Application Note: A Rapid Procedure for Screening Transuranium Nuclides in Urine Using Actinide Resin and Low Level

a p p l i c at i o n N o t e

Liquid Scintillation Counting
A Rapid Procedure for
Screening Transuranium Authors
Nuclides in Urine Using J. Eikenberg, I. Zumsteg, M. Rüthi

Actinide Resin and Low S. Bajo, Paul Scherrer
Institute CH-5232 Villigen (PSI) Switzerland

Level a/b-LSC C. J. Passo
PerkinElmer, Inc.
Waltham, MA, USA

M. J. Fern
Eichrom Industries, Inc.
Darien Illinois, USA

Abstract Introduction
A fast and simple radiochemical procedure for determining One of the most extensive tasks in the field of bioassay analysis
a-emitting nuclides in urine is presented. The method is is the determination of pure a- (and b-) emitting radionuclides
based on a/b-LSC using the Tri-Carb® with alpha/beta from the nuclear fuel cycle such as 234U and 235U, or anthro-
discrimination as well as on the high selectivity of Eichrom’s pogenic 239Pu and 241Am in urine samples. However, any
actinide resin for heavy isotopes with atomic numbers above radiochemical method, which is applied to perform such
90 (i.e., Th, U, transuranium nuclides). Under optimized analyses, has to be highly sensitive since even small amounts
pulse shape discriminator settings, a very efficient a/b of incorporated radionuclides decaying by a emission may
discrimination of only 0.1% spill-over of b into a was contribute to harmful doses to human organs.1
obtained at 95% counting efficiency for a-pulses. In
addition, using a mixture of the scintillation liquids, Gold™ AB Since a radiation has an extremely short penetration length
and Ultima Gold F, the a-peak resolution turned out to in water and solid substances, direct counting of a salt residue
be rather high (40 keV FWHM for 239Pu on LSC scale). This of dry ashed urine is not possible. Therefore, complex
allows the Tri-Carb with alpha/beta discrimination to be radiochemical techniques have been developed for efficient
used as a spectrometer for screening either transuranium separation of the transuranium elements from the bulk
nuclides with energies exceeding 5 MeV such as 239Pu, matrix.2,3 However, in addition to several purification steps,
241
Am, 244Cm or uranium isotopes between 4-5 MeV (238U, these methods require the production of almost weightless
236
U, 235U, 234U) in small counting windows of 120 keV each. planar sources (e.g., via electrolytic deposition) in order
Under these conditions, very low background count rates to perform radioassays with proportional or surface barrier
of 0.05 CPM are obtained in each window, resulting in a detectors.
high figure of merit (E2/B) of » 180,000 and a detection limit
In contrast to the extensive preparative techniques, fast
as low as 1.5 mBq/L (or 0.04 pCi/L) in a 500 minute count
methods using a/b-LSC are of increasing interest.4,5 Due to
interval.
the efficient detection of a emitters in a liquid scintillation
cocktail, extensive radiochemical purification procedures are
not necessary provided the sample is homogeneous in the
liquid scintillation cocktail. Although for a counting, liquid

scintillation detectors are mainly used only as gross analyzers, Methods and Materials
they are highly suitable for screening alpha activities in
Composition of the Actinide Resin
bioassay samples since low detection limits of a few mBq/L
34
U, 210Po or 226Ra from the U and Th decay Inc., Darien, Illinois, USA), is shown in Figure 1,
a blank sample. In obtained. This could be shown R = 2-ethylhexyl. pre-chromatographic sup- procedure described here is based on the
can be human urine, the activi- where using a simple The The separation
these natural α emitters chemistryrange actinide coprecipitationhas a nominal particle size strong affinity of the resin for actinides
concentration typically with port used in this study by extraordinarily
0.1 and 20 mBq/L,) mainly caused by 210Po performed using100-150 microns.
Ca3(PO4 2.6 A radioassay was distribution of PerkinElmer’s (particularly in the tri-, tetra- and hexavalent oxidation states),
a uptake with plant diet.9
low level model Tri-Carb with alpha/beta discrimination
The Separation Procedure
even from strongly acidic solutions.10 Actinide resin is com-
summarizes the typical range of activities discrimination radiochemical procedure is shown liquid extractant (containing a diphosphonic acid
equipped with highly efficient The schematic between a posed of a in
rresponding countradiation.7,8 However, the Figure 2. The individual steps will be explained group) coated onto a chromatographic support.
and b rates for α/β-LSC) for presence of anthropogenic functional in
t important natural α emitting nuclides in detail below. The extractant, trade named DIPEX™ (Eichrom Industries,
nuclides such as Pu, Am or Cm in urine using gross
239 241 244
nce typical blank count rates are as low as
M with thecountingTri-Carb 2550TR/AB,
Packard methods can be justified only oxidation of count
Partial if the a net the organic matter: 0.5 LIllinois, USA), is shown in Figure 1, where R =
Inc., Darien,
ribution from natural components signifi-
rate clearly exceeds those produced by decay of the naturally L glass beaker and The chromatographic support used in this study
urine is transferred into a 1 2-ethylhexyl.
xceeds reagent blank radionuclides such as 238U,mLU, 210Po or3 226Ra
occurring values. This reduces 100 234 65% HNO is added. The has a nominal particle size distribution of 100-150 microns.
beaker is then
ting sensitivity for screening anthropogenic covered with watch glass and gently boiled for two
from the In this work,decay series in a blank sample. In human
s in bioassay studies. U and Th Ra and Po
hours under infrared light. Subsequently, Separation Procedure
The the solu-
clides are urine, the activities of these natural has to cool down to room temperature.
automatically eliminated using tion a emitters typically
on chromatography without theand 20of
range between 0.1 need mBq/L, mainly caused by 210Po The schematic radiochemical procedure is shown in Figure 2.
purification steps. Sorption on actinide resin: 200 mg of actinide resin steps will be explained in detail below.
The individual
and Ra uptake with plant diet.
226 9
is added and the solution is stirred for four hours to
ds and Materials ensure sorption equilibrium (see Figure 3). oxidation of the organic matter: 0.5 L urine is trans-
Partial
Table 1 summarizes the typical range of activities (and
corresponding count rates for a/b-LSC) for the mostresin from the ferred into a 1 L glass beaker and 100 mL 65% HNO3 is added.
sition of the Actinide Resin Separation of the important solution: The
aration procedure described here nuclides in urine. Sinceof the resin containing the The beaker is then covered with watch glass and gently boiled
natural a emitting is based on separation typical blank actinides from
aordinarilycount rates areof the resin 0.1 CPM with of the solution with
strong affinity as low as for the bulk the Tri-Carb is obtained via filtration on under infrared light. Subsequently, the solution
for two hours
s (particularly in the tri-, tetra- and hexavalent 0.3 µm (25 mm diameter) WCN cellulose cool down to room temperature.
has to nitrate
n states), even from strongly acidic solu- contribution from natural Inc., Ann Arbor, Michi-
alpha/beta discrimination, the membrane filters (Whatman
Actinide resin is composedsignificantly exceeds reagent mounted on a 25 This glass frit membrane
components of a liquid extrac- gan, USA) blank values. mm Sorption on actinide resin: 200 mg of actinide resin is
taining a diphosphonic acid functional group)
reduces the counting sensitivity for screening anthropogenicrate, the filtration is
holder. To increase the filtration
nto a chromatographic support. The extrac- performed under a vacuum using a water and the solution is stirred for four hours to ensure
added pump.
de named actinides in bioassay studies. In this work, Ra and Po radio-
DIPEX™ (Eichrom Industries, sorption equilibrium (see Figure 3).
nuclides are automatically eliminated using extraction
chromatography without the need of further purification steps. Separation of the resin from the solution: The separation
of the resin containing the actinides from the bulk of the
solution is obtained via filtration on 0.3 μm (25 mm diameter)
WCN cellulose nitrate membrane filters (Whatman Inc.,
Ann Arbor, Michigan, USA) mounted on a 25 mm glass frit
membrane holder. To increase the filtration rate, the filtration
is performed under a vacuum using a water pump.

Table 1.
Table 1. Typical range of the activities of natural a emitting radionuclides in
human urine. of the activities of natural α emitting radionuclides in human urine.
Typical range

2

2

After filtration, the resin on the filter will show a
yellow color due to adsorption of some organic
substances during thethe resin onthe filterTheshow a yellow color
After After filtration, exposure process. will filtrate a
filtration, the resin on the filter will show
(solution)colorthen be removed. organicsome organic the
yellow can adsorption adsorption of substances during
due to due to of some
substances during the exposure process. Thethen be removed.
exposure process. The filtrate (solution) can filtrate
Stripping can then be removed.
(solution)of the reagent from the resin: Stripping
of the reagent from the inert support (polymeric
Stripping of the reagent from the resin: Stripping of the
substrate) isof the reagent from the(polymeric steps
Stripping performed in three consecutive
reagent from the inert support
resin: Stripping
substrate) is
using 5performed from thein each step. As in 5 mL isopropanol
mL isopropanolconsecutive steps using the
of the reagent
in three
inert support (polymeric
Figure 1.
Structure of the actinide resin. preceding step, the filtration three consecutive steps
substrate) is performed in is performed under a
in each step. As in the preceding step, the filtration is

Figure 1. Structure of the actinide 1.
vacuum5using a water a vacuumeach step. solutionThe organic
using performed under pump. The organic As in the
mL isopropanol in using a water pump.
Figure resin. will be yellow will (after dissolution dissolution of a
solution and be yellow and (afterof the reagent the reagent
Structure of the actinide resin. preceding step, the filtration is performed under
from its bed) the water pump. will beorganic solution support
vacuum using a substrate willThe white in color.The
from its bed) the substrate be white in color.
The support canbe discarded.
can then then be discarded.
will be yellow and (after dissolution of the reagent
from its bed) the of the solution for LSC: The organic solution is
Preparation substrate will be white in color.
Preparation of the solution for LSC: The organic
The support can into abe discarded.
transferred then 100 mL wideneck quartz glass flask and is
solution is transferred into a 100 mL wideneck quartz
glass flask and is taken to dryness on The organic
Preparation 65% HNO3 and 1for LSC: a heating 2SO4 is then
taken to dryness on a heating plate using additional infrared.
Five mL of the solution mL
plate using additional infrared. Fiveofwideneck quartz
solution is transferred into a the reagent.65% solution is gently
mL HNO3
concentrated H
added for oxidation of 100 mL
and 1 mL of concentrated H2SO4 is thenThea heating
added for
glass boiled and slowly evaporated to dryness until a
flask and is taken to dryness on
oxidation ofadditional infrared. solution is gently thoroughly
the reagent. The
plate using transparent residue is Five mL 65% HNO3is not
boiled clear,of concentrated H SO drynessIfadded a
and slowly evaporated to is then until for
obtained. the color
and 1 transparent, addition of 30% 4of H2O2 to the cooled residue
mL
thoroughly clear, transparent residue is obtained. If
2
oxidation of the reagent. The solution is dissolved in 2 mL
is helpful. The transparent residue is then gently
the color is not transparent, addition of 30% of H2O2
boiled0.5 M HCl.
and slowly evaporated to dryness until a
to the cooled residue is helpful. The transparent
thoroughly clear, transparent residue is obtained. If
residue is then dissolved in 2 mL 0.5 M HCl.
Cocktail transparent, addition scintillation 2O2
the color is notpreparation and liquid of 30% of Hcounting:
to theThe sample solutionis helpful. The transparent
cooled residue is transferred into a 20 mL plastic
Cocktailispreparation and 2liquid scintillation
residue then dissolved in mL 0.5 Mof Ultima Gold AB
scintillation vial containing a mixture HCl.
counting: The sample solution is transferred into a
20 mL plastic scintillation(5 mL). This mixture yields optimal a/b
(12 mL) and Gold F
vial containing a mixture
Cocktail preparation and and peakscintillation
pulse shape discrimination liquid resolution
of Ultima Gold AB (12 mL) and Ultima Gold Fof the a
counting: The Figure yields optimal α/β pulse
(5 mL). This(seesample 4). The vial istransferred into a and
pulses mixture solution is shaken until aqueous
20 mLorganic phases are mixed completely and a mixture solution
plastic scintillation vial containing the α
shape discrimination and peak resolution ofthe cocktail
pulses (see Gold AB (12 mL) about until Gold
of UltimaFigure a temperatureis shaken10 °C in a refrigerator.
is cooled to 4). The vial ofand Ultima aque- F
ous and organic mixtureare mixed completely and
(5 mL). This phases yieldscocktail must be checked for
Prior to measurement, the optimal α/β pulse
the cocktail separation and peak resolution of the transparent
shape phase solution is(solution must be homogeneous,α
discrimination cooled to a temperature of
about 10(see in a refrigerator. Prior to measurement,
pulsesand colorless); 4). The vialscintillation counting is performed
°C Figure finally liquid is shaken until aque-
the cocktail the Tri-Carb Alpha/beta discrimination and
ous and organic be checked mixed completelyoption in the
using must phases are for phase separation
(solution must be homogeneous, transparent and of
the cocktail solution is cooled to a temperature
a/b-mode.
colorless);°C in a refrigerator. Prior to measurement,
about 10 finally liquid scintillation counting is
the cocktail must be checked for phase separation
performed using the Tri-Carb 2550TR/AB in the
Results and Discussion
α/β-mode. must be homogeneous, transparent and
(solution
colorless); finally liquid of various experiments to is
A detailed description
scintillation counting study the
performed using the Tri-Carb 2550TR/AB in the
sensitivity of different chemical parameters, uptake capacity
Results andresin, and counting conditions can be obtained from
of the Discussion
α/β-mode.
Eikenberg, et al. 19

A detailed description of various experiments to
Results and Discussion
study the sensitivity of different chemical param-
eters, uptake capacity of the resin, and counting
conditions can be obtained from Eikenberg, et al.19 to
A detailed description of various experiments
study the sensitivity of different chemical param-
eters, uptake capacity of the resin, and counting
Figure 2. Schematic illustration of the fast procedure for
conditions can be obtained from Eikenberg, et al.19
Figure 2.
separation of actinides from urine.
Schematic illustration of the fast procedure for

Figure 2.
Schematic illustration of the fast procedure for
3

3 3

close to 100% at the crossover setting, high values
of 95% were still obtained at the higher (140 ns)
discriminator setting (see the “Analysis of Counting
Sensitivities” section).
value of 140 ns. While the counting efficiencies were
close to 100%of Th, Pa, U, Pu, Am, Cm: The chemical yield or
at the crossover setting, high values
value of 140 ns. While the counting efficiencies were
Recoveries
of 95% were stillTh, Pa, U,at the higher (140 chemi-
Recoveries of obtained Pu, Am, Cm: The ns) was
close to 100% at theacrossover radiochemical analysis
recovery following complete setting, high values
discriminatoror recovery the “Analysiscomplete radio-
cal yield setting (see following a of Counting
of determined from the addition of radiospikes of known
95% were still obtained at the higher (140 ns)
Sensitivities”analysis was determined from the addition
chemical section).
discriminator setting (seesample (Table 2). In particular, two
activity to a blank urine the “Analysis of Counting
of radiospikes of known activity to a blank urine
Sensitivities”studied to check on chemical recovery:
steps were section).
Recoveries of Th,2). In particular, two steps chemi-
sample (Table Pa, U, Pu, Am, Cm: The were stud-
cal yield check on chemicalyield oncomplete radio-
ied to or•recovery following a the resin
The adsorption recovery:
Recoveries of Th, Pa, U, Pu, Am, Cm: The chemi-
chemical analysisoverall (total) chemical recovery
• The was determined from the addition
cal yield adsorption yield on the a complete radio-
• The or recovery following to a
of radiospikes of known activityresin blank urine
chemical overall In particular, two from the addition
analysis was determined
• obtain the reproducibility of thesteps were spike
sample (Table 2). (total) chemical recovery all stud- experi-
ToThe results,
of radiospikes chemical recovery: to a blank urine
to check on of known activity
ied ments were repeated at least four times for each radio-
sample (Table 2). In particular, two steps were stud-
iedTo obtain on chemical recovery: results, all spike
to check the reproducibility of the
nuclide. The sorption yield on the resin was by means of
• The adsorptionwere repeated itself or via decay or ingrowth
experiments yield nuclide at least four times for
g-spectrometry of the on the resin
Figure 3. • The daughter(total) chemical recovery on the resin
of overall nuclides.The sorption yield
each radionuclide.
Kinetic uptake experiments: determination of sorption half-
• The adsorptionof γ-spectrometry of the nuclide itself
was by means yield on the resin
• Thevia2decay or ingrowth ofactinide resin has an extremely
Table clearly indicates that recovery all spike
or overall (total) chemical the results,
lives for U and Am.
To obtain the reproducibility of daughter nuclides.
experiments were repeated at least four times a very
strong affinity for all tested actinides even from for

Figure 3. each radionuclide. The sorption the results, allresin an
To strong 2the reproducibilitywith yield salt content (average
Table acidic urine solution that actinide the spike
obtain clearly indicates of high on resin has
Kinetic uptake experiments: determination of sorption half-
experiments strongrepeated2at all shows actinidesfor almost
salt contentwere affinity for least four times even
wasextremely of γ-spectrometry of tested that there is
by means 30 g/L). Table also the nuclide itself
Figure 3.
Figure 3. Kinetic uptake experiments: determination of sorption
lives for U and Am. or via decay orstrong acidic urine yield on for high salt
each radionuclide. The sorptionsolution with aresin
no differenceingrowth thedaughter yields the complete
from a very between of chemical nuclides.
halflives for U and Am.
Kinetic uptake experiments: determination of sorption half- was by means of γ-spectrometry ofThis means that additional
analysis and the adsorption yield. the nuclide itself
content (average salt content 30 g/L). Table 2 also
lives for U and Am. or via decay or ingrowthstripping, (ii) digestion and (iii)
chemical losses fromalmost daughter nuclides. an the
shows that there is (i) of actinide resin has
Table 2 clearly indicates thatno difference between
extremely strong affinity for all tested actinides even the
chemical yields for a complete analysis and
transfer into the liquid scintillation vial are insignificant.
Table very strong acidic urine solution withto routine
This 2 clearly indicatesbe easily adopted high chemi-
adsorption can hence that actinide resin has an
from a methodyield. This means that additional salt
contentlosses from (i) stripping, g/L). Table 2 even
extremely strongsalt contentall tested actinidesalso(iii)
laboratory use. affinity for 30 (ii) digestion and
cal (average
shows very strong acidic no difference between salt
from athat there is almosturine solution with highthe
chemical(averagefor acontent 30 g/L). Table 2 the
content yields salt complete analysis and also
adsorption yield. is almost no that additional chemi-
shows that there This means difference between the
cal losses from (i)for a complete analysisand (iii)
chemical yields stripping, (ii) digestion and the
adsorption yield. This means that additional chemi-
cal losses from (i) stripping, (ii) digestion and (iii)

Figure 4.
Smoothed liquid scintillation spectrum of 239Pu and 244Cm
obtained with Packard Tri-Carb 2550TR/AB.

Figure 4.
Figure 4. Smoothed liquid scintillation spectrum of 239Pu and 244Cm
Smoothed liquidYield Investigations Pu and 244Cm
Chemical scintillation spectrum of 239
obtained with PerkinElmer Tri-Carb 2550TR/AB.
Figure 4.
Direct spike experiments:
Chemical liquid scintillation spectrumThe Pu and 244Cm
Smoothed Yield Investigations of 239 counting efficien-
Direct spike experiments: The counting efficienciesspiked
cies were determined with radiolabeled were

Chemical Yieldradiolabeled spiked solutions to simulate
solutions added to cocktail mixtures added to
determined with Investigations
routine chemical analysis. The cocktails were mea- Table 2. Chemical recoveries obtained from a complete analytical
cocktail mixtures to simulate routine chemical analysis. The Table 2.
Chemicaleach under two different discriminator set-
sured Yield Investigations counting efficien-
Direct spike experiments: under two different discrimi-
cocktails were measured each The
procedure.
Chemical recoveries obtained from a complete analytical
cies werei.e., i.e., at the crossover point (125ns) and at a
tings, determined with radiolabeled spiked
nator settings,
at the crossover point (125
ns) and at a
procedure.
Direct spike experiments: The counting simulate efficien-
solutions addedWhilecocktail mixtures to were close
value of 140 ns.
to the counting efficiencies
routine chemical analysis. The radiolabeled spiked
cies were the crossover setting,cocktails were95% were
determined with high values of mea-
to 100% at Table 2.
sured each underto cocktail mixtures to simulate
solutions added two different discriminator set- 4
Chemical recoveries obtained from a complete analytical
still obtained at the higher (140 ns) discriminator setting
tings, i.e., at the crossoverThe cocktails were mea-
routine chemical analysis. point (125 ns) and at a procedure.
(see the “Analysis of Counting Sensitivities” section). Table 2.
sured each under two different discriminator set- Chemical recoveries obtained from a complete analytical
tings, i.e., at the crossover point (125 ns) and at a procedure.
4

4
4

All experiments wereliquid scintillation vial are insignifi-
transfer into the performed with 200 mg resin per
0.5 cant. This method can hence be at least adopted to
L sample and an extraction time of easily four hours
(for routine studies see the following section entitled
kinetic laboratory use.
“Experiments on Uptake Kinetics”). Under these conditions
All experiments were performed with 200 mg resin
only about 75% Am was consistently recovered, whereas
the per 0.5 L of most of thean extraction time of at least
recoveries sample and investigated actinides exceeded
90%. This discrepancy is most studies see the fact that the
four hours (for kinetic likely due to the following
resin uptake coefficient for Am(III) more rapidlyKinetics”).
section entitled “Experiments on Uptake decreases
with aciditythese conditions only about 75% in thewas
Under compared to those actinides present Am
tetra- or hexavalent state suchwhereas the recoveries10of
consistently recovered, as Th(IV), Pu(IV) or U(VI).
most of the investigated actinides exceeded 90%.
Recovery of Ra: In contrast to the actinides, the uptakethe
This discrepancy is most likely due to the fact that of
Ra on actinide resin was found to beAm(III) more rapidly
resin uptake coefficient for less than 5% (Table 2).
Thisdecreases with acidity compared to those actinides
result is consistent with the low sorption coefficients
(k'-values) for the tetra- or elements (Ca2+ and Ra2+ in
present inthe alkaline earthhexavalent state such )as
strong acidicPu(IV) or U(VI).
Th(IV), medium as obtained by Horwitz, et al.10 Even
10

in the presence of 2 M HCl solutions containing 1 M CaCl2,
the Recoverythe least efficiently sorbed species Am(III) the
uptake of of Ra: In contrast to the actinides, Figure 5. Bar chart showing the chemical recoveries obtained from two
Figure 5.
remained considerably high (k' resin was foundisto be less
uptake of Ra on actinide = 103). Since k' lower for different resin additions.
Bar chart showing the chemical recoveries obtained from
Ra2+than 5% 2+ (k' <1), and average urine Ca/Ra ratios are
than Ca (Table 2). This result is consistent with the two different resin additions.
extremely high, no additions of(k'-values) for the alkaline
low sorption coefficients Ca or Ba carrier are required Experiments on uptake kinetics: To obtain the times
for earth elements (Ca and Ra ) in strong acidic
2+ 2+
a routine analysis. required for sorption equilibrium at a steady state, the
medium as obtained by Horwitz, et al.10 Even in the uptake kinetics were studied kinetics: To obtain the
Experiments on uptake for tri- and hexavalent species
Recovery of Po:2Because solutions containing 1 M CaCl2,
presence of M HCl oxidation of the stripped reagent using Am(III) andfor sorptionsolutions. For thesesteady
times required U(VI) tracer equilibrium at a investiga-
fraction uptake of the least efficiently sorbed species/
the is performed under high temperatures using HNO3 state, the uptake kinetics were studied for tri- and
tions, aliquots were prepared as explained in the previous
H2SO4 mixtures (boiling point of sulfuric acid = (k' = 10 3).
Am(III) remained considerably high 338 ˚C), the hexavalent species using Am(III) and U(VI) tracer
section. This time, however, aliquots were spiked with
second naturally lower forcomponent 210Po is(k' <1), and
Since k' is occurring Ra2+ than Ca2+ efficiently solutions. For these investigations, aliquots were
identical activity concentrations and the extraction was inter-
average urine Ca/Ra ratios are extremely high, no
eliminated since under acidic conditions at elevated prepared as explained in the previous section. This
rupted at times given in Figure 3. Very rapid uptake was
temperatures, Po (probably present as are required for a is
additions of Ca or Ba carrier Po-oxide in the ash) time, however, aliquots were spiked with identical
routine analysis.
volatile. Tracer experiments with 209Po(NO3)4 spike solutions activity concentrations and the extraction was
observed and in about two hours steady state conditions

indeed revealed repeatedly no detectable activity in the interrupted at times given in Figure 3. Very rapid
were obtained independently of the amount of added resin.

liquid scintillation Po: Because oxidation of the stripped
Recovery of cocktail. uptake was observed and in about two hours steady
If the sorption process follows first order kinetics, the data
reagent fraction is performed under high tempera- state conditions were obtained independently of the
should plot on a straight line in a semi-log diagram with the
Uptake studies HNOdifferentmixtures (boiling point of
tures using with 3/H2SO4 resin additions: As dis- amount of added resin.
remaining activity in solution plotted versus the exposure
cussed above, the= 338 °C), the second naturally occur-
sulfuric acid uptake coefficient of Am(III) decreases time (Figure 3). In this case the sorption exponent ksorp can
rapidly with acidity. Therefore, slight neutralization ofsince
ring component 210Po is efficiently eliminated the If the sorption process follows first order kinetics,
be extracted from the relation:
aqueous samples with NH4OH elevated the oxidation step
under acidic conditions at(following temperatures, Po the data should plot on a straight line in a semi-log
(probably present as Po-oxide in the ash) is volatile.
with HNO3) was attempted. However, when adding NH4OH diagram with the remaining activity intsolution plot-
asolution = e – ksorp •
to reduce the acidity of the solution from)4 spike to 1 M
Tracer experiments with 209Po(NO3 ≈ 2 M solutions ted versus the exposure time (Figure 3). In this case
indeed revealed repeatedly no detectable activity in
HNO3, the solutions became black and opaque. An improved (with asolution = activity in ksorp can be extracted from the
the sorption exponent solution) and via regression analysis
the liquid scintillation cocktail.
technique to obtain a higher extraction yield is simply to relation: A more comprehensive approach is the use of
of the data.
the sorption half-lives (i.e., T1/2 = ln2/k). Very short half-lives
a =e
increase the amount of actinide resin per same sample
-ksorp . t
volume. The studies with different resin additions: As
Uptake results for additions of 0.4 g/L and 1 g/L are solution
of only eight and 20 minutes were calculated for U and Am,
discussed above, the uptake coefficient of Am(III)
depicted in Figure 5. Almost quantitative extraction for all respectively using this approach.
the decreases rapidly withwhen taking 1 g/L actinide resin.
actinides were obtained acidity. Therefore, slight neu- (with a solution = activity in solution) and via regression
tralization of the aqueous samples with NH4OH analysis of the data. A more comprehensive
(following the oxidation step with HNO3) was at- approach is the use of the sorption half-lives
tempted. However, when adding NH4OH to reduce (i.e., T1/2 = ln2/k). Very short half-lives of only eight
the acidity of the solution from ≈ 2 M to 1 M HNO3, and 20 minutes were calculated for U and Am,
the solutions became black and opaque. An im- respectively using this approach.
proved technique to obtain a higher extraction yield
is simply to increase the amount of actinide resin per
same sample volume. The results for additions of
0.4 g/L and 1 g/L are depicted in Figure 5. Almost
quantitative extraction for all the actinides were
obtained when taking 1 g/L actinide resin.

5
5

Table 3.
Set of values used for the calculation of the LLDs for 239Pu.

The set of parameters used for the calculation of the
Figure 6. LLD is given in Table 3. The other parameters were
α/β crossover curves as function of PDD setting obtained
with 241Am and 36Cl. kept either constant (i.e., Vs = 0.5 L) or were not
relevant (µ). However, it has to be noted that in
contrast to procedures based on LSC, µ can only be
Analysis of Counting Sensitivities omitted when almost weightless sample discs are
produced. If that is not the case, absorption of α
Optimum α/β discriminator settings: For gross radiation in the sample source itself has to be
α/β counting systems, two parameters are essential considered seriously.
to determine the sensitivity of a radioassay: back- Table 3.
ground count rate (B) and counting efficiency (E), Set of values used three methods arethe LLDs for 239two proce-
In Figure 7, for the calculation of compared; Pu.
which can be expressed as figure of merit or E2/B.20 dures based on α/β-LSC (previous work of Eikenberg,
To reduce background scatter, misclassification of β et al.)6 and a method2 developed for low level gas-
Table 3.
pulses counted as α has been minimized by optimiz-The set of3.parametersthe calculation(GPC). the LLDs for 239Pu.
Set of values used for used for forcalculation of Although a very
flow proportional counting of the LLDs for ofPu.
Table Set of values used the the calculation 239 the
Figure afterpulse analysis featuresLLDlow background count Tableparameters CPM was
ing the pulse decay and 6. is given in Table 3. Therate of 3. of0.04LLDs for 239Pu.
other only were
Set of values used for the calculation the
the Packard Tri-Carb 2500TR/AB. As shownkept either constant (i.e., Vs = 0.5 L) or were not
ofAm and 36Cl.
with 241
7,8

in Figure 6, low α and β misclassification (0.6%)relevant (µ). However,used forto be noted that in
The set of parameters it has the calculation of the
resulted atCl. optimum pulse decay discriminatorcontrast to procedures based on LSC, µ can onlywere
the Figure 6.
Figure 6. a/b crossover curves as function of PDD setting obtained
LLD is given in Table 3. The other parameters be
Analysis ofandcurvesof 125. Optimum E2/B values were,omitted when almost weightless 0.5 L) or were not of the
kept either constant (i.e., Vs = sample calculation
The set of parameters used for the discs are
with 241Am and 36
(PDD) setting as function of PDD setting obtained
α/β crossover
Counting Sensitivities
with 241Am 36
Cl. Figure 6. higher PDD settingproduced. (µ). However,the hasThebe noted thatαin were
however, obtained for a slightly relevant is given in Table case, absorption of
LLD If that is not it 3. to other parameters
Analysis of 36discriminator spill (0.1%) is extremelyradiation to procedures based on LSC, µhasL) or be
with of Am α/β this value, the β settings:
241140. At
Optimum andCounting Sensitivities For gross
Cl. contrast in the constant (i.e., Vs = 0.5 only were not
kept either sample source itself can to be
α/β counting systems, two parameters the α backgroundconsidered seriously. weightlesshas to be noted that in
low (hence significantly reducing
Optimum a/b discriminator settings: are essential
Analysis of Counting Sensitivities For gross a/b relevant (µ). However, it sample discs are
omitted when almost
tocounting systems, two the loss in counting efficiency due produced. If to procedures based absorption of αonly be
determine thewhile parameters radioassay: back-
count rate), sensitivity of a are essential to determine contrast that is not the case, on LSC, µ can
ground counting some and counting is minimal.(E), (b) In Figure 7, three methods are compared; two proce-discs are
Analysis ofα/β a (B) α pulses as β efficiency rate
the to count ratediscriminator settings: For
Optimum Counting Sensitivities count gross
sensitivity of radioassay: background radiation in when almost weightless sample be
omitted the sample source itself has to
α/β countingexpressed as which can be are E2/B.20
whichcountingefficiency (E),figure of merit or essentialfigure produced. If that is not the case, absorption of α
and can be systems, two parameters expressed as dures based on α/β-LSC (previous work of Eikenberg,
considered seriously.
To reduceor E2/B.20discriminatora settings: Forlimit ofet al.)6 and a method2 developed for low level gas- to be
of merit background scatter, misclassification of gross
to determine the To reduce background scatter, back-
Comparison sensitivity of radioassay: misclas-
Optimum α/β of detection limits: The lower β radiation in the sample source itself has
pulses counted(LLD)countedminimized by optimiz- by flow proportional counting (GPC). Although a proce-
sification of b pulses(B)been counting been are essential
detection as α has the as a has efficiency (E),
ground countsystems,and 95% confidence probability In Figure 7, three methods are compared; two very
rate at two parameters minimized
α/β counting considered seriously.
ing the pulsebecalculated from analysis ofanalysis2sampleslow background count rate of only 0.04 CPM was
which can the expressed as figure analysis features 20
decay and afterpulse of merit or E /B.
level was pulse decay and blank back-
determine the sensitivity of a radioassay:features dures based on α/β-LSC (previous work of Eikenberg,
tooptimizing background scatter,afterpulse As shown β
ofof thePackardequation as2500TR/AB.
theusing the Tri-Carb given by Seymour, et al.:21
To reduce discrimination.7,8 Asof
misclassification shown
7,8
ground Tri-Carb rateα(B) and counting efficiency (E), et al.) Figuremethod methods are compared;gas-
and a developed for low level
6 2
count with alpha/betaminimized by (0.6%)
inpulses counted as and b β misclassification optimiz- 20 flow proportional counting (GPC). Although a very proce-
Figure 6, low a and misclassification (0.6%) resulted at
low α has been In 7, three two
in Figure 6, expressed as figure of merit or E2/B.
which can be optimum afterpulse analysis features
ing the pulsepulse decay discriminator (PDD) setting of 125.lowdures based on α/β-LSC (previous work ofwas
resulted at the decay andpulse decay discriminator background count rate of only 0.04 CPM Eikenberg,
(PDD) setting of Tri-Carb 2500TR/AB.7,8 As were, of β
To reduce background scatter, misclassification et al.)6 and a method2 developed for low level gas-
the optimum
of the Packard 125. Optimum E2/B values for a slightly shown
however, obtained forhas been minimized by(0.6%)
pulses counted as α and βhowever, obtainedsetting
in Figure 6, low α a slightly higher PDD optimiz-
Optimum E /B values were,
flow proportional counting (GPC). Although a very
2
misclassification
of 140. At at the optimum afterpulse analysis features
ing the pulse decay thestatistical valueis extremely
resulted this value, and pulse(0.1%) discriminator
where (K) = 1.64 = β spill decay for a confidence
higher PDD setting of 140. At this value, the b spill (0.1%)
low background count rate of only 0.04 CPM was
lowthe Packard95%; (IsignificantlyE2/Bbackground in
of (hence significantly 0reducing the α values counts
(PDD) setting of 125. Optimum background were,
interval of Tri-Carb=2500TR/AB.7,8the ashown
is extremely low (hence
) total reducing As back-
induetime t; obtained for apulses as b = chemical recovery;
Figure while the andslightly ) is minimal. (0.6%)
count rate),6, low αwhiletime; (Yihigher PDD setting
however, (t) = counting in counting efficiency due
ground count rate), loss the loss in counting efficiency
β misclassification Figure 7. Evolution of the lower limit of detection for three methods
Figure 7.
toof 140.countingvalue, detector efficiency; (Vs) = sample
(E) =at this optimum as β is minimal.
resulted
to counting or
counting somesome a βpulse(0.1%) is extremely
At the α pulses spill decay discriminator
the based on GPC and LSC.
Evolution of the lower limit of detection for three methods
lowvolume;significantly reducing coefficient.of detection
(hence and (µ) = attenuation lower values were,
(PDD) setting of 125. Optimumthe2/Bbackground
Comparison of detection limits: The E
α limit based on GPC and LSC.
countat the 95% confidence probability efficiencycalculated
rate), while the lossslightly higher PDD setting
in countinglower limit due
Comparison of detection limits: The level was of
however, obtained for a
(LLD)
detection (LLD)value,samples usingminimal. extremely
offrom analysissome α pulses confidence equation as given 6
to counting
140. At this blank the βas β is(0.1%) is
of
at the 95% spill the probability
levelSeymour, et al.21 from analysis of blank samples
was calculated
low (hence significantly reducing the α background
by
using the equation as given limits: The lower limit of
Comparison of detection by Seymour, et al.:21
count rate), whileat the 95% confidence probability
detection (LLD)
the loss in counting efficiency due
to counting some α pulses as β isof blank samples
level was calculated from analysis minimal.
using the equation as given by Seymour, et al.:21
Comparison of detection limits: The lower limit of
where (K) = 1.64 =at the 95% confidence probability
detection (LLD) statistical value for a confidence
interval of calculated= totalanalysis of blank samples
95%; (I 0) from background counts in
level was = 1.64 = statistical value for a confidence interval
time t; the equation time; (Yi) = chemical recovery;21 of
where (K) counting
(t) =
using (I ) = total as given by Seymour, et al.: Figure 7.
(E) = counting orbackground counts in for sat;=(t) = counting Evolution of the lower limit of detection for three methods
where (K) = 1.64 = statistical value time ) confidence
95%; 0 detector efficiency; (V sample
volume; and chemical 0recovery; (E) = counting counts in
intervali)of 95%; attenuation coefficient. or detector based on GPC and LSC.
time; (Y = (µ) = (I ) = total background
time t; (t) = counting time; (Yi) = chemical recovery;
efficiency; (Vs) = sample volume; and (μ) = attenuation
Figure 7.
(E) = counting or detector efficiency; (Vs) = sample
coefficient.
Evolution of the lower limit of detection for three methods
volume; and (µ) = attenuation coefficient. 6 based on GPC and LSC.
where (K) = 1.64 = statistical value for a confidence
interval of 95%; (I 0) = total background counts in
time t; (t) = counting time; (Yi) = chemical recovery;
6 Figure 7.
(E) = counting or detector efficiency; (Vs) = sample Evolution of the lower limit of detection for three methods 6
volume; and (µ) = attenuation coefficient. based on GPC and LSC.

Thetaken to calculate the for the using low of the GPC
set of parameters used LLD calculation level
LLDcounters, the new3. The other parameters were kept
is given in Table procedure based on • /• -LSC yields
• •
either constant (i.e., Vs = LLD values. Thisrelevant is the
considerably lower 0.5 L) or were not result (μ).
However, it has toof the very high counting efficiencies
consequence be noted that in contrast to procedures
based onchemical recoveries. If,whenparticular, LSC
and LSC, μ can only be omitted in almost weightless
sample discs are produced. a that is not the case, absorption
is carried out using If small window for analysis
of a radiation in the sample source itself has tothe considered
of a special group of actinides (see be “• • peak
resolution and liquid scintillation quench” paragraph
seriously.
below), the background decreases to values about
0.05 7, three methods an extraordinary procedures
In FigureCPM. This yieldsare compared; two high figure
based merit (E2/B) of 180,000 of Eikenberg, et limit of
of on a/b-LSC (previous work or a detection al.)6 and
a method2 developed for minute counting proportional
1.5 mBq/L in a 500 low level gasflow interval.
counting (GPC). Although a very low background count
rate of onlyresolutionwas taken toscintillation quench:
• •peak 0.04 CPM and liquid calculate the LLD
using is well known counters, theresolution using LSC on
It low level GPC that • •peak new procedure based is
poor in comparison to • • spectrometry and hence
a/b-LSC yields considerably lower LLD values. This result is
the•consequence of the very high countinggross counters.
•• •LSC systems are used mainly as efficiencies and
-
chemical recoveries.if • • particular, LSC is carried out
Nevertheless, If, in pulse stretching scintillators
using a used, window for analysis of a special keV can be
are small FWHM values of 300-400 group of
actinides (see the “a peak resolution and procedure, a near
obtained.22 Since, for the current liquid scintillation
quench” paragraph below), the is prepared,decreases to
organic cocktail mixture background the • • peak Figure 8. Relations between Figure 8.
the true emission energy and liquid

resolution becomes fairly high (400 keV or 40 keV
scintillation quenched a energies of actinides.
Relations between the true emission energy and liquid
values about 0.05 CPM. This yields an extraordinary high scintillation quenched • •energies of actinides.
figure of merit (Escintillation scale).detection limit of
on a liquid 2/B) of 180,000 or a This allows peak
1.5separation 500 minute counting interval. as shown in
mBq/L in a between U and 238U or,
234
It is interesting to note, that for a set of a emitters with
Figure 4, between transuranium nuclides such as different energies, the ratio between both energy scales is
a peak resolution and • = 600 keV). Two observations
Pu and 244Cm (• E electronic assignment the a given energy to the mul- to
highly linear. Although of aqueous cocktail is quenched
239
liquid scintillation quench: It is well
known thatinterest.resolution using LSC are symmetrically
are of a peak First, the peaks is poor in comparison tichannel analyzer (MCA). Indeed stability tests
a higher degree, regression analyses yielded identical slopes
shaped and simple Gaussian-based fitting proce-
to a spectrometry and hence a/b-LSC systems are used using 239Pu spiked cocktails revealed identical there is
of exactly 10 (see Figure 8). This also implies that peak
mainly as (without additional terms for peak tailing) are
dures gross counters. Nevertheless, if a pulse stretching positions which scattered less assignment of a given
almost no drift for the electronic then 15 keV on the
scintillators are used, FWHM overlapping peaks. Second,
sufficient for fitting of values of 300-400 keV can be liquid scintillation scale for samples produced within
energy to the multichannel analyzer (MCA). Indeed stability
obtained.22 Since, for the current procedure, a using LSC
there is a significant shift of the • •energy near organic one year. This fact is helpful torevealed identical peak
tests using 239Pu spiked cocktails
distinguish between
cocktail mixture is prepared, emission energy.
with respect to the real the a peak resolution becomes two major groups of actinides which are of interest
positions which scattered less then 15 keV on the liquid
fairly high (400 keV or 40 keV on a liquid scintillation scale).
for in vitro measurements. As shown in Figure 8, all
anthropogenic transuranium nuclides are character-
scintillation scale for samples produced within one year. This
This allows peak phenomenon is due 234U and 238U or, as
This shifting separation between to ionization quench
ized is helpful to distinguish between twocompared to of
fact
by emission of higher • •energies major groups
shown in Figure • •particles dissipate their energysuch a
because the 4, between transuranium nuclides over
all natural uranium isotopes (i.e., 234U, 235U, 238U).
actinides which are of interest for in vitro measurements. As
as 239Pu and 244Cm (DE = causing less excited niveaus in
very small distance 600 keV). Two observations are
the orbitals of the scintillator targets.23 However, the For in in Figure 8, all anthropogenic transuranium nuclides
shown vitro screening, a distinction between these
of interest. First, the peaks are symmetrically shaped and
shift in energy from quenching remains constant for groups is often reasonable. For higher a energies compared
are characterized by emission of instance, monitoring
simple Gaussian-based fitting procedures (without additional
a fixed cocktail mixture. The relation between the of employees involved in uranium mining should For in
to all natural uranium isotopes (i.e., 234U, 235U, 238U). be
terms for peak tailing) are sufficient for fitting of overlapping
true • •emission energy and the liquid scintillation limited to uranium isotopes, whereas in nuclear
vitro screening, a distinction between these groups is often
peaks. Second, there is a significant shift of the a energy
quenched output is demonstrated in Figure 8 for the reprocessing plants or hot laboratories handling spent
reasonable. For instance, monitoring of employees involved
procedure given here and an aqueous cocktail. It is
using LS with respect to the real emission energy. 6 fuel elements, radiation hazards may arise predomi-
in uranium mining should be limited to uranium isotopes,
nantly from incorporation of 239Pu, 240Pu, 241Am and
This shifting phenomenon is for to ionization quench
interesting to note, that due a set of • •emitters with whereas in nuclear reprocessing plants or hot laboratories
different energies, the ratio between both energy handling spent fuel instead ofradiation hazards • •over
244
Cm. Therefore, elements, counting gross may arise
because the a particles dissipate their energy over a very
scales is highly linear. Although the aqueous cocktail predominantly of energy, a small 239Pu, 240 of only
a wide range from incorporation of windowPu, 241Am and
small distance causing less excited niveaus in the orbitals of
is quenched to a higher degree, regression analyses 120 keV can beinstead of counting gross a uranium
244
Cm. Therefore, taken for the group of over a wide
the scintillator targets.23 However, the shift in energy from
yielded identical slopes of exactly 10 (see Figure 8). isotopes energy, a small window of only 120 transura-
range of (160-280 keV) as well as for the keV can be
quenching remains constant for a fixed cocktail mixture. The
This also implies that there is almost no drift for the nium nuclides (260-380 keV).isotopes (160-280 keV) as
taken for the group of uranium
relation between the true a emission energy and the liquid
well as for the transuranium nuclides (260-380 keV).
scintillation quenched output is demonstrated in Figure 8
for the procedure given here and an aqueous cocktail.6

7
7

Conclusions 9. Shiraishi, K., Yamamoto, M., Yoshimizu, K., Igarashi, Y.
A fast and very efficient radiochemical procedure for screening and Ueno, K. (1994) Health Phys. Vol. 66, 30-35.
a activities in urine was developed based on sorption using
10. Horwitz, E.P., Chiarizia, R. and Diez, M.L. React. Funct.
an actinide extractive resin. A high figure of merit (180,000)
Polymers (in press).
is obtained by performing the radioassay with a Tri-Carb
with the Alpha/beta discrimination option. A low detection 11. Wrenn, et al., J. Rad. Nuc. Chem. Art. 156 (1992)
limit of 1.5 mBq/L (0.04 pCi/L) can be obtained in about 407-412.
eight hours counting time. This allows an annual throughput
of about 1,000 samples for screening a activities in urine. 12. Karpas, et al., Health Phys. 71 (1996) 879-885.
A complete analysis requires the use of only 0.5 L samples,
13. Dang, et al., Health Phys. 57 (1989) 393-396.
additions of only 0.2 g resin and can be terminated within
one day. 14. Dahlheimer and Henrichs, Rad. Prot. Dos. 53 (1994)
207-209.
References
15. Fisenne, et al., Health Phys. 53 (1987) 357-363.
1. Int. Com. Radiological. Protection. ICRP Publication 54,
Ann. ICRP Vol. 19 (1988). 16. ICRP Publication. 23 (1975).
2. Eakins, J.D. and Gomm, P.J. (1968) Health Phys. 14, 17. Shiraishi, et al., Health Phys. 66 (1994) 30-35.
461-472.
18. Fellmann, et al., Health Phys. 57 (1989) 615-621.
3. Horwitz, E., Ph Dietz, M.L., Nelson, D.M., LaRosa, J.J.
and Fairman, W.D. (1990) Anal. Chim. Acta Vol. 238, 19. Eikenberg, J., Zumsteg, I., Ruethi, M., Bajo, S., Fern, M.
263-271. J. and Passo, C.J., J. Radact. Radiochem. (in press).

4. Salonen, L. (1993) Sci. Tot. Environ. Vol. 130/131, 23-35. 20. Currie, L. A. (1968) Anal. Chem. 40, 586-593.

5. Bickel, M., Möbius, S., Kilian, F. and Becker, H. (1992) 21. Seymour, R., Sergent, F., Knight, K. and Kyker, B. (1992)
Radiochim. Acta Vol. 57, 141-151. Radioact. Radiochem. 3, 14-27.

6. Eikenberg, J., Fiechtner, A., Ruethi, M. and Zumsteg, I. 22. Yu, Y.F., Salbu, B., Bjornstad, H.E. and Lien, H.J. (1990)
Liquid Scintillation Spectrometry 1994, Radiocarbon Radioanal. Nucl. Chem. Lett. 145, 345-353.
1996, 283-292.
23. Horrocks, D. (1974) Academic Press. New York-London
7. Passo, C.J. and Kessler, M.J. (1992) Packard Instrument 346.
Company Publication, Report PBR0012, 8.

8. Passo, C.J. and Kessler, M.J. Liquid Scintillation
Spectrometry 1992, Radiocarbon 1993, 51-57.

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Application Note: A Rapid Procedure for Screening Transuranium Nuclides in Urine Using Actinide Resin and Low Level

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Application Note: A Rapid Procedure for Screening Transuranium Nuclides in Urine Using Actinide Resin and Low Level