Accelerator mass spectrometry analyses ofultra-trace radionuclides in the environment- application to geosciences studies Aya SAKAGUCHI
University of Tsukuba

Special Thanks
Rosmarie Eigl
Tomoya Nomura
Minami AbeAkihisa NakajimaPeter Steier
Karin Hain
Akihiko Yokoyama
Robin Golser
Tsuyoshi Watanabe
Maki Honda
Kimikazu Sasa
Tomoeki Nakakuki
Keiichi Sasaki
Yoshio Takahashi
Akane Yamakawa
Hiroya Yamano
Members of Sueki-Lab.
Members of Yokoyama-Lab.
Members of Watanabe-Lab.
Tsukuba AMS group
Innovation Plaza Staff
R/V Hakuho-maru Crew

Hiroshima UniversityHiroshima University
University of Tsukuba
University of Tsukuba
University of Vienna
University of Vienna
Kanazawa University
University of Vienna
Hokkaido University
Japan Atomic Energy Agency
University of Tsukuba
Hiroshima University
Kanazawa Gakuin University
The University of Tokyo
National Institute for Environmental Science
National Institute for Environmental Science
University of Tsukuba
Kanazawa University
Hokkaido University
University of Tsukuba
Hiroshima University

Measurement of Environmental Radionuclides
Radiation Spectrometry
g-ray, x-ray

Mass Spectrometry

Ge Semiconductor

ICP-MSb-ray
Gas Flow Counter
Liquid Scintillation Counter

a-ray

TIMS

thermofisher.com/order/catalog/product/IQLAAEGAASFAFYMAMV#/IQLAAEGAASFAFYMAMVSIMSDetector

Si Semiconductor
Electrodeposition

Vacuumchamber

Short～Long Half-life

https://www.cameca.jp/product/sims/ims1300-hr3/

Long/Medium Half-life

Accelerator Mass Spectrometer
Discriminate the target isotope (ion)by specific combination of

M: Mass number
E: Energy
q: Charge
6MV Tandem Accelerator University of Tsukuba

Analysing Magnet
Electrostatic Analyser
Tandem Accelerator
Ionisation Chamber

5m

Long Half-life Anthropogenic Radionuclides

Classical way, but still higher potential
Applications to Environmentaldynamics tracers

Nuclear chemistry＊Material cycles in ocean, atmosphere, land

Concentration, distribution anddynamics of nuclides are importantaround reprocessing plants,
Fukushima and Chernobyl＊Development of analyticalmethod＊Spike production

Environmental
Radionuclides＊Behavior and metabolisms ofplants and animals＊Monitoring＊Analog use of short half-life nuclides
Applications of difficult to trace elements (Zr, Hf,Nb, Ta, Ge, Si) in the environment

Availability of ‘classical’ method to modern
environmental science

High feasibility usage

Non-destructive analysis
for analogous research

Essential to mass
spectrometry•Many kinds of nuclides (elements)•Specific half-lives•Wide range of concentrations•Chain nuclides•Different isotopic compositions•Introduction histories/amounts areclear in each system

Chemical separations and mass
spectrometry of 233U, 182Hf, 79Se, 135Cs,
Actinides, etc.

＊Imaging techniques and state analyses
Existence state, together with concentration
analysis, reveals a different aspect from that ofstable isotopes.

Usage of medium half-life nuclides
Possible to measure ultra-low levelsof environmental nuclides＊ Break out from ‘Earth’Science
Application to cosmic
chemistry/physicsApplication to meteorites, SK-Gdsamples, etc.

＊Unlimited possibility for g analysis
using destructive samples
The initial samples from Fukushima should havealso been subjected to ‘destructive’ γ-ray analysis.

＊Avoid extinction ofenvironmental a analysis
Nobody will be able to conduct a analysis

Radiation measurements
Real ‘ultra-trace’!

Study of Application of Anthropogenic
Radionuclides to GeoscienceOceanic Circulation Tracers
137Cs (T =30.2 y)
1/2
・dissolved metal （alkali metal）
・well known origin⇒Global-fallout
Cs-137 concentration depth anddensity distributions at N24o

Ultra-low level of 137Cs indeep water: 0.2 mBq/kg
cf. Fukushima nearshore(April/2011): 180 Bq/kg

MRI: http://www.mri-jma.go.jp/Dep/ge/ge_report/2011Artifi_Radio_report/Chapter2.html

Global Fallout - Atmospheric Nuclear Testing
Global Fallout: Nuclear contamination of theentire Earth with anthropogenic radionuclides
from atmospheric nuclear testing
137Cs in rainwater (Japan)

MRI, Japan

137Cs Measurements in Seawater

LLRL, Kanazawa Univ.
Ogoya undergroundlaboratory

Background is less than
1/200 compared withnormal detectors.
50-2000 keV 1.8 cpm←Cs2PtCl6
Aoyama, Personal comn.

New Oceanic Circulation Tracers: U-236 & U-233
233, 236U have long half-lives(1.592×107 y, 2.37×107 y) cf. 137Cs (30.2 y)Uranium is a conservative(soluble) element in seawater→233,236U in seawater can betransported with water-mass(Christl et al. 2012; Sakaguchi et al., 2012)

5-liter sample of seawater (subattograms of U) is enough for
AMS measurements (Eigl et al. 2016;Hain et al., 2020)

Anthropogenic radionuclides→Clear origin and age ofintroduction to the earth’s surface(Sakaguchi et al., 2009; Winkler et al., 2012, Hain et al., 2020)

Simple concentration method→Available on-board ship
(Abe et al., in prep)

Global-fallout(GF)
Nuclear reprocessing
plants, dumping(specific areas), etc.
233, 236U
in the environment

GF 240Pu daughters(negligibly small)

Atmospheric
Nuclear Tests

Natural nuclear reactions(negligibly small)

Production of 233U and 236U
235U(n, g)236U
235U(n, 3n)233U

238U(n, 3n)236U

232Th(n, g)233Th → 233Pa → 233U

Reconstruction of 236U Ocean Input
The 236U/238U ratio in surface seawater can be reconstructedusing coral core samples
maximum deposition in 1964
(same variation as fission-produced Cs-137)

Sampling point（Winkler et al., 2012)

Reconstructed 236U/238U ratio in Caribbean
surface seawater using a coral core

New Concentration Technique for U in Seawater
Amidoxime Adsorbents• Produced by ‘tea-bag’Amidoxime group• radiation graft polymerization• Concentrate U by acoordination
complexation withamidoxime group• Easy to handle (fabric-like)

Carbonate U

2 cmElectron beam irradiation‘Teabag’ adsorbent!

Seko et al., (2004); Tamada et al. (2007); Abe et al. in prep.

Concentrate U onboard shipSurface Currents in the Japan sea
1. Semi-closed system
2. Warm/cold current areas
3. Deep water formation
4. Shorter circulation time (100-200 y)

Liman, North-Korea currents
Counter-clockwise current
around Japan basin
Deep waterformation zone?

Tsushima, East-Korea currents
Branch of Kuroshio current(North Equatorial current)Coral Core Samples, Kume
sampling point
sampling date

N 26o 19’7.5”
E 126o 45’58.9”

speciesJul. 2014
Genus Poriteswater depth
core φtotal length

3m
5 cm
109 cmKume Island

https://upload.wikimedia.org/wikipedia/commons/3/35/East_China_Sea.PNG

Results
I feel cold,cold, cold, cold
COLD!

Yea, we did it!

236U/238U in Surface Seawater, Kume
Maximum (1954)

236U/238U(10-9)

12

Second maximum (1958)

84

Increased
steeply from1952

Small broad enhancement (1964)

01930

1950

1970
Age (year)

1990

2010

Nomura et al., 2016

236U Input to the NWP from the PPG
W130°

W160°

JapanSeaJapan
Chang
Jian R.

PacificOcean

N30°

N30°

TaiwanPhilippine

N10°500 km

PacificProving
PPG
Ground

N10°

Pacific Proving Ground Nuclear Testing

1952 - Operation Ivy

Year
1946
1948
1952
1954
1956
1958
1963

1954 - Operation CastleOperation
Area
No. of Test Yield (Mt)
Crossroads
Bikini
20.05
Sandstone
Eniwetok
30.1
Ivy
Eniwetok2
10.9
CastleEniwetok, Bikini
648.2
Redwing
Eniwetok
1720.82
Hardtack I Eniwetok, Bikini
3535.6(2000)
Dominic
Kiritmati
36 ANSCEAR36.9

1958 - Operation Hardtack

First hydrogen bomb test(1952)
Maximum explosion
yield (1954)
Second largest explosion
yield (1958)

https://ja.wikipedia.org/wiki/%E3%82%A2%E3%82%A4%E3%83%93%E3%83%BC%E4%BD%9C%E6%88%A6#/media/%E3%83%95%E3%82%A1%E3%82%A4%E3%83%AB:IvyMike2.jpg
https://ja.wikipedia.org/wiki/%E3%82%AD%E3%83%A3%E3%83%83%E3%82%B9%E3%83%AB%E4%BD%9C%E6%88%A6#/media/%E3%83%95%E3%82%A1%E3%82%A4%E3%83%AB:Castle_Romeo.jpg
https://ja.wikipedia.org/wiki/%E3%83%8F%E3%83%BC%E3%83%89%E3%82%BF%E3%83%83%E3%82%AF%E4%BD%9C%E6%88%A6#/media/%E3%83%95%E3%82%A1%E3%82%A4%E3%83%AB:HardtackOak.JPG

236U/238U in Surface Seawater, Kume
Operation Castle, 1954

Explosive yield [Mt]236U/238U

10408630GF

Operation Ivy, 1952

2042010Operation Hardtack, 1958

1946 1948 1950 1952 1954 1956 1958 1960 1962
Year
236U/238U variation coincides well with

explosion yield observed at PPG

0Fission
Explosion
yield
Yield
[Mt]
[Mt]

236U/238U [10-9]1250

233U/238U in Surface Seawater, Kume
15

2015

1010550233U/238U

236U/238U(10-9)

233U/236U(10-11)

236U/238U0Year
233U/238U ratios are 2 orders of magnitude smaller thanthose of 236U/238U. However, the basic variations are thesame for these ratios.
Nomura et al., 2016; Hain et al., 2020

233U/236U in Surface Seawater, Kume4233U/236U(10-2)

(I)

(II)

(III)

32

10

1950

1955

1960

1965

1970

Year
(I) Lower average ratio (0.31±0.07)×10-2 compared withthe other periods

Hain et al., 2020

Diffusion Simulation (FVM)
Finite Volume Method (FVM)① simple system ② physical parameters can be retained

Surface layer (150 m)
Diffusion coefficient x10

Reconstructed 236U concentration from Kume island
was used as input parameter for the very top layer
236U concentration in each layer at each time

Cj(t +δt)= Cj(t) + dt [{kj+1/2( Cj+1(t)－Cj(t) )－ kj-1/2( Cj(t)－Cj-1(t))}/dz2-λCj(t)]150 layers（CR34: 30layers）

Cj(t) : 236U (atoms/kg) in the j-th FV (j=1–150) at time tδt : time-step interval (s) [1/75 year, 16000 steps]
Kj+1/2 : vertical diffusion coefficient (cm2/s) for turbulent flow
between the j- and (j+1)-th FVs（m2/s）

λ: decay constant of 236U（1/s）

Sea Floor

236U Diffusion Simulation
236U （×106 atom/kg）
00

51015500

Depth（m）
深度（m）

1000
1500
2000
2500
3000

CR34

CR41

CR47

CR2

7.2±3.7×10-4 (m2/s)

5.5±0.5×10-4

5.6±0.7×10-4

5.0±0.5×10-4

3500
4000

0051015500
1000
1500
2000
2500
3000
3500
4000

CR17CR58

CR66

4.0±0.4×10-4
236U concentration :3.4±0.7×10-4

4.6±0.3×10-4

Fitting line :Sea Floor :Google236U in the North Atlantic Ocean• High inventories due to influence fromnuclear reprocessing plants inSellafield (UK) and La Hague (France)• High 236U/ 238U ratios at the bottom ofnorthern stations (subduction of surfacewater)(Casacuberta et al., 2014)

236U in the North Pacific Ocean• High 236U in the surface layer due
to global-fallout• Lower 236U inventory than Atlantic• 236U is retained at the surface• Quite uniform distribution
patterns among sampling points

236U in the West Pacific Ocean• High 236U in the sub-surface layerof the mid-North Pacific• One order of 236U concentrationdifference between north and south
Pacific→Very low 236U inventory inthe southern South PacificSummary 1• Very low concentrations of 233,236U have beensuccessfully measured using small volume marine
samples• Variations in 236U/238U and 233U/238U atomic ratios
and their concentrations in Northwest Pacificsurface water were reconstructed• Japan Sea water column 236U depth profiles
could be simulated using constructed values
for 236U in the surface seawater.
• Combining U isotopes with other nuclides, suchas 237Np and 135Cs, has further potential toclarify the origin of water masses
Further detailed observations are necessary.

Challenging Themes with AMS-237Np
237Np has a long half-life(2.144×106 y)

Global-fallout(GF)

Seawater samples of a few liters(attograms of 237Np) are enoughfor AMS measurements

Nuclear reprocessing
plants, etc.

cf. 1800 L for a spectrometry (Holm etal., 1987)

Np is a conservative (soluble)
element in seawater (Runde&Goff,2005) → 237Np in seawater can betransported with water-masses
Anthropogenic radionuclides→Reconstructable origin and ageof introduction to the earth’s
238U(n,2n)237U→237Np
surface

237Npin the environment Atmospheric

Nuclear Tests
GF 241Am daughters(negligibly small)

Natural nuclear reactions(negligibly small)

Important nuclides from the aspects ofradiation protection and environmental
research.
HOWEVER…there are very few
comprehensive studies and little data on
Np concentrations and distributions in theenvironment.

Np Chemical Separation Problems
Conventional (classic) method

Complicated Np purification method
Combination of solvent extractions (2 times) andanion exchange resins (3 times)Np AMS
Measurement
Problems
Problems
in Np
measurements
by AMS
Appropriate yield tracer?

236Np (Table to be agood spike for 237Np measurements
51/2=1.54x10 y)

236Np spike does not exist

Production of a Np Spike for AMS
Ideal nuclear reaction
232Th (7Li, 3n) 236gNp

High energy Li beamLong half-life Np

RIKEN
AVF Cyclotron

Interference sidereactions

7Li2+232Th (7Li, 3n) 236mNp
232Th (7Li, 2n) 237Np

232Th

236m,gNp

Production of a Np Spike for AMS
Simulation of Excitation Function by EMPIRE2・Production ratio among nuclides are different throughthe bombing energy
・ Larger 236gNp and less 236m,237Np
・No excitation functions exist for these reactions

Preliminarily Results

Before chemical separation

We were able to confirm the production 236mNp!

After chemical separation34

To Be Continued!
Th stack target preparation

We plan to distribute the Np spikefor use in mass spectrometry(can also be used for ICP-MS)

Irradiated sample

Challenging Themes with AMS-135Cs
135Cs has a long half-life(2.3×106 y)cf. 137Cs (30.2 y)

Cs is a conservative (soluble)
element in seawater
Anthropogenic radionuclides(Fission product)→the same origin as 137Cs

Potential as an alternative environmental
dynamic tracer to short half-life 137Cs
D.C. Snyder (2012), B.C. Russell (2014, ), V.F. Taylor (2008), L. Pibida (2004),
M. Granet (2008) and 6 of others

135Cs Analysis?
Why AMS(AMS)
なぜ加速器質量分析か？
Severe interference with some elements
135, 137Cs/q

Environment
135Cs/133Cs = 10-11 – 10-7

135, 137Ba+, 95Mo40Ar+, 97Mo40Ar+ etc.

Instruments

135Cs/133Cs

SF-ICP-MS

10-6 – 10-5

Thermo Element 2XRICP-MS/MS<10-810-14 (Theoretical)
Agilent 8800

ICP-CRC-MS 10-10
TIMS

10-10 – 10-9

RIMS

10-10 – 10-8

AMS

10-15

Perkin Elmer DRCII(Theoretical)

ILIAMS
133Cs+

6 × 10-12

VERA ILIAMS (3MV)

B.C. Russell et al. (2015), J. Zheng et al. (2013), V.F. Taylor et al. (2008), T. Lee et al.
(1993), W. Bu et al. (2019), L.R. Karam et al. (2002), L. Pibida et al. (2004), J.
Eliades et al. (2013)

Ion Laser InterAction Mass Spectrometry- ILIAMSHe

135Ba+

https://isotopenphysik.univie.ac.at/fileadmin/user_upload/p_isotopenphysik/images_AMS_at_VERA/VERA_20170720.jpg

Chemical Separation Method for 135Cs
Zheng et al. (2014; 2016) constructed a brilliant
chemical separation method for ICP-QQQ-MS

HOWEVER . . .
it is still necessary tochemically separate Ba
for AMS analyses
Measurement of 135Cs with
ICP-QQQ-MS

Summary 2• New chemical separation methods andimproved AMS system enable the measurementof ultra-low level medium half-life radionuclides inthe environment• Clarification of environmental dynamics can beachieved from these studies by combiningmeasurements and analyses of exotic nuclides(not only from the viewpoint of radiologicalprotection)• Global efforts should be made to develop thisstudy field