1

Decay studies of r-process nuclei

Karl-Ludwig Kratz

- Max-Planck-Institut für Chemie, Mainz, Germany- Department of Physics, Univ. of Notre Dame, USA

T1/2P

n

Sn

n

HRIBF 2006

2

-2

0

2

4

6

8

10

12

14

16

38 40 42 44 46 48

Mass number

scaled theoretical solar r-processscaled solar r-process

Nb

Zr

Y

SrMo

Ru

Rh

Pd

Ag

Ba

La

Ce

Pr

Nd

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

Hf

Os

Ir

Pt

Au

Pb

ThU

GaGe

CdSn

Elemental abundances in UMP halo stars

r-process observables

Solar system isotopic abundances, Nr,

“FUN-anomalies” in meteoritic samples

isotopiccomposition Ca, Ti, Cr, Zr, Mo, Ru, Nd, Sm, Dy ↷ r-enhanced

Historically,nuclear astrophysics has always been concerned with• interpretation of the origin of the chemical elements from astrophysical and cosmochemical observations • description in terms of specific nucleosynthesis processes (already B²FH, 1957).

[‰

]

ALLENDE INCLUSIONEK-1-4-1

Mass number

CS 22892-052 abundances

T9=1.35; nn=1020 - 1028

R-process observables

, Bi

3

Nuclear-data needs for the classical r-process

nuclear masses

Sn-values r-process pathQ, Sn-values theoretical -decay properties, n-capture rates

-decay properties

neutron capture rates

fission modes

T1/2 r-process progenitor abundances, Nr,prog

Pn smoothing Nr,prog Nr,final (Nr,)

RC +DC smoothing Nr,prog during freeze-out

SF, df, n- and -induced fission “fission (re-) cycling”; r-chronometers

-decayfreeze-out

nuclear structure development

- level systematics- “understanding” -decay properties- short-range extrapolation into unknown regions

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History and progress in measuring r-process nuclei

Definition: r-process isotopes lying in the process path at freeze-out ↷ when r-process falls out of (n,)-(,n) equilibrium

even-neutron isotopes ↷ “waiting points” important nuclear-physics property T1/2

odd-neutron isotopes ↷ connecting the waiting points important nuclear-physics property Sn n.

In 1986 a new r-process astrophysics era started: at the ISOL facilities OSIRIS, TRISTAN and SC-ISOLDE T1/2 of N=50 “waiting-point” isotope 80Zn50 (top of A80 Nr, peak; “weak” r-process)

T1/2 of N=82 “waiting-point” isotope 130Cd82 (top of A130 Nr, peak; “main” r-process)

In 2006, altogether more than 50 r-process nuclei have been measured, which lie in the process path at freeze-out.

These r-process isotopes range from 68Fe to 139Sb.

The large majority of these exotic nuclei was identified at CERN/ISOLDEvia the decay mode of

–delayed neutron emission.

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What we knew already in 1986 ...

K.-L. Kratz et al (Z. Physik A325; 1986)

Exp. at old SC-ISOLDEwith plasma ion-source quartz transfer lineand dn counting

Problems:high background from

-surface ionized 130In, 130Cs-molecular ions [40Ca90Br]+

Request: SELECTIVITY !

Shell-model (QRPA; Nilsson/BCS) prediction

1.0

T1/2(GT) = 0.3 s

4.11+

2.0

g7/2, g9/2

Q = 8.0 MeV

1+

1+

1+

1+

1+

1+

1+

0

1.0

3.0

4.0

5.0

6.0

1-

IKM

z –

15

5R

(19

86

)

T1/2 = 230 ms

T1/2 = (195 ± 35) ms

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The r-process “waiting-point“ nucleus 130Cd

Q

7.0 8.9

2.9

2QP

4QP

J=1+

{g7/2, g9/2}

Sn

T1/2, Q, E(1+), I(1+), log ft

1.2

...obtain a physically consistent picture!

“free choice” of combinations:

low E(1+) with low Q

high E(1+) with low Q

low E(1+) with high Q

high E(1+) with high Q

T1/2(GT) 233 ms1130 ms 76 ms 246 ms

(log ft=4.1)

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Ag Cd In CsSn Sb Te I Xe

Improvements since 1993 atPS-Booster ISOLDE

• Fast UCx target• Neutron converter• Laser ion-source• Hyperfine splitting• Isobar separation• Repeller• Chemical separation• Multi-coincidence setup

Request: Selectivity !

50 800 >105

the Ag “needle” in the Cs “haystack”

Why ?

How?

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Request: Selectivity !

Laser ion-source (RILIS)

Chemically selective,three-step laser ionisationof Cd into continuum

130Cd1669 keV

130Cd 1732 keV

Laser ON

Laser OFF

130Sb1749 keV

Energy [keV]

-singles spectrum

Laser ON

Laser OFF

Comparison of Laser ON to Laser OFF spectra

Properties of the laser system:Efficiency ≈ 10%Selectivity ≈ 103

5s2 1S0

5s 5p 1P1

5s 5d 1D2 510.6nm

643.8nm

228.8nm

Cd

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Mass scan at HRS (ISOLDE) in 2002;efficiency corrected

in reality, „on a good day…“M/M ≈ 1/4000

M/M=7.5*10-5

HRS design≥ 1/104

Request: Selectivity !Isobar separation

In

Cs Cd

Cd 2.000

In 17.000

with HRS!

10

0

10

20

30

40

50

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53

distance / cm

acti

vit

y / %

Zn Rb Ag In Cd Cs

Request: Selectivity !

Chemistry in the transfer line between target and ion-source ↷ thermochromatography

Deposition of Zn, Rb, Ag, In, Cd and Cs in a quartz tube with a temperature gradient

separation Cd, from Cs, In

Prototype UCx target at CERN/ISOLDE with

temperature-controlledquartz transfer-line

Oct. 2005

Diploma thesis C. Jost (2005)

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Surprises

• high [g7/2g9/2] 1+ state

• weakening of the g7/2 - g9/2

residual interaction

• high Q-value

130In81

OXBASH(B.A. Brown, Oct. 2003)

01-

4733+

1382 (old)1+

1+

8950-

14411-

19061-

251525981-

0-

2181 (new)reduction of

the TBME (1+) by 800 keV

Full spectroscopy 130Cd decay

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42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82Fe

CoNi

CuZn

GaGe

AsSe

BrKr

Rb

SrY

ZrNb

MoTc

RuRh

PdAg

CdIn

Sn

Z N

SbTe

IXe

CsBa

82 84 86 88 90 92 94

Snapshots: r-process paths for different neutron densities

heaviest isotopes with measured T1/2

g9/2 d5/2 s1/2 g7/2 d3/2 h11/2

g9/2

p1/2

p3/2

f5/2

f7/2

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42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82Fe

CoNi

CuZn

GaGe

AsSe

BrKr

Rb

SrY

ZrNb

MoTc

RuRh

PdAg

CdIn

Sn

Z N

SbTe

IXe

CsBa

82 84 86 88 90 92 94

R-process path for nn=1020

„waiting-point“ isotopes at nn=1020 freeze-out

nn=1020

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42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82Fe

CoNi

CuZn

GaGe

AsSe

BrKr

Rb

SrY

ZrNb

MoTc

RuRh

PdAg

CdIn

Sn

Z N

SbTe

IXe

CsBa

82 84 86 88 90 92 94

„waiting-point“ isotopes at nn=1023 freeze-out

R-process paths for nn=1020 and 1023

(T1/2 exp. : 28Ni – 31Ga, 36Kr, 37Rb,47Ag – 51Sb)

nn=1023

nn=1020

15

42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82Fe

CoNi

CuZn

GaGe

AsSe

BrKr

Rb

SrY

ZrNb

MoTc

RuRh

PdAg

CdIn

Sn

Z N

SbTe

IXe

CsBa

82 84 86 88 90 92 94

(T1/2 exp. : 28Ni, 29Cu, 47Ag – 50Sn)

R-process boulevardboulevard for nn=1020, 1023 and 1026

„waiting-point“ isotopes at nn=1026 freeze-out

nn=1023

nn=1026

nn=1020

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... resulting from new experimental and theoretical nuclear structure information:

• better understanding of shape of and matter flow through the major r-process

bottle-neck at the A130 Nr, peak

• no justification to question waiting-point concept

(Langanke et al., PRL 83, 199; Nucl. Phys. News 10, 2000)

• no need to request sizeable effects from -induced reactions

(Qian et al., PRC 55, 1997)

Astrophysical consequences

r-process abundances in the Solar System and in UMP Halo stars... ...are governed by nuclear structure!

Nuclear masses from

AMDC, 2003

ETFSI-Q

Normalized to Nr, (130Te)

Longer T1/2!

„short“ T1/2 „long“ T1/2

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Abundance clues and constraints

• Observations versus calculations - solar system

- UMP halo stars

• Conditions for „main“ and „weak“ r-process - n-densities - entropies

• Split between the two r-processes - 129I (Wasserburg et al.) - below N=82

• R-process chronometric pairs - Th/Eu, Th/U - new: Th/Hf

• Ages of UMP stars, Galaxy and Universe

• Suggestions on r-process sites

• Galactic chemical evolution

• (Un-) importance of fission recycling

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Conclusion

nuclear-physics data

for explosive nucleosynthesis calculations still unsatisfactory !

better global models

for all nuclear shapes(spherical, prolate, oblate, triaxial, tetrahedral,…)

and all nuclear types(even-even, odd-particle, odd-odd)

more measurements

masses !gross -decay propertieslevel systematicsfull spectroscopy of selected key“ waiting-point isotopes

Despite impressive experimental and theoretical progress, situation of

with sufficiently large SP model space,