UNIVERSITY OF JYVÄSKYLÄ Lifetime measurements probing triple shape coexistence in 175 Au Tuomas...

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

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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