Precision Determinations of the Transition Quadrupole Moments Approaching the NpNn Valence Maximum:

Lifetimes of Yrast States in 166,168Dy

An AGATA @ GANIL ProposalP.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, UK2 - Uppsala University, Sweden

3 - STFC Daresbury Laboratory, UK4 - INFN Legnaro, Italy5 - INFN Padova, Italy

6 – Stockholm, Sweden7 - RIKEN, Japan

8 - IFIN Bucharest, Romania9 – CSNSN Orsay, France

10 – National Physical Laboratory, UK

What underlies nuclear quadrupole deformation?

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?

166Dy100

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

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-rayenergy dependence oftransition rate, goes as. Eg

2L+1 e.g., Eg5 for E2s

for example.

Nuclear structure information. The ‘reduced matrix element’ , B(lL) tells us the overlapbetween the initial and final nuclear single-particle wavefunctions.

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.

2)12( L

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) p868Juutinen et al. Phys. Lett. 386B (1996) p80Wheldon et al. Phys. Lett. 425B (1998) p239 Cocks et al. J. Phys. G26 (2000) p23Krolas et al. Acta. Phys. Pol. B27 (1996) p493Asztalos et al. Phys. Rev. C60 (1999) 044307

CCMMAX

MAX

TB

TLF

VER

L

LAA

L

2

2

31

2

1

1

7

2

:limit Rolling

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.

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.

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.

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

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.

194Os enhanced!

136Xe+198Pt CHICO + GAMMASPHERE data J.J. Valiente-Dobon PhD thesis Surrey (2003)

Combined AGATA Demonstrator and FATIMA Array

32 LaBr3

detectors1.5” diameterx 2” longin 2 rings of16 detectors; with the AGATAdemonstrator.

T1/2 = 1.4ns

Tests with 152Eu source to measure lifetime of Ip=2+ 122 keV level in 152Sm.

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.

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).

Additional slides

67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85

59585756555453525150

757473

76

8483828180797877

N/Z compound

nano and microsecond isomerson gated 198Pt+136Xe withGAMMASPHERE+CHICODIC 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124

Valiente-Dobon et al., Phys. Rev. C69 (2004) 024316