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Precision Determinations of the Transition Quadrupole Moments Approaching the N N Valence Maximum: Lifetimes of Yrast States in 166,168 Dy An GANIL Proposal P.H.Regan 1,10, J.Nyberg 2, J.Simpson 3, J.J.Valiente Dobon 4, P. John 5, A.Atac 6, B.Cederwall 6, A.Gengelbach 2, P.A.Soederstroem 7, Zs. Podolyak 1, N.Marginean 8, J.Ljungvall 9, P.M.Walker 1, W.N.Catford 1, G.Lotay 1,10, S.M.Judge 10 et al., 1 - University of Surrey, UK 2 - Uppsala University, Sweden 3 - STFC Daresbury Laboratory, UK 4 - INFN Legnaro, Italy 5 - INFN Padova, Italy 6 – Stockholm, Sweden 7 - RIKEN, Japan 8 - IFIN Bucharest, Romania 9 – CSNSN Orsay, France 10 – National Physical Laboratory, UK

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What underlies nuclear quadrupole deformation? 166 Dy 100 : Does the B(E2:2 + → 0 + ) (a) increase as the valence maximum is reached at N=104 ? or (b) reduce compared to 164 Dy 98 (the heaviest stable isotope) as the E(2 + ) systematics suggest? 166 Dy 100

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Skyrme Hartee-Foch and Projected Hartree Foch Mean-Field calculations for Dy isotopes which predict maximum deformation at either N=100 or N=102.

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Reminder: How is measuring the lifetime useful? Transition probability (i.e., 1/mean lifetime as measured for state which decays by EM radiation) (trivial) gamma-ray energy dependence of transition rate, goes as. E 2L+1 e.g., E 5 for E2s for example. Nuclear structure information. The ‘reduced matrix element’, B( L) tells us the overlap between the initial and final nuclear single-particle wavefunctions.

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Lifetimes expected to be in the ~2ns and ~200ps regimes for the I =2 + and 4 + yrast states respectively, from the Dy and N=102 systematics.

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Modified from Introductory Nuclear Physics, Hodgson, Gadioli and Gadioli Erba, Oxford Press (2000) p509 We can populate high-spin physics in neutron rich nuclei using binary collisions/multi-nucleon transfer. See classic DIC type papers e.g., Broda et al. Phys. Rev Lett. 74 (1995) p868 Juutinen et al. Phys. Lett. 386B (1996) p80 Wheldon et al. Phys. Lett. 425B (1998) p239 Cocks et al. J. Phys. G26 (2000) p23 Krolas et al. Acta. Phys. Pol. B27 (1996) p493 Asztalos et al. Phys. Rev. C60 (1999)

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166,168 Dy yrast states populated with CLARA+PRISMA experiment, gated on binary BLFs (Kr isotopes) to select Dy partners following the 82 Se+ 170 Er DIC / binary transfer reaction.

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166,168 Dy yrast states populated with CLARA+PRISMA experiment, gated on binary BLFs (Kr isotopes) to select Dy partners following the 82 Se+ 170 Er DIC / binary transfer reaction.

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Proposed Experiment 136 Xe beam on a thick 170 Er target with a thick 197 Au backing to stop the reaction residues. Emitted gammas from binary partner nuclei detected in a combined AGATA + 32 element LaBr 3 detection array. AGATA to select 166,168 Dy channels by (stopped) in-beam gates on higher-lying transitions in 166,168 Dy (from I =6 + and above) and also from isomeric decays in the barium binary partner nuclei, e.g., I =10 + isomer in 136 Ba. LaBr 3 -LaBr 3 coincidences between 6 + → 4 +, 4 + → 2 + & 2 + → 0 + yrast decays and from K X-rays following 2 + → 0 + internal conversion then used for a time difference analysis to determine B(E2:J→ J-2) values from the 4 + and 2 + states.

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136 Xe beam on a ‘thin’ 198 Pt target (850 MeV); GAMMASPHERE + CHICO. BLF stopped in view of GAMMASPHERE detectors.

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Clearly identify Os in binary partner channels via the 2p transfer; range from x=2 to 14 neutrons evaporated. We might expect a similar population in 170-x Dy isotopes following 136 Xe+ 170 Er reaction. 194 Os enhanced! 136 Xe+ 198 Pt CHICO + GAMMA SPHERE data J.J. Valiente-Dobon PhD thesis Surrey (2003)

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Combined AGATA Demonstrator and FATIMA Array 32 LaBr 3 detectors 1.5” diameter x 2” long in 2 rings of 16 detectors; with the AGATA demonstrator.

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T 1/2 = 1.4ns Tests with 152 Eu source to measure lifetime of I = keV level in 152 Sm.

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Count Rate Estimate (by J. Nyberg) Assumptions: (a) Beam: 136Xe, Energy ~ 900 MeV, current ~ 1pnA (could possibly take more) Target: 170Er, 1 mg/cm2 (could use thicker target with Au backing depending on final rates) Estimated production cross-section for 168Dy ~ 1mb. AGATA: 34 crystals at 23.5 cm FATIMA: 32 detectors 1.5” x 2 “ typical distance 15.6 cm Conclusion: for a statistically significant and viable experiment to give ~3k LaBr3-LaBr3 coincidences for measuring the lifetime of the 4+ state with the centroid shift method, ~4 days of beam time is required.

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Count Rate estimate: Example below gives time spectrum for < 900 LaBr 3 -LaBr 3 coincident events (half-life of yrast 2 + state in 152 Sm of 1.4 ns).

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Additional slides

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N/Z compound nano and microsecond isomers on gated 198 Pt+ 136 Xe with GAMMASPHERE+CHICO DIC Valiente-Dobon et al., Phys. Rev. C69 (2004)

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