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An AGATA @ GANIL Proposal P.H.Regan 1,10 , J.Nyberg 2 , J.Simpson 3 ,

Precision Determinations of the Transition Quadrupole Moments Approaching the N p N n Valence Maximum: Lifetimes of Yrast States in 166,168 Dy. An AGATA @ GANIL Proposal P.H.Regan 1,10 , J.Nyberg 2 , J.Simpson 3 ,

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An AGATA @ GANIL Proposal P.H.Regan 1,10 , J.Nyberg 2 , J.Simpson 3 ,

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  1. Precision Determinations of the Transition Quadrupole Moments Approaching the NpNn Valence Maximum:Lifetimes of Yrast States in 166,168Dy An AGATA @ GANIL Proposal P.H.Regan1,10, J.Nyberg2, J.Simpson3, J.J.Valiente Dobon4, P. John5, A.Atac6, B.Cederwall6, A.Gengelbach2 , P.A.Soederstroem7, Zs. Podolyak1, N.Marginean8 , J.Ljungvall9 , P.M.Walker1, W.N.Catford1, G.Lotay1,10, S.M.Judge10 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

  2. What underlies nuclear quadrupole deformation? 166Dy100 166Dy100: Does the B(E2:2+→ 0+) (a) increase as the valence maximum is reached at N=104 ? or (b) reduce compared to 164Dy98 (the heaviest stable isotope) as the E(2+) systematics suggest?

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

  4. Nuclear structure information. The ‘reduced matrix element’ , B(lL) tells us the overlap between the initial and final nuclear single-particle wavefunctions. (trivial) gamma-ray energy dependence of transition rate, goes as. Eg2L+1 e.g., Eg5 for E2s for example. Transition probability (i.e., 1/mean lifetime as measured for state which decays by EM radiation) Reminder:How is measuring the lifetime useful?

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

  6. 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) 044307 We can populate high-spin physics in neutron rich nuclei using binary collisions/multi-nucleon transfer. Modified from Introductory Nuclear Physics, Hodgson, Gadioli and GadioliErba, Oxford Press (2000) p509

  7. 166,168Dy yrast states populated with CLARA+PRISMA experiment, gated on binary BLFs (Kr isotopes) to select Dy partners following the 82Se+170Er DIC / binary transfer reaction.

  8. 166,168Dy yrast states populated with CLARA+PRISMA experiment, gated on binary BLFs (Kr isotopes) to select Dy partners following the 82Se+170Er DIC / binary transfer reaction.

  9. Proposed Experiment • 136Xe beam on a thick 170Er target with a thick 197Au backing to • stop the reaction residues. • Emitted gammas from binary partner nuclei detected in a combined • AGATA + 32 element LaBr3 detection array. • AGATA to select 166,168Dy channels by (stopped) in-beam gates on • higher-lying transitions in 166,168Dy (from Ip=6+ and above) and • also from isomeric decays in the barium binary partner nuclei, • e.g., Ip=10+ isomer in 136Ba. • LaBr3-LaBr3 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.

  10. 136Xe beam on a ‘thin’ 198Pt target (850 MeV); GAMMASPHERE + CHICO. BLF stopped in view of GAMMASPHERE detectors.

  11. 136Xe+198Pt CHICO + GAMMASPHERE data J.J. Valiente-Dobon PhD thesis Surrey (2003) 194Os enhanced! Clearly identify 184-196Os in binary partner channels via the 2p transfer; range from x=2 to 14 neutrons evaporated. We might expect a similar population in 170-xDy isotopes following 136Xe+170Er reaction.

  12. Combined AGATA Demonstrator and FATIMA Array 32 LaBr3 detectors 1.5” diameter x 2” long in 2 rings of 16 detectors; with the AGATA demonstrator.

  13. Tests with 152Eu source to measure lifetime of Ip=2+ 122 keV level in 152Sm. T1/2 = 1.4ns

  14. 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.

  15. Count Rate estimate: Example below gives time spectrum for < 900 LaBr3-LaBr3 coincident events (half-life of yrast 2+ state in 152Sm of 1.4 ns).

  16. Additional slides

  17. Valiente-Dobon et al., Phys. Rev. C69 (2004) 024316 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 84 83 82 81 80 79 78 77 nano and microsecond isomers on gated 198Pt+136Xe with GAMMASPHERE+CHICO DIC 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 76 75 74 73 59 58 57 56 55 54 53 52 51 50 N/Z compound

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