Moving along z 82 beyond the doubly magic 208 pb nucleus
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Moving along Z=82, beyond the doubly-magic 208 Pb nucleus. G.Benzoni INFN sezione di Milano. Outline: physics motivations reaction mechanism experimental details data analysis Selection of nuclei of interest preliminary results and comparison with shell model calculations. 208 Pb.

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Moving along Z=82, beyond the doubly-magic 208 Pb nucleus

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Moving along z 82 beyond the doubly magic 208 pb nucleus

Moving along Z=82, beyond the doubly-magic 208Pb nucleus

G.Benzoni

INFN sezione di Milano

  • Outline:

  • physics motivations

  • reaction mechanism

  • experimental details

  • data analysis

    • Selection of nuclei of interest

  • preliminary results and comparison with shell model calculations


Moving along z 82 beyond the doubly magic 208 pb nucleus

208Pb

N/Z~1.0– 1.6

N/Z~3.0

Study shell structure along Z=82

What is the shell structure of neutron-rich Pb nuclei?

Evolution of shell structure: Measurement of the E(2+), E(4+) and B(E2)


Moving along z 82 beyond the doubly magic 208 pb nucleus

Search for exotic Pb isotopes “east of 208Pb”

stable

Excited states

Isomeric states

Need to test stability of shell structure N=126, Z=82 region

Indications of a weakening of Z=82 when approaching drip-line

Drip-line is far away and not at all possible to approach

TAG: long-living isomeric states


Moving along z 82 beyond the doubly magic 208 pb nucleus

What can isomers tell us?!

ns Years

T1/2(isomer) is “long” decay is hindered

EXPERIMENTAL:

  • mere existence!

  • properties: E*, I(ħ), T1/2

  • decay mode(s)

  • intermediate levels: E*, Iħ, lifetimes,...

    THEORY:

  • single-particle energies

  • configurations

  • interaction strengths

  • deformation

  • ...

  • “FUTURE”:

  • Coulomb excitation of isomers

  • interaction cross section gives radii

  • fusion-evaporation using isomeric beams


Moving along z 82 beyond the doubly magic 208 pb nucleus

Search for exotic Pb isotopes “east of 208Pb”

Up to date information on heavy Pb following Pfutzner exp. @ GSI:

Populated up to 215Pb but g infos only on 212Pb

Predicted Presence of isomers involving high-j orbitals νg9/2, νi11/2, νj15/2

GSI

  • 5x106 pps

  • 2 HPGe detectors (Effγ=1%)

  • 350 ions implanted

Neutron-rich lead isotopes known up to 212Pb

M. Pfutzner PLB444 (1998) 32.


Moving along z 82 beyond the doubly magic 208 pb nucleus

Beta-decay lifetimes

  • Experimental β-decay data needed around 208Pb to validate theoretical models.

  • Predictions might differ by orders of magnitude.

  • β-lifetimes needed for r-process calculations.

  • Last lifetime measured for 215Pb

I.N. Borzov PRC67, 025802 (2003)


Moving along z 82 beyond the doubly magic 208 pb nucleus

Experimental approach:

238U fragmentation at 1 GeV/u allows to reach heavy Pb isotopes with reasonable cross section (212Pb up to 220Pb).

Epax

The GSI UNILAC-SIS accelerator system combined with the FRS and RISING setup provide a UNIQUE worldwide facility to populate and study the neutron-rich lead isotopes.

Abrabla

M. Pfutzner PLB444 (1998) 32.


Moving along z 82 beyond the doubly magic 208 pb nucleus

Ablation (evaporation)

abrasion

Production mechanism: relativistic fragmentation

pre-fragment

  • production of nuclei ranging from beam species to H

  • vfragment ≈ vbeam

  • short flight time chance to study short living nuclei

  • Cold fragmentation: fragments with N similar to the beam, but with several protons stripped


Moving along z 82 beyond the doubly magic 208 pb nucleus

Experimental details:

Experiment performed at the end of September 2009

5 days data taking

Beam current 1-2 x 109 pps (238U 1GeV/u)

3 FRS settings:

205Pb : ID confirmation

215-217Pb: “production” settings:

populated nuclei ranging from 212-218Pb

GSI-FRS

Br-DE-Br method


Moving along z 82 beyond the doubly magic 208 pb nucleus

91+

2.5 g/cm2 Be

92+

238U

90+

238U

1GeV/u

212Pb

Deg. S1: 2.4 g/cm2

S2 position

MONOCHROMATIC

Deg S2: 758 mg/cm2

Experimental details:

charge states of primary beam

(A/Q)212Pb == (A/Q)238U

Intermediate focal plane.

Mocadi simulation

(cross section not included)

E215Pb= 650 MeV/u after S1 deg


Moving along z 82 beyond the doubly magic 208 pb nucleus

Active Stopper

9 DSSSD 5cm x 5cm

2TPC [XS4]

SCI41[TOF]

2x MUSIC [Z1,Z2]

Deg S4: ~2.4 g/cm2

2TPC [XS2]

SCI21 [TOF]

15 Cluster (105 HPGe crystals)

εg = 9-14% (1.3-0.6 MeV)

Flash mult. = 4-5 crystals dead

Experimental details:

RISING stopped beam array

FRS detectors

SCI42 implantation

SCI43 veto

238U

1GeV/u


Moving along z 82 beyond the doubly magic 208 pb nucleus

RISING Stopped Beam set-up

24

12


Moving along z 82 beyond the doubly magic 208 pb nucleus

start

Veto

The active stopper

Active stopper: 3x3 DSSSD

5cm x 5cm

Logarithmic preamplifiers

– position

– implantation-decay correlation

– energy (implantation/decay)

Implant GeV scale

Beta decay MeV scale

Implantation-gamma correlation for isomers:

Implantation trigger

Beta-gamma correlation for implanted nuclei:

Beta-decay trigger


Moving along z 82 beyond the doubly magic 208 pb nucleus

Z

Heavy products

Pb

Fission fragments

A/Q

Where is 215Pb ???

Fission fragments+high Z products  ID very complicated


Moving along z 82 beyond the doubly magic 208 pb nucleus

215Pb_sett

DQ=-1

DQ=0

DQ=-2

Z

DQ=+1

Br1 - Br2

Charge state selection

  • Formation of many charge states owing to interactions with materials

  • Isotope identification is complicated

  • Need to disentangle nuclei that change their charge state after S2 deg.

    (Br)Ta-S2 – (Br)S2-S4


Moving along z 82 beyond the doubly magic 208 pb nucleus

DQ=0

Z

Br1 - Br2

Pb

Application of charge state selection

Z

A/Q

Z

Clear ID plot, well resolved

A/Q


Moving along z 82 beyond the doubly magic 208 pb nucleus

206Hg

209Tl

212Pb

215Bi

210Hg

213Tl

216Pb

219Bi

215Pb setting with DQ=0, g information for:

Z

A/Q


Moving along z 82 beyond the doubly magic 208 pb nucleus

Isomers in ms range found in all measured even Pbs, 212-218Pb

Example of Eg vs. Time matrix to identify long-living isomers

214Pb

Energy (keV)

Projection on Energy axis

PRELIMINARY

185

339

Time (25 ns)

834

Energy (keV)


Moving along z 82 beyond the doubly magic 208 pb nucleus

Preliminary results: Pb chain

T1/2 = 5.0 (3) μs

212Pb

6+ -> 4+: 160 keV

4+ -> 2+: 312 keV

2+ -> 0+: 805 keV

T1/2 = 5.9 (1) μs

214Pb

4+ -> 2+: 341 keV

6+ -> 4+: 170 keV

2+ -> 0+: 834 keV

T1/2=0.40 (1) μs

216Pb

6+ -> 4+: 160 keV

4+ -> 2+: 401 keV

2+ -> 0+: 887 keV


Moving along z 82 beyond the doubly magic 208 pb nucleus

6+ -> 4+:

160 keV

T1/2 = 5.0 (3) μs

4+ -> 2+: 312 keV

2+ -> 0+:

805 keV

212Pb comparison btw us and M.Pfutzner...

narrower slits to cut primary beam and heavier nuclei (increased beam intensity)

Higher g efficieny (~10%)

Number of isotopes ~ 100

Number of isotopes:350

PRELIMINARY


Moving along z 82 beyond the doubly magic 208 pb nucleus

X

8+

8+

X

The experimental levels and the seniority scheme

The 8+ isomer is a seniority isomer, involving neutrons in the 2g9/2

216Pb

212Pb

214Pb

210Pb


Moving along z 82 beyond the doubly magic 208 pb nucleus

S.p. energies (MeV)

N=184

Shells

-1.40

3d3/2

-1.45

2g7/2

4s1/2

-1.90

3d5/2

-2.37

-2.51

1j15/2

N=7 major shell

-3.16

1i11/2

2g9/2

-3.94

N=126

The valence space in the Kuo-Herling interaction

208Pb is a doubly-magic nucleus (Z=82, N=126).

For neutron-rich Lead isotopes, the N=6 major shell is involved

PRC 43, 602 (1992)


Moving along z 82 beyond the doubly magic 208 pb nucleus

Shell model calculations with K-H

Calculations with Antoine code and K-H interaction

218Pb

216Pb

210Pb

212Pb

214Pb

th.

exp.

th.

exp.

th.

exp

th.

exp.

th.


Moving along z 82 beyond the doubly magic 208 pb nucleus

210Hg isomer

208Hg

PRC 80, 061302(R)

Change in structure ?

Preliminar!

210Hg

642 keV

663 keV

546 keV

Energy (keV)


Moving along z 82 beyond the doubly magic 208 pb nucleus

  • Resume:

  • recente exp. to study heay Pb isotopes with 238U fragmentation reactions

  • preliminary results on Pb chain up to 216Pb

  • Preliminary comparison with shell model calculations confirming 8+ isomer is a seniority isomers

  • Still to do

  • study other charge states

  • detailed study of isomers in species (Hg, Tl, Bi,Po)

  • study short/long living isomers with other TDC signals

  • extract isomeric ratios

  • study beta decay

  • ......... (suggestions ???)


Moving along z 82 beyond the doubly magic 208 pb nucleus

Collaboration: ~70 people and 18 institutions

G. Benzoni, J.J. Valiente-Dobon, A. Gottardo,R. Nicolini.

A. Bracco, F.C.L. Crespi,F. Camera, A. Corsi, S. Leoni, B. Million, O. Wieland, G.de Angelis, D.R. Napoli, E. Sahin,S.Lunardi,R.Menegazzo, D. Mengoni, F. Recchia, P. Boutachkov, L. Cortes, C. Domingo-Prado,F. Farinon, H. Geissel, J. Gerl,N. Goel, M. Gorska, J. Grebosz, E. Gregor, T.Haberman,I. Kojouharov, N. Kurz, C. Nociforo, S. Pietri, A. Prochazka, W.Prokopowicz, H. Schaffner,A. Sharma, H. Weick, H-J.Wollersheim, A.M. Bruce, A.M. Denis Bacelar, A. Algora,A. Gadea, M. Pf¨utzner, Zs. Podolyak, N. Al-Dahan, N. Alkhomashi, M. Bowry, M. Bunce,A. Deo, G.F. Farrelly, M.W. Reed, P.H. Regan, T.P.D. Swan, P.M. Walker, K. Eppinger,S. Klupp, K. Steger, J. Alcantara Nunez, Y. Ayyad, J. Benlliure, E. Casarejos,R. Janik,B. Sitar, P. Strmen, I. Szarka, M. Doncel, S.Mandal, D. Siwal, F. Naqvi,T. Pissulla,D. Rudolph,R. Hoischen,P.R.P. Allegro, R.V.Ribas,Zs. Dombradi

Universita’ degli Studi e INFN sezione di Milano, Milano, I;

INFN-LNL, Legnaro (Pd), I;

Universita’ di Padova e INFN sezione di Padova, Padova, I;

University of the West of Scotland, Paisley, UK;

GSI, Darmstadt, D;

Univ. Of Brighton, Brighton, UK;

IFIC, Valencia, E;

University of Warsaw, Warsaw, Pl;

Universiy of Surrey, Guildford, UK;

TU Munich, Munich, D;

University of Santiago de Compostela, Santiago de Compostela, E;

Comenius University, Bratislava, Sk;

Univ. Of Salamanca, Salamanca, E;

Univ. of Delhi, Delhi, IND;

IKP Koeln, Koeln, D;

Lund University, Lund, S;

Univ. Of Sao Paulo, Sao Paulo, Br;

ATOMKI, Debrecen, H.


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