a p p l i c at i o n N o t e
Liquid Scintillation Counting
Quantitation of Transuranium
Elements in High Activity
Waste (HAW) Using
Alpha/Beta Liquid
Scintillation Counting and
Extractive Scintillators
Abstract
Determining the content of transuranium elements, Americium
(Am), Plutonium (Pu), Neptunium (Np), and Curium (Cm) in the
nuclear fuel cycle and in nuclear radioactive waste is important
for both economic and human toxicity reasons. The major
concern is processing the sample rapidly and quantitating these
transuranium alpha emitters in the presence of 105 fold excess
of beta emitting contaminants. The combination of alpha/beta
discrimination with a PerkinElmer Tri-Carb® Liquid Scintillation
Analyzer employing the Pulse Decay Analysis (PDA) technique
and extractive scintillators allows the quantitation of a small
concentration of alpha radionuclides in the presence of a large
excess of beta emitters without an excessive amount of sample
preparation. Both the pulse decay analysis method and extractive
scintillator performance are discussed.
Introduction
The quantitation of transuranium elements is important in
radioactive waste management. The content of transuranium
elements in high level radioactive waste (HAW) has a direct
influence on the selection of the proper disposal method.
HAW is characterized by its high beta and gamma radioactivity,
complex chemical constituents (high salt concentration),
and low concentration of transuranium elements. The total
activity of this waste is approximately 3.7 X 1013 Bq/L with a
concentration of 250 g/L. The concentration of the transuranium
elements is only 0.07-0.35 g/L or a 3000 fold excess of beta to
alpha particles.
Author
Jim Floeckher
Traditionally, alpha particles have been quantitated with
ZnS(Ag) scintillation detectors and proportional counters. Alpha
spectroscopy has been performed by surface-barrier detectors
and grid ionization chambers. All of these methods measure solid
samples on planchets. Sample preparation is a difficult problem
because of the self-absorption of the alpha particle by the sample
matrix or by the alpha particle itself.
Several complicated and long procedures, including precipitation,
filtration, chromatography, extraction, and stripping are required
to separate the alpha emitting nuclides of interest from the
sample matrix (HAW).1 In addition, evaporation, electrodeposition,
and vacuum sublimation are necessary to prepare the samples
for accurate analysis by one of these methods.1 These combined
procedures are labor intensive and time consuming. They result in
low counting efficiencies, low recoveries, and poor reproducibility.
To reduce the amount of time and effort required to process
and quantitate the alpha component in HAW, liquid scintillation
counting employing Pulse Decay Analysis (PDA) and the use of
extractive scintillators was investigated
Experimental
The major radioactive components of HAW are shown in
Table 1. All activities are relative to the activity of Neptunium.
The total relative beta activity is 1.05 X 106, and the transuranium
activity level is from 1 to 400. To evaluate both the pulse decay
analysis and extractive scintillator techniques, both synthetic and
typical high activity waste (HAW) samples were examined and the
radioactivity of the major components determined.
237
*Relative
Activity
= activity
of the
of 237Np.
*Relative
Activity
=
of
the
of
*Relative
Activity
= activity
activity
ofnuclide/activity
the nuclide/activity
nuclide/activity
of 237Np.
Np.
Table 1.
Table Elements
1.
Table 1. Relative Radioactivities of Transuranium
and Some F.P.S. in HAW.
Relative
Relative Radioactivities
Radioactivities of
of Transuranium
Transuranium Elements
Elements and
and Some
Some F.P.S.
F.P.S. in
in HAW.
HAW.
Figure
1.
Figure
1.
241
Figure 1. Spectra of 106Ru/106Rh and 241Am in a Mixed Sample
Spectra of
of 106
Ru/
106Rh and 241Am in a Mixed Sample
10 ml 5 g/l PPO-0.5 g/l M2POPOP-50
g/lRu/
Naphthalene-Toluene-Triton.
Spectra
Rh and Am in a Mixed Sample
10
10 ml
ml 5
5 g/l
g/l PPO-0.5
PPO-0.5 g/l
g/l M
M22POPOP-50
POPOP-50 g/l
g/l Naphthalene-Toluene-Triton.
Naphthalene-Toluene-Triton.
106
106
Page
Page 22 –– Application
Application Note
Note
2
Figure 2. Extraction Separation Procedure of Np, Pu, and Am from HAW
Figure 2.
Extraction Separation Procedure of Np, Pu, and Am from HAW
Application Note – Page 3
3
To quantitate the alpha emitters by liquid scintillation counting,
a PerkinElmer Tri-Carb Alpha/Beta Liquid Scintillation Analyzer
with special
Pulse Decay
(PDD)
is used.
To quantitate
theDiscrimination
alpha emitters
by circuitry
liquid scintillation
This circuit
discriminates
alpha
particles
from
beta
particles
counting, a Packard Tri-Carb Alpha/Beta Liquid Scintilbased on
theirAnalyzer
pulse decay
time
and is Pulse
the basis
of the
Pulse
lation
with
special
Decay
Discrimination (PDD)
circuitry
is used.
circuit
discriminates
Decay Analysis
(PDA)
technique.
AlphaThis
particles
produce
alpha
particles
fromwhich
beta particles
based
on their pulse
pulses in
a liquid
scintillator
take several
hundred
decay
time
and
is
the
basis
of
the
Pulse
Decay
Analysis
nanoseconds to decay compared to beta pulses which take
a
(PDA) technique. Alpha particles produce pulses in a
few nanoseconds to decay. Once the PDD circuit is optimized
liquid scintillator which take several hundred nanosecfor theonds
cocktail,
pulsescompared
which have
timeslonger
to decay
to decay
beta pulses
whichthan
takethe
a few
PDD setting
are
classified
as
alpha
and
placed
in
an
alpha
MCA
nanoseconds to decay. Once the PDD circuit is
optiand those
thatfor
have
decay
timeswhich
are classified
as beta
mized
theshorter
cocktail,
pulses
have decay
times
longer
PDD setting are classified as alpha and
and placed
in athan
betathe
MCA.
placed in an alpha MCA and those that have shorter de-
cay times
are classified
as beta
and placed in a beta
Alpha/Beta
Discrimination
Without
Extractive
MCA.
Scintillators
Alpha/Beta
Discrimination
Without
Extractive
A mixed
synthetic alpha/beta
sample of
HAW that
contained a
Scintillators
150 fold
excess of 106Ru (beta emitter), and its daughter, 106Rh
A beta/gamma
mixed synthetic
alpha/beta
sample offound
HAWinthat
con(a mixed
emitter),
both 106
commonly
spent
tained a 150 fold excess
of
Ru
(beta
emitter),
and
its
nuclear fuel, was mixed
with 241Am. The sample was counted
daughter, 106Rh (a mixed beta/gamma emitter), both
directlycommonly
in the liquidfound
scintillation
counter
with
pulse
in spent
nuclear
fuel,
wasdecay
mixed with
241
discrimination,
without
the use
extractants.
The spectra
Am. The
sample
wasofcounted
directly
in the in
liquid
Figure 1A
show the relative
the alpha
and beta
scintillation
countercontributions
with pulse to
decay
discrimination,
theis use
of extractants.
Thetospectra
in Figure
MCAs.without
The y-axis
re-scaled
in Figure 1B
better show
the 1A
showinthe
contributions
to beta
the alpha
beta
alpha peak
the relative
alpha MCA
relative to the
activityand
in the
MCAs.
The1Cy-axis
is re-scaled
1B to Itbetter
beta MCA.
Figure
is the alpha
peak inin
theFigure
alpha MCA.
is
show the alpha peak in the alpha MCA relative to the
obvious that with PDD, the contribution of beta activity to the
beta activity in the beta MCA. Figure 1C is the alpha
alpha MCA
small MCA.
even inItspite
of a large
peak isinquite
the alpha
is obvious
thatbeta
withexcess
PDD, the
in the sample.
In fact,
PDA
method
effective
for direct
contribution
ofthe
beta
activity
to isthe
alpha MCA
is quite
measurement
of samples
ratio of
250/1
betaintothe
alpha.
small even
in spitewith
of aa large
beta
excess
sample.
As can be seen in Table 1, it is common for samples of HAW
to have a beta/alpha ratio of up to 105/1. To quantitate the
alphas
in these
samples,
a combination
of PDAfor
andsamples
extractive
As can
be seen
in Table
1, it is common
of
scintillators
used. Extractive
HAW tomust
havebe
a beta/alpha
ratio scintillators
of up to 105selectively
/1. To quantitate
the alphas
in these from
samples,
a combination
PDA
isolate
certain
radionuclides
samples
prepared atof
various
extractive scintillators
must
be used.
Extractive
acidand
concentrations.
A scheme using
extractive
scintillators
to
scintillators
isolate
certain
radionuclides
isolate
Neptuniumselectively
(Np), Plutonium
(Pu),
and Americium
(Am) is
from samples prepared at various acid concentrations. A
shown in Figure 2.1
scheme using extractive scintillators to isolate Neptunium (Np), Plutonium (Pu), and Americium (Am) is
Alpha/Beta Discrimination
With Extractive Scintillators
shown in Figure 2.1
To investigate the use of both alpha/beta LSC and extractive
Alpha/Beta Discrimination With Extractive
scintillators, the activity of Pu in a HAW sample was
Scintillators
determined.
The total
the sampleLSC
is 8 Xand
104exTo investigate
thebeta
use activity
of bothofalpha/beta
higher
thanscintillators,
the alpha activity.
If the sample
directly
tractive
the activity
of Pu inis aanalyzed
HAW sample
with
PDA,
without any
extractive
processes,
spectral
datais
was
determined.
The
total beta
activity the
of the
sample
higher
alpha aactivity.
If the of
sample
8 Xthat
104the
shows
betathan
MCAthe
contains
large number
countsis
analyzed
directly
with
PDA,
without
any alpha
extractive
across
the entire
energy
range
(Figure
3). The
MCA processes,
the
spectral
data
shows
that
the
beta
MCA
shows only 0.3% of the total counts in this MCA, but no conpeak
tains a large number of counts across the entire energy
is apparent for the Plutonium. If the HAW sample is extracted
range (Figure 3). The alpha MCA shows only 0.3% of
with
di-(2-ethylhexyl)-phosphate
in toluene
cocktail
the
total counts in this MCA,(HDEHP)
but no peak
is apparent
for
the Plutonium. If the HAW sample is extracted with di-
(see(2-ethylhexyl)-phosphate
Figure 2) and the organic phase
is counted
with Pulse
(HDEHP)
in toluene
cocktail
Decay
Analysis,
the
alpha
component
is
easily
isolated.
(see Figure 2) and the organic phase is counted with
Figure
4 shows
spectra the
of both
alpha andisthe
betaisoPulse
Decaythe
Analysis,
alphathe
component
easily
lated. Figure
4 shows
the spectra
of the
both180,000
the alpha
and
components
in their
respective
MCAs. Of
CPM
the beta
components
insample
their respective
the
initially
present
in the HAW
only 2,600MCAs.
CPM areOf
found
180,000
CPMThus,
initially
presenteliminates
in the HAW
sample
in the
extractant.
extraction
greater
thanonly
2,600 CPM are found in the extractant. Thus, extraction
98% of the beta activity and the remaining 2% of beta can
eliminates greater than 98% of the beta activity and the
be discriminated from the alpha activity by PDA. The 239Pu can
remaining 2% of beta can be discriminated from the aleasily
recognized
as a peak
in Pu
thecan
alpha
MCA
4) and
phabeactivity
by PDA.
The 239
easily
be(Figure
recognized
quantitated
using
this
combined
technique.
as
a
peak
in
the
alpha
MCA
(Figure
4)
and
quantitated
In fact, the PDA method is effective for direct measure-
ment of samples with a ratio of 250/1 beta to alpha.
using this combined technique.
Figure 3. Spectra of HAW without Separation; 10 ml 5 g/l PPO-0.5 g/l M2POPOP-50 g/l
Figure 3.
Naphthalene-Toluene-Triton.
Spectra of HAW without Separation; 10 ml 5 g/l PPO-0.5 g/l M2POPOP-50 g/l
Naphthalene-Toluene-Triton.
Page 4 – Application Note
4
Figure 4. Spectra of 239Pu in HDEHP - Organic Solution After Extraction from HAW;
10 ml 5 g/l PPO-0.5 g/l M2POPOP-50 g/l
Naphthalene-Toluene-Triton.
Figure
4.
Spectra of 239Pu in HDEHP - Organic Solution After Extraction from HAW;
10 ml 5 g/l PPO-0.5 g/l M2POPOP-50 g/l Naphthalene-Toluene-Triton.
Application Note – Page 5
5
Figure 5. Extraction Separation Procedure of Np from HAW.
Figure 5.
Extraction Separation Procedure of Np from HAW.
Page 6 – Application Note
6
Figure 6. Spectra of 237Np in TiOA - Organic Solution After Extraction from HAW;
10 ml 5 g/l PPO-0.5 g/l M2POPOP-50 g/l Naphthalene-Toluene-Triton.
Figure 6.
Spectra of 237Np in TiOA - Organic Solution After Extraction from HAW;
10 ml 5 g/l PPO-0.5 g/l M2POPOP-50 g/l Naphthalene-Toluene-Triton.
Conclusion
Conclusion
Reference
Reference
The
quantitation
of of
high
levellevel
radioactivity
wastewaste
from the
The
quantitation
high
radioactivity
from
nuclear
fuel
cycle
or
radioactive
waste
management
is difficult,
the nuclear fuel cycle or radioactive waste management
is difficult,
and time
consuming
becausetoit is
laborious,
andlaborious,
time consuming
because
it is necessary
necessary
to
eliminate
the
interference
of
the
large
eliminate the interference of the large excess of beta
andexcess
of
beta
and
gamma
radionuclides
before
measuring
gamma radionuclides before measuring the alpha activity.
the alpha activity. To quantitate the alpha particles, sevTo quantitate the alpha particles, several separations and
eral separations and sample preparation steps are resample
steps are
required
prior to analysisBy
with
quiredpreparation
prior to analysis
with
alpha spectrometry.
usalpha
spectrometry.
By
using
the
liquid
scintillation
pulse
decay
ing the liquid scintillation pulse decay analysis method,
analysis
method,
alphas
can
be
accurately
quantitated
despite
alphas can be accurately quantitated despite a 250 fold
betas of
without
any extraction
methods.
Ratios
a excess
250 foldofexcess
betas without
any extraction
methods.
in
excess
of
250/1
beta/alpha
can
be
quantitated
by
Ratios in excess of 250/1 beta/alpha can be quantitatedcomby
bining the
extractivescintillators.
scintillators.
combining
thePDA
PDA technique
technique with
with extractive
Together, these two techniques can be used effectively
Together, these two techniques can be used effectively to
to quantitate alphas in the nuclear fuel cycle and nuclear
quantitate alphas in the nuclear fuel cycle and nuclear waste
waste samples in a simple, rapid, and accurate manner.
samples in a simple, rapid, and accurate manner.
Yang,Dazhu,
Dazhu,“ “
Study
Determination
of Np,
1. 1.Yang,
Study
onon
Determination
of Np,
Pu,Pu,
andand Counting and
Am
Amwith
withExtraction-Liquid
Extraction-Liquid Scintillation
Scintillation Counting
and Its Its
Application
to
Assay
of
Transuranium
Elements
Application to Assay of Transuranium Elements in in
High-
High-Level Radioactive Waste, Ph.D. thesis, Tsinghua
University,
Level Radioactive
Ph.D.1990.
thesis, Tsinghua University, Beijing, Waste,
P.R. China,
Beijing, P.R. China, 1990.
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April 2011
Application Note – Page 7