Anthropogenic Actinides in the Environment

Stephan Winkler

stephan.winkler@univie.ac.at

Outline

• Anthropogenic Sources of Actinides

• Methods of Measurement

• Applications

• Plutonium isotopes in a Lake Erie Sediment profile

• 236U from global fall-out in a Carribean Coral Core

Reactor

Weapon

Diamond, H., P. R. Fields, et al. (1960). "Heavy Isotope Abundances in Mike Thermonuclear Device." Physical Review 119(6): 2000.

Ivy Mike

0

20

40

60

80

100

120

140

160

180

200

1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963

Yie

ld (

Mt)

year

Atmospheric Testing

USSR

USA

Plutonium

P.W. Krey, in “Transuranium Nuclides

in the Environment”

240Pu/239Pu 0.1760±0.0140

241Pu/239Pu 0.0016±0.0003 (June 2006)

242Pu/239Pu 0.0044±0.0011

~2000kg of 239Pu from the stratospheric

fall-out have been dispersed world-

wide

Production of 236U

(n,3n)

Main Production channel in thermonuclear devices is (n,3n) of 14MeV neutrons on 238U. (Sakaguchi et al)

Main Production in Reactors via (n,γ) of thermal neutrons on 235U

236U from global fall-out

236U/239Pu = 0.24±0.02

(typ.: 1012...1013 at236U/m2)

Sakaguchi et al., 2008

236U Inventory Natural:

• from 235U(n,)236U; nucleogenic or cosmogenic;

• 236U/U between 10-14 and 10-10

• ~30 kg exist in top 1000 m of earth crust

Anthropogenic:

• 106 kg were produced in nuclear reactors

• 103 kg were produced and globally dispersed in atmospheric testing => estimated oceanic 236U/U between 3·10-9 (dispersed in top 200m) and 2·10-10 (fully dispersed)

• second most abundant anthropogenic radio-nuclide

• difficult to measure

Techniques of Measurement

• Decay counting

• Thermal Ionisation Mass Spetrometry (TIMS)

• Inductively Coupled Plasma – MS (ICPMS)

• Accelerator Mass Spectrometry (AMS)

-Spectroscopy

•Mikroprecipitation with NdF3 onto membrane filter

•Elektroplating

•238Pu / 239(40)Pu

242Pu

239(40)Pu

238Pu

Liquid szintillation

• For emitter 241Pu

TIMS (thermal ionization mass spectrometry)

Re filament Triton TIMS

Pictures provided by S.

Richter, IRMM, Geel,

Begium.

ICP-MS

http://www.gvinstruments.co.uk/

IsoProbe (GV Instruments)

AMS

The Vienna Environmental Research Accelerator (VERA)

Detection efficiency and limits 239Pu

atoms/count Detection limit

AMS

(many laboratories) 104 X×104

ICP-MS

Ketterer 2008 103

Taylor et al. 2001 107 (for 10% uncertainty)

TIMS

Beasley et al. 1998 20 ~3 × 104 (“for precise ratio measurement”)

Abundance sensitivity for 236U/U true samples quoted

AMS

ANTARES Hotchkis et al. 2000 7×10-9 1×10-8

CAMS Buchholz et al. 2007 4×10-9 1×10-9

VERA Winkler et al. 2011 3×10-12 1×10-13

ANU Wilcken at al. 2008 1×10-12 1×10-13

ICP-MS

REIMEP-18 3 ×10-8

Buchholz et al. 2007 1.5 ×10-8 – 2×10-7 1.5×10-8

TIMS

Richter et al. 1999 2×10-10

Why AMS is more sensitive than MS

•Simplest conventional MS:

• Produce mono-energetic ions (fixed energy over charge, E/q)

• Separate masses with magnetic sector field (selects momentum over charge, p/q)

m/q is fixed

• High energy improves beam emittance

better ion optics

• Problems with molecular ions:

• conventional MS can hardly separate 235UH from 236U

destroy molecules in AMS during stripping

• Problems with "tails": no ion source is really mono-energetic, no separator is perfect

• Tails originate partly from interaction with residual gas

AMS increases energy to several MeV, this reduces the relevant cross sections.

• add more, redundant separators to cut off tails (also in conventional MS, e.g. WARP filter)

Applications

Ocean transport

C.-K. Kim, C.-S. Kim, B.U. Chang, S.W. Choi, C.S. Chung, G.H. Hong, K. Hirose, Y. Igarashi,

Plutonium isotopes in seas around the Korean Peninsula, Sci. Total Environ. 318 (2004)

197–209.

Relatively large sample sizes needed (3 to 500L)

S.E. Everett, S.G. Tims, G.J. Hancock, R.

Bartley, L.K. Fifield,

Comparison of Pu and 137Cs as tracers of soil

and sediment transport in a terrestrial

environment

J. Environ. Radioact. 99 (2008) 383–393.

X. Zhang and D.E. Walling. Characterizing

Land Surface Erosion from Cesium-137

Profiles in Lake and Reservoir Sediments.

J. Environ. Qual. 34 (2005) 514-523

Soil erosion and sediment transport

• Both bind readily to soil and sediment particles, but 239Pu today is 14 times more abundant.

• An AMS measurement of 239Pu from 3g processed sample takes 15 minutes (max)

239Pu v 137Cs

• Both bind readily to soil and sediment particles, but 239Pu today is 14 times more abundant.

• An AMS measurement of 239Pu from 3g processed sample takes 15 minutes (max)

• The same analysis done with 137Cs requires 100g samples and 2 days of counting!

239Pu vs. 137Cs

Nuclear Safeguards and Forensics

Characterizing Uranium Ores

• Non-anthropogenic 239Pu and 236U, although low-levels. Production via neutron capture from s.f. and (alpha,n) on light elements. Can be used to fingerprint ore bodies. (e.g. K. Wilcken, et al, 2008)

• A potential exploration tool: measurement of 236U/238U in pristine U-rich waters.

• Chemical evolution of U in rocks and soils

Plutonium Isotopes in a Lake Erie Sediment Core and Vermillion River

Range Soils

244Pu as indicator for global fallout?

Reactor

Weapon

Lake Erie Sediment Core 15

Chronology of Core 15

48.2° N, 92.5° W

Vermillion River Range Soil

The was soil collected from pockets on an exposed granite surface.

These pockets served as traps for run-off from large areas of the granite surface, thereby concentrating atmospherically deposited radionuclides over a wide area into the pockets.

While there is no stratigraphy, this offered high Pu content - 5-10Bq per processed sample. The sediment core had only ~24mBq for a 3g sample of the fall-out peak

The ANU 14UD Tandem Accelerator

Results Sample Approx.

Year

Activity

(mBq/g)

240Pu/239Pu 241Pu/239Pu

·10-3

242Pu/239Pu

·10-3

244Pu

counts

239Pu Counts

(1/10 of time

for 244Pu)

244Pu/239Pu

1 2004

(8.7±1.0)·10-5

8 1997 7.21 ± 3.66

23 1983 1.57 ± 0.50 3.99 ± 0.83

37 1972 3.48 ± 0.70 0 1158

41 1968 3.67±0.02 0.183±0.005 5.38 ± 0.72 3 2790

42 1967 4.59±0.07 0.180±0.002 4.06 ± 0.44 1 3211

43 1966 5.53±0.06 0.184±0.008 4.32 ± 0.35 2 12914

44 1965 6.60±0.08 0.189±0.006 0.89 ± 0.27 4.27 ± 0.37 11 22106

45 1964 8.50±0.28 0.182±0.006 2.58 ± 0.41 3.90 ± 0.27 38 31820

46 1963 6.17±0.02 0.158±0.002 3.50 ± 0.42 15 10400

47 1962 5.31±0.06 0.138±0.004 1.39 ± 0.35 2.52 ± 0.53 10 7448

48 1961 4.43±0.06 0.140±0.004 3.19 ± 0.69 0 934

(1.86±0.26)·10-4

49 1960 4.77±0.10 0.130±0.002 1.09 ± 0.23 2.46 ± 0.87 11 6695

50 1959 4.34±0.10 0.160±0.001 5.52 ± 0.62 1 2461

51 1958 1.18 ± 0.14 6.15 ± 0.83 40 17836

52 1957 0.39±0.03 0.154±0.035 0.77 ± 0.34 3.95 ± 0.82

53 1956 0.60 ± 0.60 1.80 ± 0.90

Results

Sample 240Pu/239Pu (ICP-MS)

244Pu/239Pu (AMS)

244Pu counts

Vermillion 1 0.188 (9.24 ± 0.55)·10−5 920

Vermillion 2 (7.59 ± 0.47)·10−5 746

Vermillion 3 0.194 (7.42 ± 0.45)·10−5 802

Mixing: 241Pu/239Pu vs 240Pu/239Pu

pre-moratorium

post-moratorium

0.0E+00

5.0E-04

1.0E-03

1.5E-03

2.0E-03

2.5E-03

3.0E-03

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40

24

1P

u/2

39P

u

240Pu/239Pu

Lake Erie

nw testing

VermillionRangefission device

"Ivy Mike"

global average (P.W. Krey)

Mixing: 242Pu/239Pu vs 240Pu/239Pu

pre-moratorium

post-moratorium

0.0E+00

5.0E-03

1.0E-02

1.5E-02

2.0E-02

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40

24

2P

u/2

39P

u

240Pu/239Pu

Lake Erie

nw testing

VermillionRange

fission device

"Ivy Mike"

global average (P.W. Krey)

Mixing: 244Pu/239Pu vs 240Pu/239Pu

pre-moratorium post- moratorium

0.0E+00

2.0E-04

4.0E-04

6.0E-04

8.0E-04

1.0E-03

1.2E-03

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40

24

4P

u/2

39P

u

240Pu/239Pu

Lake Erie

nw testing

VermillionRange

"Ivy Mike"

fission device

244Pu as indicator for global fallout?

• 244Pu is a good indicator and even allows us to distinguish USSR and USA test series, but…

244Pu as indicator for global fallout?

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

239 240 241 242 243 244 245

isotope mass number A

AP

u/2

39P

u is

oto

pic

ra

tio

Eye guide global fallout

Salzburg soil

Sellafield sea sediment

"Ivy Mike" bomb test

Sellafield upper limit

P. Steier, et al

244Pu and 241Pu

• Both can be used to distinguish global fall-out and a mixture of more recent sources

• 241Pu is easier accessible to a number of techniques and is sufficient if details of the fall-out don’t matter

• 244Pu provides a time marker within the fall-out pulse, potentially of interest to earth science studies

Measurement of 236U/238U in corals as a proxy for anthropogenic and pre-anthropogenic 236U in ocean

waters

236U as oceanic tracer

• U behaves conservatively in ocean water under oxic conditions – the residence time being ~0.5My.

• Unlike 129I or 14C, atmosphere-ocean exchange plays no role.

• There are bound to be locally distinct 236U/U signatures due to rainfall patterns and highly localized releases from reactor accidents and reprocessing plants (e.g. Sellafield)

U in Corals

• Corals build uranium into their aragonite skeletons (~3ppm)

• This uranium represents the uranium in seawater at the time of growth

• Some corals display well-defined yearly banding

U in Corals

• Corals build uranium into their aragonite skeletons (~3ppm)

• This uranium represents the uranium in seawater at the time of growth

• Some corals display well-defined yearly banding

Determine the year-by-year 236U bomb-pulse in ocean waters

Get hold of U from seawater not yet affected by anthro-pogenic 236U

U in Corals

• Corals build uranium into their aragonite skeletons (~3ppm)

• This uranium represents the uranium in seawater at the time of growth

• Some corals display well-defined yearly banding

Determine the year-by-year 236U bomb-pulse in ocean waters

Get hold of U from seawater not yet affected by anthro-pogenic 236U – very likely this is no longer possible from actual seawater today

Montastraea faveolata Colony forming species

Sample Collection

The Reef Environment

Sampling Location • Coral Core HMF-1 was collected in January 2007 at the Turneffe Atoll

(17°18'25" N, 87°48'04" W) • The depth was 19ft and the total length of the core is 112cm • It has been previously used as reference for a study on contaminant

trace elements on cores from other sites in the Carribean.

Jessica E. Carilli, et al. Marine Pollution Bulletin 58 (2009) 1835–1842

Coral Stratigraphy

Cleaning and Sample Preparation

• Removal of discoloured pieces and contamination from sawing

• 2x ultra-sonic washes in deionised bi-distilled water • For the pre-nuclear samples:

Ultrasonic wash with 30%H2O2 + 1% NaOH to hydrolyse residual organics

HNO3 clean in ultrasonic (loss of ~5% of the coral skeleton This was also done for some of nuclear-age samples, to

test for adsorbed hot particles (no evidence for that)

After cleaning corals are dissolved in HCl and co-precipitated with Fe(OH)3 followed by a standard UTEVA column extraction method.

0.0E+00

5.0E-10

1.0E-09

1.5E-09

2.0E-09

1940 1950 1960 1970 1980 1990 2000 2010

23

6U

/23

8U

year

HMF-1

0.0E+00

5.0E-10

1.0E-09

1.5E-09

2.0E-09

1940 1950 1960 1970 1980 1990 2000 2010

23

6U

/23

8U

year

HMF-1

Pre-anthropogenic 236U Samples

• Samples covering years 1943 to 1905 were measured so far (20-70µg U each)

• The lowest measured 236U/U ratio is 3.3±0.6·10-12, which is still far above expected levels

However, this was just a first test and significantly more material is available to attack this limit.

Pre-nuclear age samples

1.0E-12

1.0E-11

1.0E-10

1.0E-09

1900 1910 1920 1930 1940 1950

23

6U

/23

8U

Year

HMF-1

Detection limit for small samples

1.0E-14

1.0E-13

1.0E-12

1.0E-11

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-13 1.0E-12 1.0E-11 1.0E-10 1.0E-09 1.0E-08 1.0E-07

23

6U

/23

8U

238U5+ current

HMF-1 nuclear age

HMF-1 pre-nuclear

Vienna-KkU dilution

Procedural Blank

The Fe Carrier Problem

• Currently at least half of the background can be attributed to the Fe carrier

• Different Fe carriers were tried (Spectrosol, Goodfellow 99.99+% Fe)

• Cleaning with UTEVA improved results but there still is some U at the 3-10ppm levels left

• First test with pre-nuclear iron lacks statistics at this point for first conclusions

Limit on pre-nuclear 236U/U

• So far we can limit (90% C.L.) pre-nuclear 236U/U in the oceans as <4·10-12

• This we expected for certain beforehand

• However, from the experience in this project so far there is a good chance we improve on this limit over the next few months

236U Conclusions

• The 236U bomb-pulse seems to be well-preserved in corals.

• The response time seems to be at most 1 year - which is shorter than generally assumed

• The expected northern-southern hemisphere difference, rainfall dependent fall-out patterns, and accidental releases will make 236U an ocean tracer that may have wider application

Summary

• The tracing of anthropogenic actinides is a growing field with new application being added as techniques improve

• The potential of minor actinides and 236U is being unlocked only now

• In both areas advanced AMS systems like VERA are virtually without serious competition with regard to detection limit

Acknowledgments

Scientific Collaborators

Peter Steier

Keith Fifield

Steve Tims

Jessica Carilli

Mike Ketterer

Acknowledgments

University of Vienna

Australian National University

Northern Arizona University

Scripps Institute of Oceanography

Australian Nuclear Science and Technology organisation

Thank You for Your Attention!

stephan.winkler@univie.ac.at AMS-12, Wellington, NZ, 2011