoiling evaporation residue and its subsequent characteristic decay can be observed ⇒ provides unique tag for the prompt radiation.

8. UNIVERSITY OF JYVÄSKYLÄ Lifetime measurements at JYFL Recoil distance Doppler-shift (RDDS) lifetime measurements (plunger). Combined with selective recoil-decay tagging method. DPUNS plunger device commissioned May 2012.

9. UNIVERSITY OF JYVÄSKYLÄ 175 Au RDDS experiment Yrast states previously identified [F. G. Kondev et al., Phys. Lett. B 512, 268 (2001)]. Proposed oblate- prolate shape coexistence with the spherical alpha- decaying 11/2 - state. t 1/2 = 139 (2) ms

10. UNIVERSITY OF JYVÄSKYLÄ 175 Au RDDS experiment Stable heavy-ion 86 Sr beam from Jyväskylä K130 cyclotron at 401 MeV. 92 Mo 1 mg/cm 2 target, 1 mg/cm 2 degrader foil in the Köln plunger device ⇒ v/c = 4.4%. RDT singles γ-ray spectra Ten target to degrader distances ranging from 3 μm to 3000 μm. H. Watkins et al., PRC 84, 051203(R) (2011).

11. UNIVERSITY OF JYVÄSKYLÄ 175 Au RDDS experiment Data analysed using differential decay- curve method (DDCM). Mean lifetimes τ extracted for the 17/2 +, 21/2 + and 25/2 + states. I π = 17/2 + Constructed from singles RDT γ-ray spectra, recorded with ten JUROGAM Ge-detectors at 134°.

12. UNIVERSITY OF JYVÄSKYLÄ Transition probabilities in 175 Au τ = 300-11000 ps τ = 44(4) ps τ = 11(2) ps τ = 7(2) ps

13. UNIVERSITY OF JYVÄSKYLÄ Transition duadrupole moments in the neutron-deficient Pb region oblate prolate

14. UNIVERSITY OF JYVÄSKYLÄ Conclusions The lifetimes of the low-lying yrast states in 175 Au have been measured using the RDDS method at the University of Jyväskylä. Evidence for a triad of coexisting shapes at low spin. Collective prolate shape, based on an i 13/2 odd-proton configuration, is stabilised at high spin. Constraints for the B(E1) value from the 13/2 + state indicates a non-collective single-particle transition.

15. UNIVERSITY OF JYVÄSKYLÄ Outlook The DPUNS plunger device –Based on the Köln plunger design, constructed by University of Manchester. –Can operate in He of RITU ⇒ differential pumping. –Commissioned in May 2012. –Dedicated instrument for recoil separators RITU and MARA (under construction). Complementary transition probability studies at CERN-ISOLDE and JYFL.

16. UNIVERSITY OF JYVÄSKYLÄ In collaboration with: Oliver Lodge Laboratory, University of Liverpool Institut fü ̈ r Kernphysik, Universität zu Köln Institut für Kernphysik, TU Darmstadt Physik-Department E12,TU München STFC Daresbury Laboratory School of Physics and Astronomy, University of Manchester Institute of Physics, Slovak Academy of Sciences