Measuring regional scale distribution of radiocaesium

Measuring regional scale distribution of radiocaesium

David SandersonScottish Universities Environmental Research Centre

East Kilbride, Glasgow G75 0QF, UK

Caesium workshop : Fukushima recovery – understanding, modelling and managing radioacaesium decontamination, CORASSE, Fukushima, Japan

September 30 – October 3rd 2013

OutlineOutline

• Airborne and mobile gamma spectrometry

• Measurement technologies and small footprint systems

• Mapping radiocaesium (UK and European examples)

• Spatial resolution and reproducibility at regional and local scales

• International validation and ground to air comparisons

• Work conducted in Japan in 2012/13

• Future opportunities and needs

Airborne & Mobile Gamma Spectrometry for mapping radioactivity

Airborne & Mobile Gamma Spectrometry for mapping radioactivity

・ AGS is capable of rapid radiometric mapping of large areas Sensitive gamma-ray detector mounted on aircraft High volume NaI (or combined NaI/Ge system) Low altitude survey flights (30-100m) Large survey areas, high sampling density ~1000’s of observations per hour 104-105 m2 fields of view

・ Mobile Gamma spectrometry Geocoded gamma spectrometry operated from

backpacks, small vehicle, UAV’s, boats, hovercraft etc

More confined field of view – suited to detailed surveys of eg urban areas

Data capture rate 102 -103 per hour 10-102 m2 fields of view

・ AGS system used in ECCOMAGS Exercise ・ Fully validated performance

17 spectral input channels, multi-sensor capable High volume NaI arrays, HPGe detectors Stabilised power supply Upgraded (2005/6) to more powerful computers, larger

displays, revised power systems Software upgrades (2008-2010)

• ERS Format spectral input/output

HPGe analysis• Full spectral regridding

• Disjoint spectral windows

・ Real time mapping with differential “rainbow plots”・ Alarms

• Gross & stripped count rate

• Significance from differential analysis

• Intelligent digital filtering

・ 5Hz, EGNOS enabled GPS

SUERC AGS multispectrometer

SUERC AGS multispectrometer

・ Increased data throughput

Resolution maintained in high radiation fields (but could use HPGe)

・ (But summing multi-compton losses in detector arrays)

Digital SystemsDigital Systems

NaI

(Tl)

cp

s

0

200

400

600

800

HP

Ge

cps

0

2

4

6

8

10

12

・ Simple, compact systems

・ Self contained HV supply and DSP chips

・ USB connectivity

・ Ideally suited to weight limited platforms

・ Alternative detector geometries?

Digital systems have advantages

Belgoprocess Site 2Belgoprocess Site 2

BR3

201.2 201.4 201.6

400m0 200

201.0

212.0

200.8200.6

212.2

211.8

212.8

213.0

212.4

212.6

Calibration based on infiniteplanar source geometry

Measurement centre

BR3

201.2 201.4 201.6

400m0 200

201.0

212.0

200.8200.6

212.2

211.8

212.8

213.0

212.4

212.6

Measurement centre

BR3

201.2 201.4 201.6

400m0 200

201.0

212.0

200.8200.6

212.2

211.8

212.8

213.0

212.4

212.6

Calibration based on infiniteplanar source geometry

Measurement centre

・137Cs, 60Co activity from stored materials

・214Bi activity from 222Rn discharges from stored uranium & radium

GM

X C

ou

nt

rate

(cp

s)

0.1

1

10

NaI

(Tl)

Co

un

t R

ate

(cp

s)

1

10

100

1000

Energy (keV)

0 500 1000 1500 2000 2500 3000

0.1

1

10

1

10

100

1000

South of site

North of site

13

7C

s

60C

o

21

4B

i

13

7C

s

60C

o6

0C

o6

0C

o

・NaI Spectra show spectral distortion and coincidence summing

Backpack SystemBackpack System

March 2000 AGS June 2010 Backpack

Avril Weir and Catherine Mitchell survey the Scottish Enterprise Technology Park, in 2009 for their MPhysproject

“Demonstrating lightweight gamma spectrometry systems in urban environments”, Journal of environmental radioactivity, 2013, 124, 22-28

High resolution survey of Irish Sea beach in 2010

“Evaluating airborne and ground based gamma spectrometry methods for detecting particulate radioactivity in the environment: A case study of Irish Sea beaches” Science of the Total Environment 437 (2012) 285–296

3x3” NaI(Tl), digiBASE™, netbook, EGNOS enabled GPS

Regional scale mapping following the Chernobyl accident on 28th April 1986

Chernobyl 28th April 1986Chernobyl 28th April 1986

・ 28th April Chernobyl

・ UK fallout arrives early May

・ Initial deposition estimates based on limited ground sampling and meteorological modelling

・ Early SURRC surveys – SW Scotland, Western Isles, West Cumbria, North Wales

・ Later repeat surveys show long term migration of radionuclides

1988 MAFF Survey West Cumbria

2001 DETR study “Spatial andTemporal Aspects of airborne gammaspectrometry

Sanderson D.C.W., Scott E.M.,1989, Aerial Radiometric Survey In West Cumbria In 1988, MAFF Report N611 120

Sanderson D.C.W., Cresswell A.J., White, D.C., Murphy, S., McLeod J. 2001, Investigation of Spatial and Temporal Aspects of Airborne Gamma Spectrometry. DETR Report DETR/RAS/01.001.

West Cumbria – Changes Between 1988 and 2000 - Livestock restriction

zone

West Cumbria – Changes Between 1988 and 2000 - Livestock restriction

zone

・ Total activity in area agrees to within 3% after decay correction・ Movement of activity from high to lower lying ground due to hydrological and colluvial

processes

1988 1988(decay corrected)

June 2000

Total Area (TBq) 9.35±0.02 7.01±0.02 7.22±0.02

Black Combe (GBq) 496±3 372±3 319±1

Corney Fell (GBq) 704±3 528±3 469±2

Loweswater Fell (GBq) 636±3 477±3 453±1

Lowlands (GBq) 851±16 638±12 732±8

Investigation of Spatial and Temporal Aspects of Airborne Gamma

Spectrometry

Investigation of Spatial and Temporal Aspects of Airborne Gamma

Spectrometry

Analysis of line spacing and environmental change

How reproducible is AGS?

How to measure change

D

A

Tielines

B

C

F

G

H

I

Barrow-in-Furness

Windermere

Windermere

ConistonWater

Carlisle

Wigton

RockcliffeMarsh

Annan

Allerbeck

Chapelcross

BassenthaiteLake

EnnerdaleWater

DerwentWater

Croasdale

Keswick

Cockermouth

Millom

DuddonEstuary

Moricambe

Silloth

Solway Firth

Sellafield

Ravenglass

WastWater

Caerlaverock

Workington

Maryport

St BeesHead

Whitehaven

5020 30 40

0 10 20km

3 000m1000

80

29

90

2 000m704 000m

80

40

50

60

70

00

10

20

30

5 000m

Geographic overlays reproducedfrom Ordnance Survey Strategi data with the permission of The Controller of Her Majesty's Stationary Office.(c) Crown Copyright 1998

Inner SolwayThe Solway Firth has extensive areas of salt marshContaminated by discharges from Sellafield

Survey areas6x11km, encompassing Rockcliffe and Burgh marshes and the tidal inlets of the Esk and the Eden30x20km, including Annan, Silloth and part of Carlisle

Survey dates and flight linesApril 1999: 50 and 250m line spacings ; June 2000: 250m line spacing, February 1992: 500m line spacing

West CumbriaUpland areas and coastal plainContaminated by Chernobyl and Windscale fire

Survey areasCoastline and Sellafield area (March 2000)40x40km (500m), northern Lakes and lower lying areas (June 2000)50x50km (2.5km), Lake District high ground (June 2000)Older data : Aug/Sept 1988: 500m line spacing; Sept 1990: Sellafield area

Inner Solway 137Cs Distributionand the landcover setting

Inner Solway 137Cs Distributionand the landcover setting

Hought

Harker

Sc

Blackford

Westlinton

Todhills

Moorhouse

Grinsdale

on-EdenKingstown

Cargo

Rockcliffe

Thurstonfield

Burgh by Sands

Kirkandrews

Beaumont

GretnaRigg

lasson

Drumburgh

astriggs

ort Carlisle

0 1 2km

36 37 38

3 0

00

m

32 33 34 3530 312928

66

65

64

63

62

61

60

59

26 27

3 0

00

m2

5

5 000m

5 000m67

58

Geographic overlays reproduced from Ordnance Survey Strategi data with the permission of The Controller of Her Majesty's Stationary Office.(c) Crown Copyright 1998

RockcliffeMarsh

Burgh Marsh

Sparse data for West Cumbria

Sparse data for West Cumbria

Barrow-in-Furness

Windermere

ConistonWater

Windermere

Wigton

Croasdale

EnnerdaleWater

DerwentWater

BassenthaiteLake

Silloth

Sellafield

Millom

Ravenglass

DuddonEstuary

WastWater

Workington

Whitehaven

Maryport

St BeesHead

40

0 10 20km

5010 20 303 000m90 0070

80

90

00

2 000m

4 000m

5 000m

40

10

20

30

50

Geographic overlays reproducedfrom Ordnance Survey Strategi data with the permission of The Controller of Her Majesty's Stationary Office.(c) Crown Copyright 1998

Barrow-in-Furness

Windermere

ConistonWater

Windermere

Wigton

Croasdale

EnnerdaleWater

DerwentWater

BassenthaiteLake

Silloth

Sellafield

Millom

Ravenglass

DuddonEstuary

WastWater

Workington

Whitehaven

Maryport

St BeesHead

40

0 10 20km

5010 20 303 000m

90 0070

80

90

00

2 000m

4 000m

5 000m

40

10

20

30

50

Geographic overlays reproducedfrom Ordnance Survey Strategi data with the permission of The Controller of Her Majesty's Stationary Office.(c) Crown Copyright 1998

137Cs Activity for Areas C and D

137Cs Activity for Areas C and D

L in e S p a c in g (k m )

0 .0 2 .5 5 .0 7 .5 1 0 .0 1 2 .5

To

tal A

cti

vity

(T

Bq

)

3 4

3 5

3 6

3 7

3 8

3 9

4 0

4 1

L in e S p a c in g (k m )

0 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0 6 0 0 0

To

tal A

cti

vity

(T

Bq

)

1 4

1 5

1 6

1 7

1 8W e s t C u m b ria

(a re a s C + D )N o rth W e s t C u m b ria

(a re a C )Inventories of large features relative to line spacing are robust (shapes less so)

for dimensions perpendicular to lines >2x line spacing

smaller features subject to significant uncertainties for wider line spacing

Even 10km line spacings show broad distribution pattern and inventory of Chernobyl derived activity on uplands

Sanderson, D. C. W., Cresswell, A. J. and White, D. C. (2008) 'The effect of flight line spacing on radioactivity inventory and spatial feature characteristics of airborne gamma-ray spectrometry data', International Journal of Remote Sensing, 1 – 16 DOI: 10.1080/01431160701268970

ECCOMAGSECCOMAGS

・ Protocols for dose rate and radionuclide deposition mapping using AGS

・ Exercise design documentation

・ Unique data base of airborne & ground based measurements

・ Exercise report – 387p book published

・ Journal articles

・ European Capability for AGS Radiation Protection Dosimetry

・ Vol. 73, Nos 1–4, pp. 213–218 (1997)

・ European Bibliography Journal of Environmental Radioactivity

・ 53 (2001) 411-422

・ International validation of deposition and dose rate determination under conditions of cooperative trials Radiation Protection Dosimetry (2004), Vol. 109, Nos 1-2, pp. 119-125

Exercise Aims and Outcomes

Exercise Aims and Outcomes

・ Aims Validation of AGS protocols for deposition

and dose rate quantification Traceable comparisons between AGS, in-

situ spectrometry, field dose rate measurements and laboratory analysis of core samples

Demonstration of composite mapping capability

・ Venue SW Scotland May 24th-June 3rd 2002 Pre-characterisation fieldwork in

November 2001・ Organisation

International steering Committee (ISC) National Organising Committee, (NOC)

Design and Evaluation Group (DEG)

Outcomes

Participants150 participants from 18 institutions in 10 countriesObservers and visitors

Activities and achievementsAGS >120,000 measurements in common areas and composite mapping zones~150 In-situ and field dose rate measurements from calibration sites and 42 common area sites>750 laboratory gamma spectrometry results from ~130 core samples and reference materialsCGS data from 3 teams

Inch Farm

WigtownMerse

CastleKennedy

Dumfries

Stranraer

Solway Firth

Dumfries and Galloway Region

0 10 20km

ECCOMAGS Exercise : Calibration Sites

137Cs : 20.8 ± 1.0 kBq m-2

Dose rate : 0.057 ± 0.003 µGy h-1

137Cs : 224.7 ± 10.9 kBq m-2

Dose rate 0.09 ± 0.01 µGy h-1

137Cs : 6.3 ± 0.35 kBq m-2

Dose rate : 0.033 ± 0.005 µGy h-1

Calibration sites

・Sampled in November 2001

・Reference values distributed to participants

・AGS hover manoevres and in-situ measurements used for data levelling

・In-situ checks for environmental change

0.1

1

10

100

Channel

0 100 200 300 400 500

Co

un

t R

ate/

Ch

ann

el (

cps)

0.1

1

10

100

<10 m

50 - 65 m

Wigtown Merse

Inch Farm

Castle Kennedy

Ground Based Data sets – Key points for ground to air comparisons

Ground Based Data sets – Key points for ground to air comparisons

・ Laboratory Gamma spectrometry Laboratory performance Different behaviours observed between

IAEA reference materials and common bulk samples

Results provide basis for ground to air comparisons

・ In-situ data Necessary to re-standardise data sets to

common mass-depth profiles Also to re-level them to the Inch Farm site Relationships between in-situ and cores

bring mass-depth into play・ Dose Rate measurements

Field instruments showed considerable differences

Dose Rates re-estimated from in-situ spectra and cores

・ CGS biased by field of view differences

1 (S

tir)

2 (S

UE

RC

)

3 (E

RC

)

4 (B

GS

)

5 (N

RP

B)

6 (C

EH

)

7 (G

C)

8 (B

fS)

9 (S

SI)

10 (

CE

A)

1 (S

tir)

3 (E

RC

)

4 (B

GS

)

5 (N

RP

B)

6 (C

EH

)

7 (G

C)

8 (B

fS)

11 (

Ris

o)

12 (

DS

TL)

Sta

nd

ard

ised

Dif

fere

nce

-15

-12

-9

-6

-3

0

3

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15WG BS1 WG BS2 IF BS1 IF BS2 CK BS1 CK BS2

Laboratory

1 (S

tir)

2 (S

UE

RC

)

3 (E

RC

)

4 (B

GS

)

5 (N

RP

B)

6 (C

EH

)

7 (G

C)

8 (B

fS)

9 (S

SI)

10 (

CE

A)

1 (S

tir)

3 (E

RC

)

4 (B

GS

)

5 (N

RP

B)

6 (C

EH

)

7 (G

C)

8 (B

fS)

11 (

Ris

o)

12 (

DS

TL)

Sta

nd

ard

ised

Dif

fere

nce

-15

-12

-9

-6

-3

0

3

6

9

12

15SOIL 6SOIL 375SL-2

137 Cs – Bulk samples

137 Cs – IAEA reference materials

Main Common area AGS findings

Main Common area AGS findings

・ All teams identify the main radiometric features

・ Data levelling between teams using single common measurement point

Applicable to emergency response

Further corrections and analysis lead to only minor changes

・ Considerable agreement between teams

Definition of spatial features

Point to point regressions

Ground to Air ComparisonsGround to Air Comparisons

・ Ground to air comparisons

Agreement is broadly consistent with the internal consistency of each data set

AGS and in-situ sensitive to depth distribution

AGS observations are consistent with ground based results

But are spatially more numerous and representative

The data sets provide a basis for protocol validation

In-situ 137Cs (kBq m-2)

0 5 10 15 20 25 30 35

AG

S 13

7C

s (k

Bq

m-2

)

0

5

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In-situ 137Cs (kBq m-2)

0 5 10 15 20 25 30 35

AG

S 13

7C

s (k

Bq

m-2

)

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In-situ 137Cs at measured mass depth (kBq m-2)

0 20 40 60 80 100 120

AG

S 1

37C

s (

kBq

m-2

)

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137Cs from cores (kBq m-2)

0 5 10 15 20 25 30 35

AG

S 1

37C

s (k

Bq

m-2

)

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137Cs from cores (kBq m-2)

0 25 50 75 100 125 150 175 200

AG

S 13

7C

s (k

Bq

m-2

)

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75

100

125

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Assuming 8.5 g cm-2 relaxation depth Assuming measured depth profile

In-situ 137Cs (kBq m-2)

0 20 40 60 80 100

AG

S 1

37C

s (

kBq

m-2

)

0

20

40

60

80

100

I JF G HC D EA B

Dumfries

Stranraer

ECCOMAGS Exercise : Composite Mapping Areas

Solway Firth

Dumfries and Galloway Region

0 10 20km

AGS Composite mapping task

・10 contiguous areas of approximately 250-270 km2

・Each presenting diverse environments from topographic and radioecological perspectives

・Allocated to individual AGS teams to demonstrate collective mapping abilities

137Cs Map with terrain model

137Cs Map with terrain model

ECCOMAGS exercise composite mapping task 200290x40 km area; 69000 spectra; data acquired in 3 days, published on-line within a

week

Airborne Gamma Spectrometry maps • US DOE team (March), MEXT/JAEA teams April

Ground clearance 300m initiallyDose rate maps, followed by apportioned Cs maps

Visits to Japan 2012/13• March 2012 – Tsukuba,

Fukushima, Exclusion zone, Prefecture research institutes, JAEA, UK Embassy, EU delegation (DS/YT)

• May 2012 – SRRCE inaugural conference Fukushima Izaka (DS)

• July 2012 Fukushima (AC, BS)• September 2012 (SF,XS) visit

AMS labs• Oct/Nov 2012 UK Nuclear Safety

workshop (FCO) (DS)• Jan 2013 Biomass investigation

Iwaki (AC DS)

7th March 2012 Road Trip

7th March 2012 Road Trip

Energy (keV)

0 500 1000 1500 2000 2500 3000

Cou

nts

/s

0.01

0.1

1

10

100

1000

10000

13

4C

s 60

5 k

eV

134C

s 7

95

keV

13

7C

s 6

62

keV

134C

s 1

365

keV

Okuma Daycare Centre 7th March 2012

Fukushima University Kanayagawa Campus

6th March 2012

Fukushima University Kanayagawa Campus

6th March 2012

Can we use this to direct remediation?

Apportionment of dose rateApportionment of dose rate

The charts show the relative proportions of dose rates due to individual nuclides • Can we use this type of information to set and evaluate targets for remediation ?

Play Park

Shrine

Conference Hotel

Conference Venue

Gamma dose rate map Iizaka 20th May 2012 Conducted during the SRRCE meeting

University of Fukushima : areas subject to remediation July 2012

University of Fukushima : 137Cs map showing remediated areas

0

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Per

cent

age

of a

rea

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15

0

5

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137Cs kBq m-2

5 5010 1000

10

20

30

All data

Un-remediated areas

Remediated areas(exc. tennis courts)

Tennis courts

University of Fukushima : Gamma dose rate showing remediated areas

Remediated areas are on average 4 times lower than untreated areas

0

5

10

Per

cent

age

of

are

a

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20

0

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Gamma Dose Rate µGy h-1

0.05 0.5 50.1 10

10

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All data

Un-remediated areas

Remediated areas(exc. tennis courts)

Tennis courts

University of Fukushima : 134Cs map showing remediated areas

0

5

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15

Per

cent

age

of a

rea

0

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10

15

0

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134Cs kBq m-2

5 501 10 1000

10

20

All data

Un-remediated areas

Remediated areas(exc. tennis courts)

Tennis courts

134Cs (kBq m-2) 137Cs (kBq m-2) Dose Rate (μGy h-1)

Remediated Unremediated Remediated Unremediated Remediated Unremediated

Mean 23.8 80.0 36.9 121.4 0.20 0.58

Std dev 21.8 34.6 32.9 51.9 0.15 0.24

Percentiles

10th 4.9 37.8 9.2 56.7 0.08 0.30

50th 17.2 76.8 27.7 117.2 0.15 0.56

90th 48.6 124.3 76.2 189.9 0.36 0.87

Analysis of the effectiveness of remediation

Remediated areas are on average 4 times lower than untreated areas

137Cs

FU Bq kg-1

101 102 103 104 105

SU

ER

C B

q k

g-1

101

102

103

104

105

Slope: 0.965 ± 0.015Intercept: 58 ± 24R2: 0.989

Calibration site at Fukushima University

• Sampled in July 2012• Tyler et al 1996,J. Environ.

Radioactivity, 33(3), 213-235.• Soil cores analysed at

Fukushima and SUERC• Relative to international

standards• Results in good agreement for

137Cs• Reference values can be used

to check dose rate and in-situ instruments and by local groups

Mean mass depth : 0.9 ± 0.1 g cm-2

137Cs 265 ± 20 kBq m-2

134Cs 165 ± 20 kBq m-2

Dose rate 1.24 ± 0.13 µGy h-1

Calibration site at Fukushima University

• Depth Profiles from 13 cores

• Above 10 g cm-2 the profiles are approximately exponential with mean mass of 0.9 g cm-2

• But do the data below 10 g cm-2 belong to the same distribution?

• Why not?• Sample handling?• Multiple components?

 

134 C

s B

q kg

-1

10

100

1000

10000

100000

Mass depth (g cm-2)

0 2 4 6 8 10 12 14

137 C

s B

q kg

-1

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1000

10000

100000

Fukushima Prefecture Fruit Tree Research Institute

Fukushima Prefecture Fruit Tree Research Institute

Do radiometric data from experimental orchards help to understand the pathways and impacts of fruit cultivation in the presence radiocaesium?

Can we use this to evaluate solutions?

Mapping in March, May, July and Nov 2012 with training

Calibration site sampled

Mass depth (g cm-2)

0 2 4 6 8 10 12 14

13

7 Cs

Bq

kg-1

10

100

1000

10000

100000

13

4C

s B

q kg

-1

10

100

1000

10000

100000

Reference Value Backpackmeasurement

134Cs kBq m-2 135 ± 20 171 ± 3137Cs kBq m-2 245 ± 30 263 ± 6

Reference value for 3rd November 2012. Mean mass depth 0.70 ± 0.05 g cm-2. Calculated from gamma spectrometry at SUERC, no comparison with FU yet.Backpack measurements calibrated to FU calibration site, mean mass depth 0.9 g cm-2.

Citrus cultivation near Mount Shinobu

July 2012

November 2012

“Yuzu” fruit from 2012 shows higher levels of radioactivity (by an order of magnitude) than apples, pears, peaches and grapes cultivated in Fukushima

Why?

IAEA Technical report 472Interception?Translocation?Root uptake?Soil immobilisation?Contamination levels?

We think that the clue lies in evergreen nature of the tree, coupled to local topography

Biomass energy harvesting and phytoremediation ?Can they be used synergistically?

FCO prosperity funded investigation with Mitsubishi Morgan Stanley, Suncare, University of Tsukuba, NNL, and input from SUERC

January 2013 fieldwork near Iwaki using a collimator to establish the proportions of total Cs radiation originating in forest canopy

Remapping following forest litter removal to determine remediation factor

Control area to account for environmental change

Cedar Deciduous

Uncollimated Collimated Reduction Uncollimated Collimated Reduction

Number 459 174 35 18

134Cs kBq m-2 25.8 ± 0.2 24.7 ± 0.2 1.1 ± 0.3 14.4 ± 0.3 13.5 ± 0.4 0.9 ± 0.5

137Cs kBq m-2 53.0 ± 0.4 53.0 ± 0.4 0.0 ± 0.6 28.7 ± 0.7 27.8 ± 0.7 0.9 ± 1.0

Dose RateµGy h-1

0.258 ± 0.001 0.253 ± 0.002 0.005 ± 0.002 0.157 ± 0.002 0.150 ± 0.003 0.007 ± 0.004

Discussion points and conclusions

• Both low and high resolution spectrometry can be used for quantitative AGS, CGS and ground based mapping of radiocaesium and gamma dose rate

• Post Chernobyl experience, and experience of measuring the footprint of nuclear sites, and the impact of discharges to the Irish sea have provided a framework for validation of methods

• AGS is well suited to detailed regional scale investigations providing low ground clearance and close line spacings are used

• Protocols and data exchange formats have been defined in EU research, and quantitative international validation studies performed

• For more detailed work ground based approaches yield greater spatial resolution, appropriate to site specific evaluations

• Last year’s visits have confirmed the utility of radiometrics as a means of targetting and evaluating remediation, and helping to understand the distribution and dynamic behaviour of radiocaesium in important urban and rural systems

• Calibration sites were sampled and analysed in two locations providing an initial basis for cross-validation of Japanese and international teams

• It is hoped that this work can be extended in the future with the aim of helping to improve confidence in the long term recovery of Fukushima