Nuclear Science and Engineering Research

8-7

Analysis of Age Determination of Individual Plutonium Particles－ Contribution of Development of Ultra-Trace Analytical Technique to IAEA Safeguard Activity －Purification of Pu reference solution
10 μm

Development oftechnique for preparing Pu particles

Dissolution of single Pu particle

Addition of 243Am solution
Development of techniquefor ion-exchange separation of Pu and Am
Development of isotope ratio measurement243
Am/239Pu, 241Pu/239Pu, 241Am/243Am

Determination of Pu purification age
deduced from 241Am/241Pu ratio

1 μm

Fig.8-19 Pu particles prepared from a Pu reference solution
Micron-size age-known Pu oxide particles (right) were prepared.
A technique for isolating a single particle was developed. Theage of an isolated Pu particle (left) was determined.
Difference from the actual age (year)

Development oftechnique for isolating single Pu particles

The microneedle
attached to a SEM forthe isolation of a single
Pu particle.

0.8

Actual Pu purification age: 3.92 years

0.6
0.4
0.2

average
0.11 years(41 d)

0.0–0.2–0.4
12345 6 7Sample No.

8

Fig.8-18 Development of analytical procedure for Pu
purification age determination
An analytical technique for determining the purification age ofan ultrafine Pu particle was realized by combining techniques
for preparing a single Pu particle and for chemical separation.

Fig.8-20 Pu purification age of single Pu particles determinedby 243Am spike method
The average age of eight Pu particles was in good agreement withthe actual age (3.92 years) with a difference of 0.11 years (41 d).

Inspectors from the International Atomic Energy Agency(IAEA) take an environmental sample such as dust by wiping
the floors in a nuclear facility, and the amount and isotopic
composition of ultra-trace (10-15–10-12 g) uranium (U) andplutonium (Pu) are analyzed to detect undeclared nuclearactivities.
We developed a technique for isolating a single Pu particle
and an analytical technique for the precise determination of
the Pu purification age to upgrade the methods used to manage
nuclear materials in Japan (Fig.8-18). The Pu purification age
is evaluated by measuring the americium-241 (241Am)/241Pu
atomic ratio precisely. A single Pu particle of ultra-trace amount(<10-12 g) should be analyzed because Pu of different origins
may be mixed in a sample. 241Am and 241Pu must be chemicallyseparated before they are subjected to mass spectrometry
because they have the same atomic mass and cannot be
separated with a mass spectrometer. The known techniques
cannot provide the precise age of young Pu samples or ultratrace samples because of the low 241Am/241Pu atomic ratio. It isalso necessary to prepare a reference sample of young single
Pu particles for evaluating the accuracy and precision of ouranalytical results. We developed the following techniques: thepreparation of micron-diameter Pu oxide particles (Fig.8-19)
from Pu purified by ourselves; a technique for isolating a single
Pu particle by a microneedle attached to a scanning electron
microscope (SEM); and chemical separation and isotope
measurement of ultra-trace Pu and Am.
Precise measurement of the 241Am/241Pu ratio in a single Pu
particle of 10-12 g was achieved. Each Pu particle was dissolved
and spiked with pure 243Am. The 241Am/241Pu ratio was obtained
from the 243Am/239Pu ratio of a sample solution and the isotope
ratios of Pu and Am in the chemically separated fractions.
These ratios were measured with an inductively coupled plasma
mass spectrometer. The determined age was in good agreementwith the actual age (3.92 years), with a difference of 0.11 years(41 d) on average (Fig.8-20). By using this analytical technique,traces of nuclear activity can be detected. We can contributeto the IAEA safeguard activity by analyzing samples with ourexcellent techniques.
The present study was sponsored by the Ministry ofEducation, Culture, Sports, Science and Technology of Japan(MEXT).

Reference
Miyamoto, Y. et al., Precise Age Determination of a Single Plutonium Particle using Inductively Coupled Plasma Mass Spectrometer, Radiochimica Acta,
vol.101, issue 11, 2013, p.745-748.

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JAEA R&D Review 2013