UNIVERSITY OF JYVÄSKYLÄ

Lifetime measurements probing triple shape coexistence in 175Au

Tuomas GrahnDepartment of Physics

University of Jyväskylä

The 11th International Conference on Nucleus-Nucleus Collisions

San Antonio, TX

27 May-1 June 2012

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 175Au.

Outlook – collectivity in the neutron-deficient Pb region.

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

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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).

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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

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JUROGAM II24+15 Ge+BGO detectors, eff. 6%RITU

Gas-filled recoil

separator,

transmission 20-50%

GREATFocal plane spectrometer

TDRTotal Data Readout, triggerless data acquisition system with 10 ns time stamping

Tagging instrumentation at JYFL

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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.

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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.

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175Au 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.

t1/2 = 139 (2) ms

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175Au RDDS experiment

Stable heavy-ion 86Sr beam from Jyväskylä K130 cyclotron at 401 MeV.

92Mo 1 mg/cm2 target, 1 mg/cm2 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).

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175Au RDDS experiment

Data analysed using differential decay-curve method (DDCM).

Mean lifetimes τ extracted for the 17/2+, 21/2+ and 25/2+ states.

Iπ = 17/2+

Constructed from singles RDT γ-ray spectra, recorded with ten JUROGAM Ge-detectors at 134°.

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Transition probabilities in 175Au

τ = 300-11000 ps

τ = 44(4) ps

τ = 11(2) ps

τ = 7(2) ps

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Transition duadrupole moments in the neutron-deficient Pb region

oblate

prolate

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Conclusions

The lifetimes of the low-lying yrast states in 175Au 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 i13/2 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.

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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.

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In collaboration with:

Oliver Lodge Laboratory, University of LiverpoolInstitut fü̈' r Kernphysik, Universität zu KölnInstitut fü̈r Kernphysik, TU DarmstadtPhysik-Department E12,TU Mü̈nchenSTFC Daresbury LaboratorySchool of Physics and Astronomy, University of ManchesterInstitute of Physics, Slovak Academy of Sciences