New methodologies and techniques for 234 Th analysis Future Applications of 234 Th in Aquatic Ecosystems Woods Hole, August 2004

New methodologies and techniques for 234Th analysis

Future Applications of 234Th in Aquatic Ecosystems

Woods Hole, August 2004

Talk outline

•Classical techniques•New developments•Marine vs Fresh water•Alternative approaches, Automation•Calculation of deficiency•Outlook

followed by ion exchange separationBhat et al., 1969 Anderson and Fleer, 1982

alfa230Th

beta234Th

filtration Ion exchange

platingFe(OH)3

precipitation

U/Th separation230Th spike

digestion

Fe(OH)3 precipitation

Diss

Part

Moore and Reid, 1973

Isotope ratios Bacon and Anderson, 1982 234Th yield tracer

MnO2 impregnated fibre

acrylic

polypropylene

In-situ pumpsTwo cartridges Mann et al., 1984 in series Livingston and Cochran, 1987 all Th,Ra,Ac,

transuranics

•Ashing•leaching

Efficiency = 1 –

MnB____

MnA

Soxhlet leaching

Hanfland et al.

Non-destructive techniquesBuesseler et al., 1992

MnO2 impregnated acrylic fibre

Gamma detector efficiency (63 keV)

Melt/crush

5.3 %

Gamma count

< 1 %

ash

16.1 %

Gamma branching ratio:

63 keV 93 keV3.8 % 5.4 %

technique Fe(OH)3 precipitation

ion exchange

MnO2 cartridges

ion exchange

MnO2 cartridges

non-destructive

gamma counting

references Bhat et al., 1969 Anderson and Fleer, 1982

Moore and Reid, 1973

Mann et al., 1984

Livingston and Cochran 1987

Buesseler et al., 1992

+++

reliable

well-defined

no interferences

Spin-off of multi-tracer studies

No chemical treatments

- - -

lengthy procedure,

digestion and ion-

exchange on board

(1988 Polarstern)

Large volumes

Ship time

ashing /leaching

Needs same

cartridge efficiency

Large volumes

Ship time

Needs same cartridge efficiency

234Th techniques by 1992

Betacounting

234Th

filtration

MnO2

precipitation

U/Th separationno spike

no digestion

second filtrationDiss

Part

Mn7+ + Mn2+ MnO2

MnO2 precipitationdirect beta counting

2MnO4- + 3Mn2+ + 2H2O 5MnO2 + 4H+

RvdL & Moore, 1999

deep water calibration

0,94

0,96

0,98

1,00

1,02

1,04

1,06

1,08

St3-3 St3-3 St3-3 St6-4 St7-5 St7-5 St9-2 St9-2

station number ANT XVIII/2 PS 58/

effici

ency

deep water calibration

0,94

0,96

0,98

1,00

1,02

1,04

1,06

1,08

151

153

154-

1

156-

1

157-

1

158-

1

169-

1

185

194-

1

194-

3

station number ANT XVI/3 PS53/

effici

ency

SD 3.2 % SD 2.4 %

Precision

Deep-water calibration of 20-L method

accuracy

On-board

Duplicate 20-L samples, acidified and stored 6 months before analysis

Surface water samples

Small-volume techniques

20-L is too much for a Rosette cast

Counting statistics are not limiting

Reduction to 5, 4 and 2 liter versions

process Sample size (kg)

Counting technique SD(%)

1-counting error

N

NELHA-600m

Mn ppt 20 direct beta 9.8 2.6 18


Mn cart 550 gamma 10.9 3.5 7

Fe ppt 20 direct beta 15.5 3.9 6

Fe ppt 20 Chemistry-beta 5.1 4.1 2

HOT-3500m


Southern Ocean >250m



Comparison of techniques for total 234Th

Buesseler et al., 2001

10-L Fe(OH)3 ppt229Th + 232Th

Coppola et al., 2002

4-L MnO2 ppt230Th + 229Th

Pike et al. 2004Savoye et al. 2004

Return of the yield tracer

234Th (mBq l-1)

0 10 20 30 40 50

0.8 1.2 1.6 2.0 2.4 2.8

234Th (mBq l-1)

0 10 20 30 40

depth

(m

)

0

20

40

60

80

100

120

140

160

234Th (dpm l-1)0.0 0.8 1.2 1.6 2.0 2.4 2.8

234Th (dpm l-1) 234Th (dpm l-1)

Polar Star2/17/02

Polar Star2/19/02

Melville1/25/02

0.8 1.2 1.6 2.0 2.4 2.8

234Th (mBq l-1)

0 10 20 30 40

234Th uncorrected

234Th corrected

238U Pike et al. 2004

uncorrectedyield-corrected

Small-volume techniques

Still to be worked out:

RvdL & Moore 1999

20-L

Buesseler et al. 2001

5-L

Benitez- Nelson et al. 2001

2-L

Pike et al., 2004

4-L

MnO2 concentration

(mg/L)

1 0.2 0.1 0.25

reaction time

(hour)

8 1 8-12 12

Problems specific to direct beta measurements

High self-absorption of thick sources

Interference by other beta emitters

Beta detector

source with self-absorption

I(L) = I(0) . (1-e-L)/L

0

L

Z(cm)

absorber 30 mg/cm2

I(L) = I(0) . e-L

absorber

I = I(0)

Correction required for variable LBut: (234Th) >> (234mPa)

__>eliminate234Th betascorrect only for (234mPa)

238U

234Th

234mPa

234U

0.27 MeV

2.19 MeV

Thick beta sources

Beta detector

source with self-absorption

absorber 30 mg/cm2

Decayed source with self-absorption

absorber 30 mg/cm2

Step 1: measure filter

Step 2: repeat after decay

Step 3: measure spike

Decayed source with self-absorption

Beta detector

Step 4: measure L by sample

always use absorber to stop weak betas

Determination of self-absorption coefficient

Thick filter measuring procedure

Element Americium-241-series Thorium-232-series Uranium-238-series Uranium-235-series

AmericiumAm-241 432.6y

Plutonium

NeptuniumNp-237 2,14*1

UraniumU-233

1.592*1U-238 4,5*10

U-234 24550

U-235 7.0*10

ProtactiniumPa-233 27.0d

Pa-234 1.2min

Pa-231 32800y

ThoriumTh-229 7340y

Th-232 1.4*10

Th-228 1.91 y

Th-234 24.1 d

Th-230 75400

Th-231 25.5 h

Th-227 18.7d

ActiniumAc-225 10,0d

Ac-228 6.1h

Ac-227 21.8 y

RadiumRa-225 14,8d

Ra-228 5.75 y

Ra-224 3.7 d

Ra-226 1600 y

Ra-223 11.4d

FranciumFr-221 4,9min

RadonRn-220 55.6s

Rn-222 3.8d

Rn-219 3.96s

AstatineAt-217 32,3m

PoloniumPo-213 4,2µs

Po-216 0.15s

Po-212 45.1m

Po-218 3.1min

Po-214 0.00014

Po -210 1.38d

Po-215 1.78m

Po-211 36m

BismuthBi-213 45,59

Bi-209 stable

Bi-212 9m

Bi-214 19.9min

Bi-210 5.0d

Bi-211 2.17m

LeadPb-209 3,253h

Pb-212 10.64h

Pb-208 stable

Pb-214 26.8mi

Pb-210 22.3y

Pb-206 stable

Pb-211 25.2s

Pb-207 stable

SPIKES Th-232 U-238 U-235

2.3 MeV2.1 MeV

2.3 MeV1.0 MeV

3.3 MeV1.1 MeV

1.4 MeV

6.8 MeV1.4 MeV

alfa

beta

Beta energies > 1.0 MeVLowMediumHigh

Decay mode Particlereactivity

2.3 MeV

0.27 MeV

Interference by other betas

Interference of 226Ra daughters

Benitez-Nelson et al., 2001

•recount after 234Th decay

•background in open ocean samples approx. 4%

•222Rn vented from counter

Low 234ThHigh particle loads – thick filtersNo equilibrium at depthOther interferences (232Th series)Humics, Colloids

MnO2 ppt /direct beta method of limited value

Coastal and fresh waters

200-L method for fresh water

Waples et al., 2003

Interference of other Th isotopes

Total Th beta count Th-234Th-230 + Th-232Th-228Th-229

Cerenkov radiation

Cerenkov threshold for betas : 0.256 MeV

225 photons are produced for every cm

When v >c_

n

Cerenkov photons produced

Emax

(MeV)

Activity(Bq m-3)

Max # of photons per electron

234Th 0.27 41 2

234mPa 2.27 41 23840K 1.31 12000 130

214Bi 3.27 up to 3.3 368

Probability distribution of # of photons produced per decay of 40K

Cerenkov

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 50 100 150 200

Channel

Counts

/10

min

ute

s

distilled water

3 kBq 234Th (net)

4.6 kBq KCl (net) x 3

4.6 kBq KCl (net)

Separation of 40K and 234Th by photon number

P M T A P M T B

D ew ar flask

d is tilled w a te r

234T h sp ike

PMT A

PMT B

Semipermeable sheet

Semipermeable sheet

glass beaker

teflon cylinder

aluminum foil

Mylar foil Spike

Coincidence counting

0 # of photons 15

200

0

234Th

40K

40K x 3

coun

trat

e (c

pm)

Distribution of # of photons per event

Too low optical yield

Moore, 1990

Ideas for automation

2004

automation

AWI and ISITEC

Claudia asked:

What is the best way to convert these measurements into integrated 234Th deficiencies?

Can we assess and reduce the uncertainty in making this conversion?

Integrated deficiency

Discussion initiated by Moran et al., 2003

Integrated deficiency

1. Depth of integration• Bottom of mixed layer?• Depth of equilibrium?• Depth of sediment trap?• Depth of export calculation

2. Integration method• Sampling integration (yo-yo) • Trapezoidal integration

Current best methodsDeficiency Particulate

Open Ocean

Small-volume•ev. Spike•automation

Large-volume-filtration + gamma

20-L + beta (note interferences)

size-fractionation +

Fresh water 200-L, Waples et al., 2003

coastal Depends on salinity, particle loads, humics

summary

•Direct beta counting simplifies 234Th analysis in seawater

for better precision: yield measurement at home

•Thick sources: corrections required for self absorption

•Fresh waters and sediment samples: large contribution from other beta emitters

Outlook

•Surface waters: Continuous transects in surface waters on ships of opportunity

•High-resolution profiles should allow to make full budget in water column + surface sediment

•Parallel collection of size-fractionated particulate fraction for determination of X/234Th ratio in exported material

ID type process Sample size (kg)

Counting technique

SD(%)

1-counting

error

N

NELHA-600m

20-L filtrate Mn ppt 20 direct beta-up 7.3 2.8 17

20-L filtrate Mn ppt 20 direct beta-down 7.0 2.8 20

2-L filtrate Mn ppt 2 direct beta 5.3 3.9 8

Fe ppt filtrate Fe ppt 20 direct beta 13.8 4.9 3

20-L total Mn ppt 20 direct beta 9.8 2.6 18

2-L total Mn ppt 2 direct beta 5.6 3.4 4

Mn cart total Mn cart 550 gamma 10.9 3.5 7

Fe ppt total Fe ppt 20 direct beta 15.5 3.9 6

Fe ppt total Fe ppt 20 Chemistry-beta 5.1 4.1 2

Particles > 1 um Nuclepore 20 direct beta 21.4 4.8 18

Particles > 1 um Nuclepore 20 Chemistry-beta 7.9 4.2 3

HOT-3500m

2-L Total Mn ppt 2 direct beta 7.4 3.0 26

Southern Ocean >250m



Station 18270°13'S 6°11'W

0,0

00

0,2

00

0,4

00

0,6

00

0,8

00

1,0

00

1,2

00

0200

400

600

de

pth

(m)

234Th/238U ratio

Station 18567°S 0°E

0,0

00

0,2

00

0,4

00

0,6

00

0,8

00

1,0

00

1,2

00

0200

400

600

de

pth

(m)

234Th/238U ratio

Station 16960°S 18°30'E

0,0

0,2

0,4

0,6

0,8

1,0

1,2

0200

400

600

de

pth

(m)

234Th/238U ratio

Trapezoidal integration

Other beta emitters

Emax

(MeV)234Th 0.27

234mPa 2.27214Pb 1.02214Bi 3.27210Pb 0.06210Bi 1.16

238U series 235U series232Th series

Emax

(MeV)231Th 0.39227Ac 0.045211Pb 1.37211Bi 6.75

Emax

(MeV)228Ra 0.05228Ac 2.13212Pb 0.57212Bi 2.25

= v/c

cos = 1/ n

Cerenkov radiation

P M T A P M T B

D ew ar flask

d is tilled w a te r

234T h sp ike

PMT A

PMT B

Semipermeable sheet

Semipermeable sheet

glass beaker

teflon cylinder

aluminum foil

Mylar foil Spike

Coincidence counting set-up

Documents

New methodologies and techniques for 234 Th analysis Future Applications of 234 Th in Aquatic Ecosystems Woods Hole, August 2004