Nuclear Instruments and Methods in Physics Research B 223–224 (2004) 87–91

www.elsevier.com/locate/nimb

Performance of the new iodine-129 beamline at JAERI-AMS

Takashi Suzuki *, Takafumi Aramaki, Toshikatsu Kitamura, Orihiko Togawa

Marine Research Laboratory, Mutsu Establishment, Japan Atomic Energy Research Institute, Mutsu, Aomori 035-0064, Japan

Abstract

Anticipating the application of 129I as an oceanographic tracer in marine environment studies in the North Pacific, a

new beamline has been set up at the AMS facility of the Japan Atomic Energy Research Institute for the measurement

of iodine isotopic ratios (129I/127I). It is demonstrated that iodine isotopic ratios can be measured with a precision below

2%, and that the detection limit is substantially better than 10�13. The method of preparing AgI sample material from

seawater is described.

� 2004 Elsevier B.V. All rights reserved.

PACS: 82.80.Ms; 07.75.+h

Keywords: Accelerator mass spectrometry; AMS; Iodine-129; Seawater; Time-of-flight; TOF

1. Introduction

A new beamline has been set up at the Accel-

erator Mass Spectrometry (AMS) facility of the

Japan Atomic Energy Research Institute (JAERI-

AMS). The AMS system, manufactured by High

Voltage Engineering Europa (HVEE), features a3 MV Tandetron and two independent beamlines

[1]. One is used for high-precision 14C-AMS [2] and

the other has been added for AMS with a variety of

other long-lived radiometric nuclides, particularly129I. In the following, we concentrate on129I-AMS

and refer to the associated system components as

the iodine beamline. In Section 2, we give an over-

view of this beamline, repeating the description and

* Corresponding author. Tel.: +81-175-28-2616; fax: +81-

175-22-4213.

E-mail address: iodine@popsvr.tokai.jaeri.go.jp (T. Suzuki).

0168-583X/$ - see front matter � 2004 Elsevier B.V. All rights reser

doi:10.1016/j.nimb.2004.04.021

the 129I/127I acceptance test given in [3]. In Section

3, we discuss the performance of this beamline

(reproducibility, precision and detection limit). In

Section 4, we present our chemistry method for the

extraction of iodine from seawater and subsequent

preparation of ion source target material. We con-

clude with a brief summary and research outlook ofour laboratory.

2. Description of the iodine line

A diagram of the JAERI-AMS system is shown

in Fig. 1. The ion source is a HVEE model 846B

Cs sputtering source for negative ions and has acarousel which can hold up to 59 target holders.

Samples are inserted and measured under com-

puter control. A combination of 54� electro-

static analyzer (calculated energy resolution: 400)

with a 90� bouncer magnet (calculated mass

ved.

TOF detector

65o ESA

115o MagnetTandem accelerator90o Bouncer Magnet

54o ESA

Ion Source

127I

129I

Start MCPCarbon foil

Stop MCP

Q-snout

Q-pole

Stripper Canal

Iodine lineCarbon line

Stop plate

Slit

Fig. 1. The whole JAERI-AMS system. Bold lines denote the new beam line which is optimized to measure iodine isotopic ratio (129I/127I). Dotted lines denote 14C beam line.

88 T. Suzuki et al. / Nucl. Instr. and Meth. in Phys. Res. B 223–224 (2004) 87–91

resolution: 400) provides mass analysis with dou-

ble-focussing properties. Injection of specific

isotope beams into the accelerator is donesequentially by high-voltage biasing the magnet

chamber. Injection times for 129I and 127I are cho-

sen to be 8 and 2 ms, respectively. A Faraday,

located on the image point of the bouncer magnet,

allow the measurement of the stable isotope (127I)

intensity during injection of the radioisotope (129I)

into the accelerator. A full description of the

Tandetron accelerator, recirculating gas stripper,and associated beam optics can be found elsewhere

[4]. The maximum terminal voltage is �3 MV. The

measurement condition at the terminal is 2.5 MV

and charge state is selected 5+ because of no in-

terferencing peak of molecular fragments [5].

In the high-energy section, mass analysis is

performed by a 115� magnet (q ¼ 1200 mm,

m=Dm ¼ 2000). The 127I current is measured by anoff-axis Faraday cup located near the magnet’s

image point. Next, a 65 � electrostatic analyzer

(ESA) (q ¼ 1700 mm, E=DE ¼ 1000) provides the

required dispersion to separate out isotopic inter-

ferences (such as charge-exchanged 127I) from 129I.

Two electrostatic quadrupole lenses, located near

the ESA’s entrance and exit, ensure proper focus-

ing into the detector.

Particle detection and identification of 129I isperformed via time-of-flight (TOF). A detailed

layout of the TOF system is shown in Fig. 2. With

each incoming ion passing through a carbon foil

(20 lg/cm2) secondary electrons are emitted. These

electrons are directed by a permanent magnet onto

a micro channel plate (MCP: Comstock model CP-

640C/50F) for the generation of the start signal.

Subsequently, the ions are stopped on a sphericalaluminum stop plate with a diameter of 400 mm

located 1.5 m behind the carbon foil. The emitted

secondary electrons on the stop plate are directed

to the stop MCP, to create the stop signal. A

magnetic lens is implemented to focus the electrons

on the stop MCP. This lens is placed outside of the

TOF detector and can be adjusted in position and

rotation for optimal detection efficiency. Radio-isotope is discriminated from remaining unwanted

particles by the flight time from start signal to stop

signal. The time resolution of this TOF system is 1

ns. The difference between the expected flight time

of 129I and 127I is 5 ns under the condition that the

momentum is same.

ionsSecondary electrons

Stop MCP

Start MCPStart foilMagnetic lens

Stop plate

Grid

Stop bend magnet

Start bend magnet

(Carbon foil)

Slit

Fig. 2. Principal layout of TOF detector. Bold lines denote incoming ions. Dotted lines denote secondary electrons which are emitted

from carbon foil and stop plate.

8.00

7.80

7.60

7.40

7.20

7.00

Target #1 Target #2 Target #3 Target #4 Average

129 I

/127

I (x

10-1

1 )

1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5

Run Number

Fig. 3. Measured 129I/127I ratios form the acceptance test on 17

July 2000. Samples (AgI) were prepared at IsoTrace Labora-

tory. In target #1–5 cells, error bars attached to all measured

points are calculated from counting statistics. In the average

cell, the large error bar (1r) was determined by all the mea-

surements and the small error bar (1r) gave the reproducibility(uncertainty) in the mean sample value.

T. Suzuki et al. / Nucl. Instr. and Meth. in Phys. Res. B 223–224 (2004) 87–91 89

3. Performance

3.1. Reproducibility and precision

The acceptance test for the iodine line was car-

ried out on two consecutive days (July 17 and 18,

2000). AgI (129I/127I ¼ 1.1 · 10�10) standard sample

was prepared by IsoTrace (University of Toronto).

After sputter cleaning for 5 to 10 min., four sam-ples were measured during several runs. One run

(about 10 min) was injected 60,000 times for 129I

and 127I. The resulting machine ratios on the first

day are shown in Fig. 3. A reproducibility was

calculated from the mean value per target and a

precision was calculated from 20 measurements (4

targets· 5 runs). On the first day, the resulting ratio

and standard deviation of the reproducibility andthe precision are (7.50± 0.12) · 10�11 (1.6%) and

(7.50 ± 0.15) · 10�11 (2.0%), respectively. On the

second day, they are (7.21± 0.05) · 10�11 (0.7%)

and (7.21 0.11) · 10�11 (1.5%), respectively [3]. This

demonstrates that this new 129I beamline has the

good reproducibility and precision. The difference

between standard and measured machine ratio

suggests that the transmission efficiency from the115� magnet to the TOF detector is about 70%,

which is probably dominated by the efficiency for

electron detection of MCP in TOF detector.

3.2. Detection limit

The detection limit of the new beamline for 129I/127I measurements was investigated with commer-cially available silver iodide (ACROS Co. Ltd.

lot# 13564/1), instead of the Woodward iodine

used elsewhere [6,7]. The measured ratio, uncor-

rected for any detector background or processingblank, is 2.3 · 10�13 which was normalized to the

IsoTrace standard and a TOF spectrum from these

measurements is shown in Fig. 4. This order is

consistent with 129I/127I values reported by other

AMS laboratories on samples that they processed

from commercially available potassium iodide

[6,8]. Since our measured TOF-detector spectrum

does not exhibit a background underneath the 129Ipeak, we conclude that the detection limit must be

100

80

60

40

20

0590 595 600 605 610 615 620

Channel

Cou

nts

5 ns

Fig. 4. TOF spectrum on commercial AgI material. One

channel corresponds to 1 ns. Measurement time to obtain this

spectrum is about 50 min.

Seawater Sample

I-+IO3-

Iodine Carrier (2mg)

CCl4NaNO2

Organic Phase(CCl4)

H2SO4NaHSO3

Inorganic Phase(Water)

NH3

AgNO3

Organic Phase(CCl4)

repeat (x5-6)

Inorganic Phase(Seawater)

I-

I2

AgI

I-

H2SO4+NaHSO3

Fig. 5. Flow chart of extraction method from seawater (see text

for details).

90 T. Suzuki et al. / Nucl. Instr. and Meth. in Phys. Res. B 223–224 (2004) 87–91

at least one order of magnitude lower than the

measured ratio. In the near future, this measure-

ment will be repeated using the Woodward iodine

instead, in order to compare with previously re-ported values in the range (4–9) · 10�14 [6,7].

3.3. Status

After the acceptance test, we encountered a

variety of problems with the new beamline. The

first was a crack in the stop MCP plate of the TOF

detector, and the second fault was an unexpectedclosing of the slit located in front of the carbon

foil. After repairing the slit from the outside and

replacing the start and stop MCP plates with new

ones, 129I was observed again. Despite this,

counting rates of the TOF detector have consid-

erably decreased some point in time after the

acceptance test. A probable cause is an earthquake

having affected the alignment of the high-energysection beamline behind the analysing magnet,

particularly that of the TOF detector. It is ex-

pected that realignment of that part of the beam-

line will solve this problem.

4. Sample preparation

Preparation of 129I-AMS targets from seawater

is performed by an extraction method [9], see the

flow chart given in Fig. 5. First, iodine carrier (2

mg) is added to the sample, about 1 L of seawater.

Iodate is reduced to iodide with sulfuric acid and

sodium hydrogen sulfite, and the iodide is oxidized

to I2 by the addition of sodium nitrite. The I2 isextracted with carbon tetrachloride and then back-

extracted into sodium bisulfite solution by reduc-

tion of I2. These extraction and back-extraction

steps are repeated until the color of carbon tetra-

chloride disappears with concentrating and puri-

fying the iodine. This usually requires repeating

this step 5–6 times. The concentrated iodine is

precipitated as silver iodide with silver nitrate andammonia in a dark room. The silver iodide is

rinsed by ammonia and distilled water. After

drying, the AgI is mixed with Nb (AgI:Nb¼ 1:2.5)

and pressed in a target holder.

T. Suzuki et al. / Nucl. Instr. and Meth. in Phys. Res. B 223–224 (2004) 87–91 91

5. Summary and outlook

The new beamline was optimized to measure129I/127I isotopic ratios, featuring sequential injec-

tion into the 3 MV Tandetron and particle detec-

tion by time-of-flight. Iodine isotopic ratios can be

measured with a precision better than 2%, and

inspection of the TOF detector spectrum suggests

that the detection limit is well below 10�13. The

high-energy section of this new beamline has had a

few problems since the acceptance tests, most ofwhich have been solved. It is expected that

realignment of that section will recover some or all

of the transmission that was lossed probably due

to an earthquake. A method has been described to

prepare 129I-AMS targets from seawater samples.

Two nuclear fuel reprocessing plants, at La

Hague (France) and Sellafield (England), have

released large quantities of 129I into seawater. Ithas been used as an oceanographic tracer in the

north Atlantic and Arctic oceans [9,10]. In Japan,

a new nuclear fuel reprocessing plant will be

operated at Rokkasho in the near future. We in-

tend to investigate the potential of using 129I as an

oceanographic tracer in the North Pacific Ocean,

using the emission of 129I from this Rokkasho

facility. Past dumping of radioactive waste in theJapan Sea by the Russian Federation and the

former Soviet Union [11] may complicate a

description of the 129I tracer source function in

that area. Sampling prior to the anticipated release

by the Rokkasho facility is expected to provide a

proper baseline. Hence, we consider the arrival ofthe Rokkasho plant as an opportunity and our

high-sensitivity 129I-AMS beamline as the right

tool to mount new marine environmental research.

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