b_2009_043_12
TRANSCRIPT
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Abstract
Unknown nuclear material may originate rom sev-
eral sources. Nuclear orensics allows by using fn-
gerprinting and comparison with reerence data to
determine the origin, the intended use, the last legal
owner and the smuggling route. These inormation
are essential in the cause o thet or diversion as
measures o saeguards can be implemented to
prevent future thefts.
Certain measurable parameters can point to a spe-
cifc material and provide thereore a fngerprint o
the unknown material. Comparing the measured pa-
rameters with reerence material give clues to the
origin and the last legal owner.
Characteristic parameters and possible inormation
they contain are presented.
Keywords: nuclear orensics; uranium; plutonium.
1. Introduction: What is nuclear orensics?
As the ormer Soviet Union disintegrated in the ear-
ly 1990s a new phenomenon was discovered nu-
clear smuggling. The frst cases were reported in
1991 in Switzerland and in Italy. New questions had
to be answered: intended use o the unknown nu-
clear material, its origin, the last legal owner and the
smuggling route. Techniques to answer these ques-
tions were known rom nuclear saeguards and ma-
terial science. Combining these analytic methods
was the starting point o nuclear orensics.
Inormation that is obtained by nuclear orensic
analysis can be divided into two groups: endogenic
and exogenic inormation.
Endogenic inormation is meant as sel-explaining
inormation as age, intended use and mode o pro-
duction, or which only model-calculation might be
required or data interpretation.
Exogenic inormation is meant as inormation bycomparison. To interpretate exogenic inormation
which include geolocation and production data
comparison with reerence data and reerence in-
ormation is necessary. Great eorts are made to
set up databases containing such reerence data.
Case development in nuclear orensics ollows a
deductive way (Fig. 1). Taking the available results
into account a hypothesis or a set o hypotheses
are built. Databases and other experts serve or the
knowledge to build the hypothesis. Further analysis
has to be made to prove the presence o signaturesaccording to the hypothesis. I the signatures are
absent in the sample a new hypothesis has to be
developed.
Figure 1: The deductive way in the nuclear orensic
process [1].
2. The nuclear fngerprint method
To characterize an unknown nuclear material a set
o items are measured to establish the so called nu-
clear fngerprint. Inormation that orm the nuclear
fngerprint are:
Macroscopicparameters (e.g.pellet diameter,
height)
Isotopiccomposition
Fingerprinting of Nuclear Material for Nuclear
Forensics
A. Redermeier
Vienna University of Technology, ATOMINSTITUT, Bahnhofstrae 46, 2231 Strasshof, Austria
E-mail: [email protected]
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Elemental composition (suchaselementsand
impurities)
In cases o a mixture o components, a powder or i
it may be possible that substances o dierent
chemicals or isotopic composition have been add-
ed, it is necessary to investigate the microstructu-
rual fngerprint which consists o ollowing items:
Particlemorphology
Particlesizeandsizedistribution
Grainsizeandsizedistribution
Porositysizedistributionanddensity
Dislocationdensityandcharacter
Precipitationofotherphases.
2.1. Isotopic patterns o U and Pu
The ollowing inormation can be obtained by inves-
tigating the isotopic patterns:
ThepresenceofsmallamountsofU-236willin-
dicate a contamination with recycled uranium
and hence point at reprocessing activities.
Theisotopiccompositionofplutoniumisauseful
indicator o the reactor type in which the material
was produced.
Uraniumoxidecanbefoundindifferentforms,e.g. UO2 or U3O8, which give inormation on vari-
ous points o origin in the uranium uel cycle.
Plutonium is generated as by-product in nuclear re-
actors when 238U absorbs a neutron creating 239U,
which -decays into 239Np and fnally to 239Pu. Also
heavier isotopes o Plutonium are produced by ur-
ther neutron captures. Thereore the isotopic com-
position may give answers which reactor type was
used to produce the unknown nuclear material.
The isotopic composition o Plutonium provides in-ormation to indicate the type o the reactor:
Thehighertheinitial235U enrichment o the uel
is, the higher is the 238Pu abundance due to mul-
tiple neutron capture on 237Np.
TheneutronenergyspectruminuencesthePu
isotopic composition (the soter the spectrum,
the higher is the 242Pu/240Pu ratio).
The measured isotopic patterns can be compared
with model calculations using computer codes (e.g.ORIGEN or SCALE or the RBMK and the VVER). It
was demonstrated that the main reactor types can
be separated clearly rom each other (Fig. 2).
Figure 2: Calculated isotopic composition o Pluto-
nium or various reactor types (continuous line) and
measured isotopic composition (points) [2].
2.2. Age determination
The age is defned as the time elapsed since the
last chemical processing took place (e.g. produc-
tion, reprocessing or purifcation). The age o the
material may serve as exclusion parameter in the
search or the production or reprocessing plant.
Since radioactive isotopes decay at a rate deter-
mined by the initial amount and the hal-lie o the
isotope, the relative amounts o decay products
(daughters) in comparison to the parent isotope can
be used as chronometer.
The age o the material is short in comparison to
the hal-lie o the observed nuclides. Using the ta-
ble o nuclides many parent/daughter pairs can be
ound. The optimal nuclide ratios or Uranium are:
234U/230Th
235U/231Pa
and or Plutonium:
238Pu/234U
239Pu/235U
240Pu/236U
241Pu/241Am.
The radioactive decay o each o these nuclides is
unique, thereore measuring the parent/daughter
ratio allows to calculate the time elapsed since the
last chemical separation. I the material has not
been ully separated, the chronometer hasnt been
set properly to zero and so misleading inormationabout the age is gained. To avoid this systematic
error it is recommended to measure various parent/
daughter ratios.
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Figure 3: The parent/daughter mass ratios o aged
plutonium material [3].
2.3. Metallic impurities
Nuclear material contains metallic impuritites at var-
ying concentrations. In the starting materials metal-
lic impurities are accompanying elements, during
processing to the intermediate and fnal product the
impurities are drastically reduced. A reduction ac-
tor o 103 in the impuritity level is possible ater
processing. Impurity patterns within the processing
remain or the most mines the same.
Otherwise metallic impurities may enter in the nu-
clear material at the dierent processing stages. The
systematic behind this is not well understood up tonow, but a ull theory must contain that the concen-
tration o the impurities are a unction o exposure
time to the container material or storage tank as
they are leached rom the surace o the walls.
Nowadays in sample analysis the ratio o elements
o similar chemical behaviour are examined be-
cause the ratio will vary only within narrow limits.
2.4. Stable Isotopes
Measuring the stable isotopes is a established tech-nique in geolocation. Two substances which are
chemically identical have dierent stable isotope
compositions i either their origin and/or their history
are not the same. In nuclear orensics the oxygen and
the lead isotope ratio measurements are applied.
2.4.1. Oxygen
Natural oxygen exists in three stable isotopes: 16O
(99.762%), 17O (0.038%) and 18O (0.200%). Tem-
perature, latitude and distance to the sea cause
variations up to 5% in the 18O/16O ratio.
Water is used as a common solvent in uranium
processing. During the processing isotopic ex-
change takes place and the fnal U-oxide product
carries the signature o the 18O/16O ratio o the used
water. Measuring the oxygen isotope ratio provides
inormation about the geographical region where
the material was processed. Figure 4 shows the
correlation between the geographic location o the
production site o uranium oxid examples and thevariation in the (18O)/(16O) ratio.
Figure 4: Comparison o the 18O/16O ratio o U3O8
or dierent uranium mines. Olympic and Ranger
are Australian mines [4].
2.4.2. Lead
From the our stable lead isotopes one is primordial
(natural) 204Pb and the other three are endproducts
o radioactive decay series: 238U 206Pb, 235U 207Pb, 232Th 208Pb. Thereore the stable lead iso-
tope composition gives inormation on the initial
U/Th ratio in the mine and on the age o the ore.
Due to the act that the variations in the composi-
tion or dierent mines are signifcant, investigating
the stable lead isotopes can locate the origin mine.
2.5. Anionic impurities
Uranium crude ore undergoes dierent chemical
processes beore it becomes uranium ore concen-
trate (yellow cake). Since uranium is mined rom
ores with dierent mineralogical natures (acidic, al-
kaline and phosphatic ores) dierent chemical leach-
ing processes are used. In the subsequent process-
ing also dierent chemical processes are used or
the precipitating and dissolving the uranium.
Dierent acids are used or the dierent processesand may leave anionic impurities (Cl-, F-, Br-, NO2-,
NO3-, SO4
2- and PO43-). These anions may be an in-
dicator or the process used.
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In practice anion ratios are used because the leach-
ing rate in the mines can change and absolute anion
concentrations dier more than the ratios.
It has been shown that anionic impurities can distin-
guish between dierent mines (Fig. 5), but there are
also dierences between dierent sampling cam-
paigns in the same mine (Ranger-old vs. Ranger-resh and Beverly-old vs. Beverly-resh in Fig. 5).
Figure 5: Anion ratios in dierent uranium ore con-
centrate samples [5].
2.6. Limitations o these techniques
2.6.1. Cross contamination
There are two problems which may cause crosscontamination by investigating the stable lead iso-
topes. First, natural lead (204Pb) is omnipresent so
special care has to be taken perorming the chemi-
cal separation second, lead is oten used as
shielding material.
Presently the methods o the analysis are continu-
ously improved. I the methods are sensitive enough
to detect even metallic impurities rom the spatula
used to collect the evidence, new problems or the
analysts are created.
2.6.2. Reprocessing and enrichment
Presence o 236U can point to reprocessing activi-
ties. It has also been shown that in natural uranium
variations in 236U and in 234U abundances occur.
Better measurement methods have to be developed
or 236U abundance levels close to natural abun-
dance.
I nuclear material was reprocessed or non-peace-
ul purposes the identifcation o this material is verychallenging. Additional inormation is necessary to
calculate predictive signatures or enriched uranium
produced rom reprocessed uranium [8]:
The 232U content does not only depend on the
operation mode o the production reactor but
also on non-reactor-related history (i.e. length o
storage periods beore and ater irradiation).
HEUmaybeenrichedinasinglecascade,butit
is also possible to use several interconnected
smaller cascades.
The identication of the enrichment process
(gaseous diusion vs. gas centriuge) due to
small dierences in the concentrations o the
trace uranium isotopes (232U, 234U and 236U) is
very challenging.
2.6.3. Blending
A special challenge to determine origin o nuclear
material arises i it is blended. In ormer times Rus-
sia blended the spent VVER uel with spent uel opropulsion reactors, ater reprocessing this nuclear
material is suitable or RBMK reactors [9].
Thereore the nuclear material measured value o
the 238Pu/tot.Pu vs. 242Pu/240Pu value will not ft the
simulated values (Specimen R1 in Fig.2).
Sometimes however cross-contamination has oc-
curred beore collection to disguise the origin.
Transmission electron microscopy (TEM) is used to
determine the grain-size distribution and can there-
ore indicate that a powder consists o dierent par-
ticle types.
2.6.4. Computer codes
Estimating the uncertainty o all quantities used in
the calculations (i.e. cross sections) and determin-
ing how these uncertainties propagate through the
entire simulation is called uncertainty analysis.
Uncertainty analysis is not implemented in the ORI-
GEN2 and SCALE code.
An interesting overview how to determine the un-
certainty in such computer codes is given in [10].
3. Overview o analytical techniques used in
nuclear orensics
Due to the tremendous fngerprint diversity and the
requirement o high accuracies o measurement
many dierent analytic techniques have to be ap-
plied in nuclear orensics. Figure 6 gives a short
overview o inormation gained rom Uranium andPlutonium samples and which analytic techniques
are required to obtain this inormation. A short over-
view o most widely used techniques is given in [2].
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3.1. Including traditional orensic methods
Wherever he steps, whatever he touches, whatever
he leaves, even unconsciously, will serve as a silent
witness against him. Not only his fngerprints or his
ootprints, but his hair, the fbers rom his clothes,
the glass he breaks, the tool mark he leaves, the
paint he scratches, the blood or semen he deposits
or collects. All o these and more, bear mute wit-
ness against him. This is evidence that does not for-
get. It is not confused by the excitement of the mo-
ment. It is not absent because human witnesses
are. It is factual evidence. Physical evidence cannot
be wrong, it cannot perjure itself, it cannot be whol-
ly absent. Only human ailure to fnd it, study and
understand it, can diminish its value.
Dr. Edmond Locard
This is the amous Locards Exchange Principle that
states that every contact leaves a trace. Traditional
orensic methods establish relations between loca-
tions, events and individuals - entirely other inorma-
tion than the nuclear orensic methods. In summary
orensic methods provide inormation adherent to
the material while nuclear orensic methods provide
inormation inherent to special nuclear material [7].
A detailed description o collecting both nuclear
and traditional orensic evidence is given in the Nu-
clear Forensics Support [1]. During the collection o
evidence and analysing the evidence in a laboratory
special attention has to be taken on sufcient pro-
tection against the radiation.
To ulfl good radiological saety practice the Insti-
tute or Transuranium Elements developed jointly
with the German Federal Criminal Police a so called
glove-box, where contaminated evidence can be
visually inspected, photographed and fngerprints
and DNA samples can be taken (Fig. 7).
Figure 7: Glove-box or handling o special nuclear
material [7].
4. Data interpretation
Measured exogenic inormation (such as 18O/16O ra-
tio, Pb isotopic composition, impurities and micro-
structure) needs comparison with reerence data
rom known samples.
4.1. Supporting inormation
It is important to have access to reerence data and
to keep inormation, that may vary with time (e.g. as
seen in 2.5. level o impurities), up to date. The re-erence inormation can be gained rom Nuclear Ma-
terials Database, Open Literature, ITDB, IAEA Re-
search Reactor Database, other databases and
comparison samples.
The Nuclear Materials Database was established in
collaboration between the ITU in Karlsruhe with the
A. A. Bochvar Institute in Moscow. The database
contains inormation on uels or commercial reac-
tors as collected rom open literature and rom bi-
lateral agreements with uel suppliers.
Figure 6: Inormation that can be obtained rom nuclear (U, Pu) material and used analytic techniques [6].
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Certain data have limited accessibility (commercial-
ly sensitive data such as chemical impurities) or are
not shared (detailed inormation on weapons grade
material).
4.2. Exclusion Principle
In order to avoid a ull characterization each timewhen unknown nuclear material is ound, the exclu-
sion principle is applied. The exclusion principle
works as ollows:
1. The frst measured inormation (e.g. pellet dimen-
sions and isotopic composition) are compared
with the database entries.
2. The non-matching records are rejected as they
could not be manuacturer o the unknown nu-
clear material.
Exit condition: A single record is let. This is thebest case.
3. The remaining records, which match the meas-
urements, are compared to each other in order
to identiy parameters which could distinguish
between these records.
Exit condition: No urther parameters can be in-
vestigated.
4. These parameters are measured next.
5. The measured data are compared with the re-
duced database entries.Go back to 2).
5. Conclusion
Combining various analytic techniques can give in-
ormation about the origin, the intended use, the last
legal owner and the smuggling-route o unknown
nuclear material. But this is only possible i enough
reerence datas are available and accessible.
Thereore it is necessary to strengthen the interna-
tional cooperation and the cooperation with the uel
manuactors.
Since the beginning o nuclear orensics in the early
1990s more and more parameters proved to be use-
ul and could be applied or the nuclear fngerprint.
Hence it is necessary to do urthermore research
and development and to keep close cooperation
with other sciences whether new characteristic pa-
rameters can be investigated.
6. Acknowledgement
The author would like to thank the European Sae-
guards Research and Development Association,
Working Group on Training & Knowledge Manage-
ment or organising the 5th ESARDA course.
Reerences
[1] IAEA; Nuclear Security Series No 2, Nuclear Forensics Sup-
port, Vienna, Austria, 2006, http://www-pub.iaea.org/MTCD/
publications/PDF/Pub1241_web.pd[2] Mayer K. et al; Nuclear orensicsa methodology providing
clues on the origin o illicitly trafcked nuclear materials, Ana-
lyst, 2005, 130, 433441
[3] Wallenius M., Mayer K: Age determination o plutonium mate-
rial in nuclear orensics by thermal ionisation mass spectrom-
etry, Fresenius J Anal Chem (2000) 366 :234238
[4] Advances in destructive and non-destructive analysis for envi-
ronmental monitoring an nuclear orensics, Karlsruhe, Germa-
ny, 2002, http://www-pub.iaea.org/MTCD/publications/PDF/
pub1169_web.pd
[5] Badaut V. et al;Anion analysis in uranium ore concentrates by
ion chromatography, Journal o Radioanalytical and Nuclear
Chemistry, Vol. 280, No.1 (2009) 5761
[6] Wallenius M. et al; Nuclear orensic investigations: Two case
studies, Forensic Science International 156 (2000) 55-62
[7] Mayer K. et al; Nuclear orensic science From cradle to ma-
turity, Journal o Alloys and Compunds 444-445 (2007) 50-56
[8] Joint Working Group o the American Physical Society and the
American Association or the Advancement o Science; Nu-
clear Forensics Role, State of the Art, Program Needs
[9] Wallenius M. et al; Origin determination o Plutonium material
in nuclear orensics, Journal o Radioanalytical and Nuclear
Chemistry, Vol. 246, No. 2 (2000) 317-321
[10] NUREG/CR-5625, ORNL-6698; Technical support or a pro-posed decay heat guide using SASH2/ORIGEN-S data