PAUL SCHERRER INSTITUT - LSC 2017lsc2017.nutech.dtu.dk/wp-content/uploads/1-Eikenberg-presentation-LSC... · Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen,

Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen, 01-05.05.2017

PAUL SCHERRER INSTITUT

Geochemical dating of a Swiss freshwater limestone cave using 230Th/234U ingrow and 226Ra-excess

decay chronometry

Jost Eikenberg, Maya Jäggi

Division for Radiation Protection and Safety

Paul Scherrer Institute, CH-5232 Villigen



Overview / Topics

Presentation of a radiochemical method for simultaneous determination of 226Ra+228Ra followed by TDCR-measurement and optimized alpha/beta-separation

Application of the chronometers 230Th/234U and 226Ra for dating sedimentary systems



relevant isotopes for quaternary limestone dating

radionuclide analytical technique

234U, (235U), 238U, 230Th, 232Th

U/TEVA separation, electro-deposition, α-spectrometry

226Ra, 228Ra filtration (RadDisc), OptiPhaseHisafe3 cocktail, LSC

210Po spontaneous deposition on silver disc, α-spectrometry



Method implementation: low level determination of 226Ra in sediments (limestone)

• Sample dissolution CaCO3 in 1 mol/liter HCl, evaporation, dilution with distilled water

• Filtration of the sample through 3 Empore RadDisc(Mn-oxide impregnated) membrane

• Elution of Ra with alkaline Na-EDTA solution• Measuring via LSC with optimized α/β-

discrimination



The triple coincidence to double coincidence ratio (TDCR) counting technique

SA M PLE

PM R

PM S

PM

T



Pulse Length Index (PLI) discrimination with HIDEX SL 300

27 38 52 72 99 135

185

252

343

466

634

861

1169

1588

2156

2927

3973

5393

7319

9934

1348

1

1829

6

0

4

8

12

16

20

24

28



α-spectrum of 226Ra with ingrowing daughters 2 h and 8 h after separation using HIDEX 300 SL LSC

Alpha

0

20

40

60

80

100

120

140

10 100 1000 10000



α-spectrum of 226Ra with ingrowing daughters obtained 6 days after separation

Alpha

0

20

40

60

80

100

120

140

160

10 100 1000 10000



β-spectrum of 228Ra with ingrowing 228Ac 1 h and 8 h after separation using HIDEX 300 SL LSC

Beta

0

5

10

15

20

25

30

35

40

45

50

1 10 100 1000



TDCR vs. Efficiency using high purity radionuclide standard solutions

0.4 0.5 0.6 0.7 0.8 0.9 1.00.4

0.5

0.6

0.7

0.8

0.9

1.0

TDCR = efficiency

226Ra

210Pb

228Ra

TDCR

efficiency



Comparison of measured 226Ra and the progeny isotopes 222Rn, 218Po and 214Po with calculated decay/ingrowth curves

0 5 10 15 20 25 300.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

222Rn+218Po+214Po: measured data

226Ra decay curve

226Ra: measured data

222Rn+218Po+214Po ingrowth curve

rela

tive

activ

ity

time after separation [d]



238U 234U

230Th

234Pa

234Th

226Ra

222Rn

218Po 214Po 210Po

210Bi

210Pb 206Pb

235U

231Pa

231Th 227Th

227Ac

223Ra

219Rn

232Th 228Th

228Ac

224Ra228Ra

220Rn

215Po

211Pb 207Pb

211Bi 212Bi

216Po 212Po

212Pb 208Pb

207Tl 208Tl

214Bi

214Pb

4.47x109y 2.45x105y

24.1d 7.54x104y

1.17min

α4.196MeV

α4.776MeV

α4.688MeV

α4.784MeV

α5.490MeV

α6.003MeV

1600y

3.825d

3.11min

19.9min

26.8min 22.3y

7.04x108y

α6.038MeV

α4.395MeV β

α5.013MeV

3.28x104y

β18.7d

21.8y

11.4d

α4.010MeV

1.41x1010y 1.91y

5.75y

α5.423MeV6.13h

β

3.66d

α5.686MeV

55.6s

α6.288MeV

β

β

β

β

1.6x10-4s

5.01d

α7.687MeV

α5.304MeV

stable

138.4dβ

β

1.06d

β

α5.716MeV

α6.819MeV

3.96s

1.8x10-3s

2.14min

36.1min stable

α7.386MeV

α6.623MeV

4.77min

β66.3%

0.15s

β β

α6.779MeV 1.01h

33.7%α

6.051MeV10.6h

3.05min

β

stable

β

α8.784MeV

3x10-7s

238U-Series 235U-Series 232Th-Series

UPaThAcRaFrRnAtPoBiPbTl



Challange for the isotope geochemist: closing the gap between the established210Pb and 230Th/234U chronometers

10-1 100 101 102 103 104 105 1060.0

0.5

1.0

1.5

2.0

210Po/210Pb

210Po/210Pb

210Pb/226Ra

210Pb/226Ra

226Ra/230Th

226Ra/230Th

230Th/234U

230Th/234U

daug

hter /

pare

nt

time after formation [y]

( ) ( )PoPbRnRaThUU 210210222226230234238 →→→→



Principles of U series dating: 1. 230Th/234U/238U

( )teUtTh 2301)0()( 234230 λ−−⋅=

)()0()( 230234234230 tt eeUtTh λλ −− −⋅=

)()0()0()( 230234230 234230230 ttt eeUeThtTh λλλ −−− −⋅+⋅=

teUtU 238)0()( 234234 λ−⋅=



Principles of U series dating: 1. 230Th/234U/238UUUU 238238234 )0()0( == ( )teUtTh 2301)0()( 234230 λ−−⋅=

0 50 100 150 200 250 3000.0

0.2

0.4

0.6

0.8

1.0

238U, 234U

230Th

rela

tive

activ

ity (n

ot to

sca

le)

time after separation [ky]



Problem 1: inherited 230Th, wrong age calculation( ) tt eTheUtTh 230230 )0(1)0()( 230234230 λλ −− ⋅+−⋅=

0 50 100 150 200 250 3000.0

0.2

0.4

0.6

0.8

1.0

230Th ingrowth + decay, with initial 230Th(0)/234U = 0.2

230Th/234U = 1

230Th ingrowth, without inherited 230Th230Th ingrowth + decay, with initial 230Th(0)/234U = 0.1

U-Th-evolution

230 Th

(t)/23

4 U ac

tivity

ratio

time after formation [ky]



U-series application with U-Th isochrones in sedimentology

0.5 1.0 1.5 2.0 2.5 3.00.5

1.0

1.5

2.0

2.5

3.0Sedimentary Systems

mixed (authigenic + detritus) phases: 230Thingrowth dating

T0

e

quip

oint

=

U/Th

ratio

of d

etrit

us c

ompo

nent

T1

U/Th mixing line at T0:authigenic phases with detritus contamination

isochroneequiline

: T > 0.3 M

y

230 Th

/ 232

Th a

ctivi

ty ra

tio (r

elat

ive s

cale

)

234U / 232Th activity ratio (relative scale)



Geological section of the aquifer / recharge area of hell grottoes springs



Travertine dating via 226Raex/234U and 230Th/234U



View into the

cave system



Travertine precipitation: thermodynamic background

OHCOOCOH 2222 +→+−+ +→→+ 33222 HCOHCOHOHCO−+−+ +↔++ 3

233 2HCOCaHCOHCaCO

HCO CO OH3 2− −↔ +

HCO CO H3 32− − +↔ +

Ca CO CaCO232

3+ −+ ↔

2 32

3 2 2HCO Ca CaCO CO H O− ++ ↔ ↓ + ↑ +



Ingrowth of 230Th without an inherited component, why that ?

3 4 5 6 7 8 91E-16

1E-14

1E-12

1E-10

1E-8

1E-6

1E-4

detection limit for 232Th, 230Th and 228Th

uraninite solubility (mildly reducing: Eh = 0.5 - 0.059pH)

thorianite solubility

conc

entra

tion

[mol

/l]

pH



226Ra/230Th/234U dating principle230 230 230 234 2300 1Th t Th e U et t( ) ( ) ( )= ⋅ + ⋅ −

− −λ λ

230

232

230

232230

234

2322300 1Th t

ThTh

The U

Thet t( ) ( ) ( )= ⋅ + ⋅ −− −λ λ 234 234 232U U k Thaut m m= − ⋅

0 100 200 300 400 5000

10

20

30

40

Fig. 8-3a

magnif

icatio

n in F

ig. 8-

3b

3800 year construction line6500 year iso

chron

present day U/Th mixing line

equil

ine

230 Th

/ 232 Th

activ

ity ra

tio

234U / 232Th activity ratio




− −λ λ

230

232

230

232230

234

2322300 1Th t

ThTh

The U

Thet t( ) ( ) ( )= ⋅ + ⋅ −− −λ λ 234 234 232U U k Thaut m m= − ⋅

0 10 20 30 40 500

1

2

3

4

Fig. 8-3b

3800 year construction line 6500 year isochron

present day U/Th mixing line

equil

ine

230 Th

/ 232 Th

activ

ity ra

tio





− −λ λ

Let‘s find an analytical (not

numerical) solution for the propagation of

the 226Ra activity with

time

0 5 10 15 200.0

0.2

0.4

0.6

0.8

1.0

226Ra(0)/234U = 0.2

226Ra(0)/234U = 0.5

226Ra(0)/234U = 1.0

230Th(t=0) = 0

234U(t) = 234U(0)23

0 Th/2

34U,

226 Ra

/234

U ac

tivity

ratio




226Ra/230Th/234U dating principle226 226 226 234 226

230230

226

226 2300 1 1Ra t Ra e U e et

t t( ) ( ) ( ) ( )

= ⋅ + ⋅⋅ − − ⋅ −

−−

− −λ

λ λλ λλ λ

226 226 226Ra t Ra Ra tex aut( ) ( )sup= − 226 226 232Ra Ra k Thaut m m= − ⋅

226

226

226 226

2260 0226Ra t

Ra

Ra Ra t

Raeex aut t( )

( )

( )

( )sup=

−= −λ t

Ra Ra t

Raage

aut= − ⋅−

10226

226 226

226λln

( )

( )sup

F tRa Ra t

Raeaut t( )

( )

( )sup=

−− −

226 226

226 0226λ



Validating the model with the sample data

0 2 4 6 8 1010-2

10-1

100

regression fit:λ = (0.444 + 0.041)10-3 y-1

T1/2 = 1560 + 150 years

17

19

6

14

129

15

16

10

8

1

11

2

18

1354

excess 226Ra decay curve226Raex(t)/

226Ra(0) = e-λ226t

226 Ra

ex /

226 Ra

(0)



PAUL SCHERRER INSTITUTCalculating 226Raex-ages analytically with the assumption of constant

Raex/234U ratios

0 2 4 6 8 100.00

0.05

0.10

0.15

0.20

19

11

6

10

151817

25

48

1216

14

9

13

1

226Ra(0)/234U initial value

230Th ingrowth 226Raex decay

230Th supported 226Ra ingrowth

226Ra(t)/234U decay + ingrowth curve

226 Ra

(t)/23

4 U ac

tivity

ratio






Reasons for a stable aqueous chemistry, i.e. constant initial 226Ra(0)

0 2 4 6 8 100.0

0.5

1.0

1.5

2.0

0.0

0.5

1.0

1.5

2.0

mean 234U/238U ratio in travertine = 1.28 + 0.06

mean Ba/Ca ratio in travertine = (0.49 + 0.02)10-3

present day 234U/238U groundwater ratio

Ba/Ca weight ratio (*10 -3)23

4 U/23

8 U ac

tivity

ratio

230Th/234U sample age [ky]



Comparing 226Raex/ 226Ra(0) with 230Th/234U ages

0 2 4 6 80

2

4

6

8

17

19

6

12

915

10

8

11

218

5

4

226Raex/226Ra(0) age = 230Th/234U age

226 Ra

ex/22

6 Ra(0

) age

[ky]

230Th/234U age [ky]



Conclusions

230Th/234U and 226Raex/234U two chronometer dating yields consistent results (agreeing ages)

Inherited 230Th at sample formation is negligible

The chemical groundwater composition seems to be highly uniform, obviously there is almost no change of the 226Ra-initial with time



Understanding the dynamics of active volcanic systems: Can we determine melt uplift velocities, melt chamber residence times

or eruption events by use of natural tracers ??



The dynamic earth: sea floor spreading and subduction of oceanic plates



Study objects: island arc volcanic rocks from the Sunda-Banda subduction zone



Which radio-tracers can be applied ?

Isotope Half-life [years] Suitable time span

230Th 76000 2000 – 200000

231Pa 33000 1000 - 100000

226Ra 1600 100 - 6000

210Pb 22 3 - 100



U-Th-Ra fractionation during melt differentiation

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.80.5

1.0

1.5

2.0

2.5

3.0Ra > U > ThRa > Th > U

IAB: (this study)alkali basalts: (ref 2)MORB: (ref 1)

226 Ra

/ 230

Th a

ctivi

ty ra

tio




Thank you for your attention

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PAUL SCHERRER INSTITUT - LSC 2017lsc2017.nutech.dtu.dk/wp-content/uploads/1-Eikenberg-presentation-LSC... · Paul Scherrer Institut • 5232 Villigen PSI LSC Int. Conference, Copenhagen,