EPA 402-R-10-001 d
www.epa.gov/narel
October 2011
Revision 0.1
Rapid Radiochemical Method for
Total Radiostrontium (Sr-90) In Water
for Environmental Remediation Following
Homeland Security Events
U.S. Environmental Protection Agency
Office of Air and Radiation
Office of Radiation and Indoor Air
National Air and Radiation Environmental Laboratory
Montgomery, AL 36115
Office of Research and Development
National Homeland Security Research Center
Cincinnati, OH 45268
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/90,
Total Radiostrontium ( Sr) in Water: Rapid Method for High-Activity Samples
Revision History
Revision 0
Revision 0.1
Original release.
• Corrected typographical and punctuation errors.
• Improved wording consistency with other methods.
• Corrected specification of analytical balance (6.1) to 10^-g
readability.
• Added pH paper to list of equipment and supplies (6.6).
• Added equations in 12.1 .6 that allow theoretical calculation of
the MDC and critical level for different decision error rates.
• Updated footnote 3 to further clarify origin of critical value
and minimum detectable concentration formulations.
• Updated rounding example in 12.3.2 for clarity.
• Deleted Appendix C (composition of Atlanta tap water) as
irrelevant
02/23/2010
10/28/2011
This report was prepared for the National Air and Radiation Environmental Laboratory of the Office of
Radiation and Indoor Air and the National Homeland Security Research Center of the Office of Research
and Development, United States Environmental Protection Agency. It was prepared by Environmental
Management Support, Inc., of Silver Spring, Maryland, under contracts 68-W-03-038, work assignment 43,
and EP-W-07-037, work assignments B-41 and 1-41, all managed by David Carman. Mention of trade
names or specific applications does not imply endorsement or acceptance by EPA.
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TOTAL RADIOSTRONTIUM (SR-90) IN WATER:
RAPID METHOD FOR HIGH-ACTIVITY SAMPLES
1. Scope and Application
1.1. The method will be applicable to samples where the source of the contamination is
either from known or unknown origins. If any filtration of the sample is performed
prior to starting the analysis, those solids should be analyzed separately. The results
from the analysis of these solids should be reported separately (as a suspended activity
concentration for the water volume filtered), but identified with the filtrate results.
1.2. The method provides a very rapid non-radioisotope-specific screen for total
radiostrontium in drinking water and other aqueous samples.
1.3. This method uses rapid radiochemical separations techniques for the determination of
beta-emitting strontium radioisotopes in water samples following a nuclear or
radiological incident. Although this method can detect concentrations of 90Sr on the
same order of magnitude as methods used for the Safe Drinking Water Act (SDWA),
this method is not a substitute for SDWA-approved methods for radiostrontium.
1.4. The method is capable of satisfying a required method uncertainty for 90Sr (total as
90Sr) of 1.0 pCi/L at an analytical action level of 8.0 pCi/L. To attain the stated
measurement quality objectives (MQOs) (see Step 9.2), a sample volume of
approximately 500 mL and a count time of approximately 1.25 hours are
recommended. The sample turnaround time and throughput may vary based on
additional project MQOs, the time for analysis of the final counting form and initial
sample volume. The method must be validated prior to use following the protocols
provided in Method Validation Guide for Qualifying Methods Used by Radiological
Laboratories Participating in Incident Response Activities (EPA 2009, reference 16.3).
1.5. This method is intended to be used for water samples that are similar in composition to
drinking water. The rapid 90Sr method was evaluated following the guidance presented
for "Level E Method Validation: Adapted or Newly Developed Methods, Including
Rapid Methods" in Method Validation Guide for Qualifying Methods Used by
Radiological Laboratories Participating in Incident Response Activities (EPA 2009,
reference 16.3) and Chapter 6 of Multi-Agency Radiological Laboratory Analytical
Protocols Manual (MARLAP 2004, reference 16.4). Multi-radionuclide analysis using
sequential separation may be possible.
1.6. This method is applicable to the determination of soluble radiostrontium. This method
is not applicable to the determination of strontium isotopes contained in highly
insoluble particulate matter possibly present in water samples contaminated as a result
of a radiological dispersal device (RDD) event.
1.7. Sequential, multi-radionuclide analysis may be possible by using this method in
conjunction with other rapid methods.
2. Summary of Method
2.1. Strontium is isolated from the matrix and purified from potentially interfering
radionuclides and matrix constituents using a strontium-specific, rapid chemical
separation method. The sample is equilibrated with strontium carrier, and concentrated
by Sr/BaCOs coprecipitation. If insoluble residues are noted during acid dissolution
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steps, the residue and precipitate mixture is digested in 8 M HNCb to solubilize
strontium. The solution is passed through a Sr-Resin™ extraction chromatography
column1 that selectively retains strontium while allowing most interfering radionuclides
and matrix constituents to pass through to waste. If present in the sample, residual
plutonium and several interfering tetravalent radionuclides are stripped from the
column using an oxalic/nitric acid rinse. Strontium is eluted from the column with 0.05
M HNOs and taken to dryness in a tared, stainless steel planchet. The planchet
containing the strontium nitrate precipitate is weighed to determine the strontium yield.
2.2. The sample test source is promptly counted on a gas flow proportional counter to
determine the beta emission rate, which is used to calculate the total radiostrontium
activity.
2.2.1. This test assumes that it is reasonable to assume the absence of 89Sr in the
sample. In such cases, a total radiostrontium analysis will provide for a specific
on
determination of Sr in the sample. The same prepared sample test source can
be recounted after -1-21 days to verify the total radiostrontium activity. If the
initial and second counts agree, this is an indication that 89Sr is not present in
significant amounts relative to 90Sr (within the uncertainty of the measurement).
OQ
2.2.2. Computational methods are available for resolving the concentration of Sr and
on
Sr from two sequential counts of the sample. An example of an approach that
has been used successfully at a number of laboratories is presented in Appendix
B to this method. It is the responsibility of the laboratory, however, to validate
this approach prior to its use.
3. Definitions, Abbreviations, and Acronyms
3.1. Analytical Protocol Specification (APS). The output of a directed planning process that
contains the project's analytical data needs and requirements in an organized, concise
form.
3.2. Analytical Action Level (AAL). The term analytical action level is used to denote the
value of a quantity that will cause the decisionmaker to choose one of the alternative
actions.
3.3. Analytical Decision Level (ADL). The analytical decision level refers to the value that
is less than the AAL based on the acceptable error rate and the required method
uncertainty.
3.4. Discrete Radioactive Particles (DRPs or "hot particles"). Particulate matter in a sample
of any matrix where a high concentration of radioactive material is contained in a tiny
particle (um range).
3.5. Multi-Agency Radiological Analytical Laboratory Protocol Manual (see Reference
16.4.)
3.6. Measurement Quality Objective (MQO). MQOs are the analytical data requirements of
the data quality objectives and are project- or program-specific. They can be
1 Sr-Resin™ is a proprietary extraction chromatography resin consisting of octanol solution of 4,4'(5')-bis (t-butyl-
cyclohexano)-18-crown-6-sorbed on an inert polymeric support. The resin can be employed in a traditional
chromatography column configuration (gravity or vacuum) or in a flow cartridge configuration designed for use
with vacuum box technology. Sr-Resin is available from Eichrom Technologies, Lisle, IL.
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quantitative or qualitative. MQOs serve as measurement performance criteria or
objectives of the analytical process.
3.7. Radiological Dispersal Device (RDD), i.e., a "dirty bomb." This is an unconventional
weapon constructed to distribute radioactive material(s) into the environment either by
incorporating them into a conventional bomb or by using sprays, canisters, or manual
dispersal.
3.8. Required Method Uncertainty (Z/MR). The required method uncertainty is a target value
for the individual measurement uncertainties and is an estimate of uncertainty (of
measurement) before the sample is actually measured. The required method uncertainty
is applicable below an AAL.
3.9. Relative Required Method Uncertainty (
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Total Radiostrontium ( Sr) in Water: Rapid Method for High-Activity Samples
4.1.2.2. Alternatively, Appendix B provides a numerical approach for the
isotopic determination 89Sr and 90Sr from two sequential counts of the
sample, one immediately following separation, and one after a delay to
allow for ingrowth of 90Y and decay of 89Sr. Note that the approach in
Appendix B must be validated prior to use.
910
4.1.3. High levels of Pb may interfere with low-level strontium analysis due to
ingrowth of short-lived 210Bi during chemical separations. If 210Pb is known to
be present in samples, minimizing the time between the final rinse and the
elution of strontium to less than 15 minutes will maintain levels of interfering
910 910
Bi to less than 0.1% of the Pb activity present. The presence or absence of
interfering 210Bi may be determined by recounting the sample test source to
verify the half-life of the nuclide present.
99R™, 99A 919
4.1.4. High levels of Th or its decay progeny Ra and Pb may interfere with
low-level strontium determinations due to ingrowth of short-lived decay
products during chemical separations. Monitoring count data for alpha activity
may provide indications of interferences. Minimizing the time between the final
rinse and the elution of strontium from the column to 5 minutes should maintain
919 90R
levels of interfering Pb and Tl to less than 2% of the parent nuclide
activity. The presence or absence of 212Pb may be determined by recounting the
sample test source to verify the half-life of the nuclide present.
4.1.5. Levels of radioactive cesium or cobalt in excess of approximately 103 times the
activity of strontium being measured may not be completely removed and may
interfere with final results.
4.2. Non-Radiological
4.2.1. Chemical yield results significantly greater than 100% may indicate the
presence of non-radioactive strontium native to the sample. If the quantity of
native strontium in the sample aliquant exceeds -5% of the expected strontium
carrier mass, chemical yield measurements will be affected and chemical yield
corrections lead to low result bias unless the native strontium is accounted for in
the yield calculations. When problematic levels of strontium are encountered,
the native strontium content of the sample can be determined by an independent
spectrometric measurement (such as inductively coupled plasma atomic
emission spectroscopy [ICP-AES] or atomic absorption spectroscopy [AAS],
etc). If the laboratory does not have access to instrumentation processing a split
of the sample without the addition of strontium carrier may be used to obtain an
estimate of the native strontium content of the sample.
4.2.2. Sr-Resin™ has a greater affinity for lead than for strontium. Lead will
quantitatively displace strontium from the column when the two are present in
combined amounts approaching or exceeding the capacity of the column. If the
combined quantity of lead and strontium carrier in the sample exceeds the
capacity of the column, decreased strontium yields will be observed. Decreasing
the sample size will help address samples with elevated levels of lead.
4.2.3. High levels of calcium, barium, magnesium, or potassium may compete with
strontium for uptake on the resin leading to low chemical yield. One should
consider that yield results will overestimate the true strontium yield and cause a
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Total Radiostrontium ( Sr) in Water: Rapid Method for High-Activity Samples
low result bias if these interfering matrix constituents are present as significant
contaminants in the final sample test source.
5. Safety
5.1. General
5.1.1. Refer to your safety manual for concerns of contamination control, personal
exposure monitoring and radiation dose monitoring.
5.1.2. Refer to the laboratory chemical hygiene plan for general chemical safety rules
5.2. Radiological
5.2.1. Hot Particles (DRPs)
5.2.1.1. Hot particles, also termed "discrete radioactive particles" (DRPs), will
be small, on the order of 1 mm or less. Typically, DRPs are not evenly
distributed in the media and their radiation emissions are not uniform
in all directions (anisotropic). Filtration using a 0.45-um or finer filter
will minimize the presence of these particles.
5.2.1.2. Care should be taken to provide suitable containment for filter media
used in the pretreatment of samples that may have DRPs, because the
particles become highly statically charged as they dry out and will
"jump" to other surfaces causing contamination.
5.2.1.3. Filter media should be individually surveyed for the presence of these
particles, and this information reported with the final sample results.
5.2.2. For samples with detectable activity concentrations of these radionuclides,
labware should be used only once due to potential for cross contamination.
5.3. Procedure-Specific Non-Radiological Hazards:
None noted.
6. Equipment and supplies
6.1. Analytical balance with 1 CT4-g readability or better.
6.2. Centrifuge able to accommodate 250-mL flasks and 50-mL centrifuge tubes.
6.3. Centrifuge flasks, 250 mL, disposable.
6.4. Centrifuge tubes, 50 mL, disposable.
6.5. Low-background gas flow proportional counter.
6.6. pH paper.
6.7. Stainless steel planchets or other sample mounts: ~2-inch diameter.
6.8. Vacuum box may be procured commercially, or constructed. Setup and use should be
consistent with manufacturer instructions or laboratory SOP.
6.9. Vacuum pump or laboratory vacuum system.
7. Reagents and Standards:
Note: All reagents are American Chemical Society (ACS) reagent grade or equivalent unless otherwise
specified.
Note: Unless otherwise indicated, all references to water should be understood to mean Type I Reagent
water (ASTM D1193).
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7.1. Barium carrier solution (10 mg Ba/mL, standardization not required): Dissolve 19 g
Ba(NO3)2 in water add 20 mL concentrated HNO3 and dilute to 1 L with water.
7.2. Ethanol, reagent 95% (C2HsOH), available commercially.
7.3. Nitric Acid, HNO3 (15.8M), concentrated, available commercially.
7.3.1. Nitric acid (8 M): Add 506 mL of concentrated HNO3 to 400 mL of water and
dilute to 1 L with water.
7.3.2. Nitric acid (3 M): Add 190 mL of concentrated HNO3 to 800 mL of water and
dilute to 1 L with water.
7.3.3. Nitric acid (0.1 M): Add 6.3 mL of concentrated HNO3 to 900 mL of water and
dilute to 1 L with water.
7.3.4. Nitric acid (0.05 M): Add 3.2 mL of concentrated HNO3 to 900 mL water.
Dilute to 1 L with water.
7.4. Nitric acid (3M)/oxalic acid solution (0.05 M): Add 190 mL of concentrated HNO3
(7.3) and 6.3 grams of oxalic acid dihydrate (C2H2O4-2H2O), to 800 mL of
demineralized water and dilute to 1 L with de-ionized water.
7.5. Sodium carbonate (2 M): Dissolve 212 g anhydrous Na2CO3 in 800 mL of water, then
dilute to 1 L with water.
7.6. Sodium hydroxide (12 M): Dissolve 480 g of sodium hydroxide (NaOH) in 500 mL of
water and dilute the solution to 1 L in water.
Caution: The dissolution of NaOH is strongly exothermic. Take caution to prevent boiling when
preparing this solution. Use of a magnetic stirrer is recommended. Allow to cool prior to use.
7.7. Sr-Resin™ columns,2 -0.7 g resin, small particle size (50-100 |j,m), in appropriately
sized column or pre-packed cartridge.
7.8. Strontium carrier solution, 5.00 mg/mL in 0.1-M HNO3, traceable to a national
standards body such as NIST or standardized at the laboratory by comparison to
independent standards.
7.8.1. Option 1: Dilute elemental strontium standard to a concentration of 5.00 mg/mL
(or mg/g) in 0.1-M HNO3.
7.8.2. Option 2: To 200 mL de-ionized water, add 6.3 mL HNO3 and approximately
12.07 g of strontium nitrate (Sr(NO3)2 dried to constant mass and the mass
being determined to at least 0.001 g). Dilute to 1000 mL with water. Calculate
the amount of strontium nitrate/mL actually present and verify per Step 7.8.3.
7.8.3. Prior to use, verify the strontium carrier solution concentration as by
transferring at least five 1.00-mL portions of the carrier to tared stainless steel
planchets. Evaporate to dryness on a hotplate or under a heat lamp using the
same technique as that used for samples. Cool in a desiccator and weigh as the
nitrate to the nearest 0.1 mg. The relative standard deviation for replicates
should be less than 5% and the average residue mass within 5% of the expected
value.
Available from Eichrom Technologies, Inc., Lisle IL.
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on
7.9. Sr standard solution (carrier free), traceable to a national standards body such as
NIST, in 0.5 M HNO3 solution.
8. Sample Collection, Preservation and Storage
8.1. Samples should be collected in 1-L plastic containers.
8.2. No sample preservation is required if sample analysis is initiated within 3 days of
sampling date/time.
8.3. If the sample is to be held for more than three days, HNOs shall be added until pH<2.
8.4. If the dissolved concentration of strontium is sought, the insoluble fraction must be
removed by filtration before preserving with acid.
9. Quality Control
9.1. Batch quality control results shall be evaluated and meet applicable Analytical Project
Specifications (APS) prior to release of unqualified data. In the absence of project-
defined APS or a project-specific quality assurance project plan (QAPP), the quality
control sample acceptance criteria defined in the laboratory quality manual and
procedures shall be used to determine acceptable performance for this method.
9.1.1. A laboratory control sample (LCS) shall be run with each batch of samples. The
concentration of the LCS should be at or near the action level or a level of
interest for the proj ect.
9.1.2. One method blank shall be run with each batch of samples. The laboratory
blank should consist of laboratory water.
9.1.3. One laboratory duplicate shall be run with each batch of samples. The
laboratory duplicate is prepared by removing an aliquant from the original
sample container.
9.1.4. A matrix spike sample may be included as a batch quality control sample if
there is concern that matrix interferences, such as the presence of elemental
strontium in the sample, may compromise chemical yield measurements, or
overall data quality.
9.2. This method is capable of achieving a MMR of 1.0 pCi/L at or below an action level of
8.0 pCi/L. This may be adjusted if the event-specific MQOs are different.
9.3. This method is capable of achieving a ^MR 13% above 8 pCi/L. This may be adjusted if
the event-specific MQOs are different.
9.4. This method is capable of achieving a required minimum detectable concentration
(MDC)of l.OpCi/L.
10. Calibration and Standardization
on
10.1. The effective detection efficiency for total radiostrontium (referenced to Sr) is
on on
calculated as the weighted sum of the Sr and Y efficiencies that reflects the relative
proportions of 90Y and 90Sr based on the 90Y ingrowth after 90Sr separation.
10.2. Set up, operate, and perform quality control for gas-flow proportional counters (GPC)
in accordance with the laboratory's quality manual and standard operating procedures,
and consistent with ASTM Standard Practice D7282, Sections 7-13 (see reference
16.5).
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on
10.3. See Appendix A for details on calibration/standardization of the GPC specific to Sr
and 90Y.
11. Procedure
11.1. For each sample in the batch, aliquant 0.5 L of raw or filtered water into a beaker.
Add concentrated HNCb with mixing to bring the solution to a pH less than 2.0.
Note: Smaller or larger aliquants may be used if elevated sample activity is present or as needed
to meet detection requirements or MQOs. Method validations must be conducted using a volume
equivalent in size to the sample size to be usedr
11.2. Add 1.00 mL (using a volumetric pipette) of 5 mg/mL strontium carrier and 0.5 mL
barium carrier. Record the volume of strontium carrier added and the associated
uncertainty of the mass of strontium added.
11.3. Place the beaker on a hotplate (for aliquants of 0.2 L a centrifuge cone in a hot water
bath may also be used) and heat the solution to near boiling with occasional stirring.
11.4. Add -0.4-0.5 mL (8 -10 drops) 0.1% phenolphthalein indicator solution per 200 mL
of sample. Add 12 M NaOH slowly with occasional stirring until a persistent pink
color is obtained.
Note: Additional phenolphthalein solution may be used if needed to provide a clear indication
that the pH is above ~8.3. A slight excess of NaOH may be added.
11.5. Add 30 mL of 2-M Na2CC>3 to the sample and digest for 15 minutes with occasional
stirring. Remove the sample from the hot plate and allow the solution to cool and the
precipitate to settle.
Note: Samples may be placed in an ice bath to expedite the cooling process.
Note: If greater than a 0.2-L aliquant is used, the supernatant solution is decanted or an
aspirator line used to remove as much supernatant solution as possible prior to transfer to a
centrifuge tube.
11.6. Transfer the sample to a centrifuge tube and centrifuge for 3 to 5 minutes at 1500-
2000 rpm. Discard supernatant solution.
11.7. Add 5 mL of 8-M HNOs to the centrifuge tube and vortex to dissolve the precipitate
containing Sr.
11.8. If there are no undissolved solids visible in the sample and the sample is not from an
RDD, or there is no reason to possibly suspect highly intractable material to be
present (e.g., insoluble ceramics), proceed with Step 11.11.
11.9. If the sample contains undissolved solids or may contain intractable material, cover
the tube to minimize evaporation of the solution and digest the solution on a hot water
bath for 30 minutes. Allow to cool.
11.10. If solids persist, remove by filtering solution through a glass fiber filter (1 um or
finer). The filter containing the solids should be analyzed separately for gross beta
activity (90Sr efficiency) to determine whether the AAL may be exceeded
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(screening ADLs apply). The solution containing soluble strontium is retained as
load solution for Step 11.13.
Note: See Section 12.3.2 for reporting results when liquid and solid fractions are analyzed
separately.
11.11. Set up a vacuum box for Sr-Resin™ columns or cartridges with minimum 10-15
mL reservoirs according the manufacturer's instructions or laboratory SOP. The
initial configuration should permit column effluents during the preconditioning,
sample loading and rinses (Steps 11.12- 11.16) to be discarded to waste.
11.12. Add 5 mL of 8-M HNOs to precondition the column. Adjust the vacuum as
necessary to maintain flow rates at < 3 mL/min. Discard preconditioning solution
effluent.
Note: Unless otherwise specified in the procedure, use a flow rate of ~ 1 mL/min for load and
strip solutions and ~ 3 mL/min for rinse solutions.
11.13. Decrease the vacuum to obtain flow rates of < 1 mL/min. Load the sample from
Step 11.8 or 11.10 into the column reservoir. When the solution reaches the top
surface of the resin proceed with the next step. Discard column effluent.
11.14. Adjust the vacuum as necessary to maintain flow rates at < 3 mL/min. Rinse
centrifuge tube with three successive 3 mL portions of 8-M HNCh adding the next
one after the previous one reaches the top of the resin column. Discard column
effluent.
11.15. If plutonium, neptunium, or radioisotopes of ruthenium or cerium may be present in
the sample, add 10 mL 3-M HNOs - 0.05-M oxalic acid solution to each column.
Allow the solution to completely pass through the column prior to proceeding.
Adjust the vacuum as necessary to maintain flow rates at < 3 mL/min. Discard
column effluent.
11.16. Remove residual nitric/oxalic acid solution with two 3 mL rinses of 8-M HNCh,
allowing each rinse solution to drain before adding the next one. Adjust the vacuum
as necessary to maintain flow rates at < 3 mL/min. Record time and date of the end
of last rinse to the nearest 15 minutes as t\, "time of strontium separation." Discard
column effluent.
11.17. Place clean 50 mL centrifuge tubes beneath the columns to catch the strontium
eluate before proceeding to the next step.
11.18. Decrease the vacuum as necessary to maintain flow rates at< 1 mL/min. Elute
strontium from the columns by adding 10 mL of 0.05-M HNOs.
11.19. Preparation of the STS and determination of chemical yield
11.19.1. Clean and label a stainless steel planchet for each STS.
11.19.2. Weigh and record the tare mass of each planchet to the nearest 0.1 mg.
11.19.3. Transfer the strontium eluate from Step 11.18 to the planchet and take to
dryness on a hotplate or under a heat lamp to produce a uniformly distributed
residue across the bottom of the planchet.
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11.19.4. When dry, place the sample in an oven at 105-110 °C until shortly before
sample test sources are ready for weighing. At that point, remove the STS
from the oven and allow it to cool in a desiccator before weighing.
11.19.5. Weigh and record the gross mass of each planchet to the nearest 0.1 mg.
Note: If the laboratory cannot operationally ensure that the precipitate has been
dried to constant mass, the mass stability of the precipitate should be demonstrated
by reheating the precipitate in an oven at 105-110 °C and reweighing. Since sample
self-attenuation is not a significant factor in the detection efficiency, the sample may
be counted prior to completion of this step if desired.
11.19.6. Calculate the chemical yield as presented in Section 12 of this method.
11.20. Counting the Sample Test Source
11.20.1. On a calibrated gas-flow proportional detector that has passed all required
daily performance and background checks, count the STS for a period as
needed to satisfy MQOs.
OQ
11.20.1.1. If the presence of Sr cannot be excluded, and total
radiostrontium is being determined as a screen for the presence
of 89Sr or 90Sr, count the STS as soon as practicable after
on
preparation to minimize the ingrowth of Y into the STS.
11.20.1.2. If the presence of 89Sr can be excluded, total radiostrontium
QO
will provide isotopic Sr results and the STS may be counted
at any time after preparation.
11.20.2. Calculate the total radiostrontium (90Sr) sample results using calculations
presented in Section 12.
12. Data Analysis and Calculations
12.1. Calculation of Total Radiostrontium
12.1.1. When a sample is analyzed for total radiostrontium (equivalent 90Sr), the
effective efficiency is calculated as follows:
Sr ~ ° Sr90 ' V1 *" ) ^ ° Y90 \ )
where
£iotai Sr = effective detection efficiency for total radiostrontium
£sr9o = final 90Sr detection efficiency
£Y9o = final 90Y detection efficiency
AY90 = decay constant for 90Y, 3.008x 10~6 s"1
t\ = date and time of the Sr/Y separation
h = date and time of the midpoint of the count
Note: The elapsed time between the sample count and the reference date must be
calculated using the same time units as the decay constant.
12.1.2. The standard uncertainty of the effective efficiency is calculated as
follows:
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e^9°(^2^^^ (2)
where
Note: The terms u(sSr90, £y9o) and r(sSr90, £Y90) are derived during calibrations as shown in
Appendix A, Section 4.
12.1.3. The total radiostrontium activity concentration (^Ciotai sr) equivalent to
90Sr is calculated as follows:
where
DF = e-***>&-U (4)
and where
R& = beta gross count rate for the sample (cpm)
Rb = beta background count rate (cpm)
fiiotai sr = effective efficiency of the detector for total strontium
referenced to 90Sr
7 = fractional chemical yield for strontium
V = volume of the sample aliquant (L)
DF = correction factor for decay of the sample from its
reference date until the midpoint of the total strontium
count
Asr90 = decay constant for 90Sr, 7.642x 1(T10 s"1
to = reference date and time for the sample
t\ = date and time of the Sr/Y separation
Note: The elapsed time between the sample count and the reference date must be
calculated using the same time units as the decay constant
12. 1 .4. The standard counting uncertainty of the total radiostrontium activity
concentration, wcc04Cxotai sr) is calculated as follows:
u (AC \-
11 cC V1*- Total Sr/ ~~
where:
2.22x£Ttls xYxVxDF
i oiai or
4 = Duration of the sample count (min)
tb = Duration of the background subtraction count (min)
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12. 1.5. The combined standard uncertainty (CSU) for the total radiostrontium
activity concentration, uc(ACi0^\ sr), is calculated as follows:
I Af- ^ A^
tal Sr = cc (ACTM Sr ) + ACTotal Sr
'Total Sr
u\Y) u\V}
Y2 y2
(6)
where:
u(Y) = standard uncertainty of fractional chemical yield for strontium
w(V) = standard uncertainty of the volume of the sample aliquant (L)
S =
12.1.6. If the critical level concentration (Sc) or the minimum detectable
concentration (MDC) are requested (at an error rate of 5%), they can be
calculated using the following equations:3
t Y999Y.P
is x z.zz x6TotalSr
(7)
When the Type I decision error rate, a, equals 0.05, z\-a = 1.645, and the constant, d, from
the Stapleton approximation is set to 0.4, the expression above becomes:
0.4 x I — -I + 0.677 x
^- + 1.645 x \(Rbtb +0.4)x
*b J V *b
tsx2.22xsTotalSixYxVxDF
(7a)
MDC =
lRbtsx h+-
tsx2.22xsTotalSrxYxVxDF
(8)
3 The formulations for the critical level and minimum detectable concentrations are as recommended in MARLAP
Section 20A.2.2, Equations 20.54 and Equation 20.74, respectively. For methods with very low numbers of counts,
these expressions provide better estimates than do the traditional formulas for the critical level and MDC assuming
that the observed variance of the background conforms to Poisson statistics. Consult MARLAP when background
variance may exceed that predicted by the Poisson model or when other decision error rates may apply.
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When the Type I decision error rate, a, equals 0.05, zi_a = 1.645, and the Type II decision
error rate, ft equals 0.05, zi_p = 1.645, the expression above becomes:
MDC =
2.71x 1 + -- +3.29x IRt x 1 + --
I V
tsx2.22xsTotalSrxYxVxDF
(8a)
12.2. Chemical Yield for Strontium
12.2.1. Calculate the chemical yield for strontium using the gravimetric data
collected in Step 11.18:
OTA(N03)2
c,V,+cnV
where:
Y = strontium yield, expressed as a fraction
m$ = mass of Sr(NO3)2 recovered from the sample (g)
-^srfNo ) = gravimetric factor for strontium weighed as the nitrate,
414.0 mg Sr/g Sr(NO3)2
cc = Sr mass concentration in the strontium carrier solution
(mg/mL)
Fc = volume of strontium carrier added to the sample (mL)
cn = Sr mass concentration native to the sample - if
determined (mg/L)
V = volume of sample aliquant (L)
12.2.2. Calculate the standard uncertainty of the yield as follows:
7 ,( )+ .
"1 I 1 \ S x / T7" T 7"\ 2. ^ '
V (ccVc+cnV}
where
u(-} = standard uncertainty of the quantity in parentheses,
Mr(0 = relative standard uncertainty of the quantity in parentheses.
12.3. Results Reporting
12.3.1. Unless otherwise specified in the APS, the following items should be
reported for each result:
12.3.1.1. Result for total radiostrontium (Step 12.1.3) in scientific
notation ± 1 combined standard uncertainty.
12.3.1.2. Volume of sample aliquant and any dilutions used.
12.3.1.3. Yield of tracer and its uncertainty.
12.3.1.4. Case narrative
12.3.1.5. The APS may specify reporting requirements for samples
originating from an RDD or other event where intractable
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material (e.g., strontium titanate) may be present. If specific
guidance is not provided, but intractable materials are likely
present in samples, the results for soluble strontium (from the
aqueous phase) should be reported per Step 12.3.2.
12.3.2. If solid material was filtered from the solution and analyzed separately, the
gross beta results from the direct count of filtered solids should be
calculated as "gross beta (90Sr)" or "gross beta equivalent 90Sr" and
reported separately in terms of pCi/L of the original volume of sample.
For example:
90Sr for Sample 12-1-99:
Filtrate result: (1.28 ± 0.15) x K^pCi/L
Gross beta (90Sr) filtered residue result: (2.50 ± 0.30) x 10° pCi/L
13. Method Performance
13.1. Results of method validation performance are to be archived and available for
reporting purposes.
13.2. Expected turnaround time per sample or per batch (See Figure 17.4 for typical
processing times (assumes samples are not from RDD).
13.2.1. Preparation and chemical separations for a batch of 20 samples can be
performed by using two vacuum box systems (12 ports each).
simultaneously, assuming 24 detectors are available. For an analysis of a
500 mL sample aliquant, sample preparation and digestion should take
-3-4 h.
13.2.2. Purification and separation of the strontium fraction using cartridges and
vacuum box system should take -0.5-1.2 h.
13.2.3. Sample test source preparation takes -0.75 - 1.5 h.
13.2.4. A 100-minute counting time is sufficient to meet the MQO listed in Step
9.2, assuming 0.5 L aliquant, a background of 1 cpm, detector efficiency
of 0.3-0.4, and radiochemical yield of at least 0.5.
13.3. Total radiostrontium (90Sr) data reduction should be achievable between 6 and 9
hours after the beginning of the analysis.
13.4. The sample may be recounted following a delay of 1-21 days to verify the
radiochemical purity of 90Sr. If the source contains pure 90Sr, the total
radiostrontium activity calculated from the two counts should agree within the
uncertainty of the measurements. Minimizing the time between the chemical
separation of Sr and the initial count, longer count times, and increasing the delay
between the two counts, will minimize the overall uncertainty of the data and
provide more sensitive and reliable measures of the radiochemical purity of the
STS.
Note: The 89Sr and 90Sr may be determined from two consecutive counts of the source -
calculations are presented in Appendix B. This approach must be validated prior to use.
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14. Pollution Prevention
14.1. The use of Sr-Resin™ reduces the amount of acids and hazardous metals that would
otherwise be needed to co-precipitate and purify the sample and prepare the final
counting form.
15. Waste Management
15.1. Nitric acid and hydrochloric acid wastes should be neutralized before disposal and
then disposed in accordance with prevailing laboratory, local, state and federal
requirements.
15.2. Initial column effluents contain mg/mL levels of barium and should be disposed in
accordance with prevailing laboratory, local, state and federal requirements.
15.3. Final precipitated materials may contain radiostrontium and should be treated as
radioactive waste and disposed in accordance with the restrictions provided in the
facility's radioactive materials license and any prevailing local restrictions.
15.4. Used resins and columns should be considered radioactive waste and disposed of in
accordance with restriction provided in the facility's radioactive materials license
and any prevailing local restrictions.
16. References
16.1. SRW04-11, "Strontium 89, 90 in Water," Eichrom Technologies, Inc., Lisle,
Illinois (February 2003).
16.2. "Rapid Column Extraction Method for Actinides and 89/90Sr in Water Samples,"
S.L. Maxwell III. Journal of Radioanalytical and Nuclear Chemistry 267(3): 537-
543 (Mar 2006).
16.3. U.S. Environmental Protection Agency (EPA). 2009. Method Validation Guide for
Radiological Laboratories Participating in Incident Response Activities. Revision
0. Office of Air and Radiation, Washington, DC. EPA 402-R-09-006, June.
Available at: www.epa.gov/narel/incident guides.html and
www.epa.gov/erln/radiation.html.
16.4. Multi-Agency Radiological Laboratory Analytical Protocols Manual (MARLAP).
2004. EPA 402-B-1304 04-001A, July. Volume I, Chapters 6, 7, 20, Glossary;
Volume II and Volume III, Appendix G. Available at: www.epa.gov/radiation/
marlap/index.html.
16.5. ASTM D7282 "Standard Practice for Set-Up, Calibration, and Quality Control of
Instruments Used for Radioactivity Measurements," ASTM Book of Standards
11.02, current version, ASTM International, West Conshohocken, PA.
16.6. SR-04, "Radiochemical Determination of Radiostrontium in Water, Sea Water, and
Other Aqueous Media," Eastern Environmental Radiation Facility (EERF)
Radiochemistry Procedures Manual, Montgomery, AL, EPA 520/5-84-006 (August
1984).
16.7. ASTM Dl 193, "Standard Specification for Reagent Water," ASTM Book of
Standards 11.02, current version, ASTM International, West Conshohocken, PA
16.8. Nuclear data from NUDAT 2.3 and the National Nuclear Data Center at
Brookhaven National Laboratory; available at www.nndc.bnl.gov/nudat2/indx
dec.jsp, database version of 6/30/2009.
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17. Tables, Diagrams, Flow Charts and Validation Data
17.1. Validation Data
This section intentionally left blank.
17.2. Nuclide Decay and Radiation Data
Table 17.1. Decay and Radiation Data
Nuclide
90Sr
90y
89Sr
Half-life
(days)
1.052E+04
2.6667
50.53
X
or1)
7.642xlO"10
3.005xlO"6
1.587X10'7
Abundance
1.00
1.00
1.00
Pmax
(MeV)
0.546 MeV
2.280 MeV
1.495 MeV
A*
(MeV)
0.196 MeV
0.934 MeV
0.585 MeV
17.3. Ingrowth and Decay Curves and Factors
In-Growth Curve for 90Y in 90Sr
100
200 300 400 500
Time Elapsed After Sr-90 Separation (h)
^^^Y-30 Sr-90 - - - Beta Adivtty
600
700
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Table 17.2. Total Beta Activity Ingrowth Factors for 90Y in 90Sr
Ingrowth time elapsed (hours)
Factor
Ingrowth time elapsed (hours)
Factor
0.25
0.003
144
0.790
2
0.021
192
0.875
4
0.042
240
0.926
12
0.122
320
0.969
24
0.229
400
0.987
48
0.405
480
0.994
72
0.541
560
0.998
96
0.646
640
0.999
Factor = (90 Y activity/90Sr activity at zero hours of ingrowth)
1
1
5
c
Q.5 ~
o
S3
89 £
Decay Curve for Sr
100 200 300 400
Time Elapsed since collection (h)
— Sr-89 Activity
500
600
700
89r
Table 17.3. Decay Factors for oySr
Decay time elapsed (hours)
Factor
Decay time elapsed (hours)
Factor
0.25
1.000
144
0.921
2
0.999
192
0.896
4
0.998
240
0.872
12
0.993
320
0.833
24
0.986
400
0.796
48
0.973
480
0.760
72
0.960
560
0.726
96
0.947
640
0.694
Factor = ( Sr activity/ Sr activity at zero hours of ingrowth)
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17.4. Decay Schemes for 89Sr and 90Sr
89Sr and 90Sr Decay Scheme
= l.l5WleV
,= 50.53 d
p = 0.55 MeV
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17.5. Process Flow with Typical Processing Times (assumes no filtration necessary)
Elapsed
Time
Hrs
1.0
3.0
3.5
4.0
4.5
5.5
6.0
7.0
27-90
Aliquant sample, add HN03 to pH <2; Add Sr
and Ba carriers (11.1-11.2)
Add Na2C03to precipitate; Digest and allow to
cool; Settle/centrifuge (11.5-11.6)
Heat sample (11.3)
Add indicator and adjust to phenolphthalein
endpoint with NaOH (11.4)
Cover and digest
sample for 30
minutes
Continue with 11.10
(11.8)
.,-""Ondissolved'"\
residue \ 'es
present?
(11.10) /
Load sample onto prepared
column at £1 mUmin.
(11.13)
Prepare and
precondition column
with 5 ml 8M HN03
(11.11-11.12)
Analyze filter for
gross beta.
Evaluate results
against MSr
Screening ADLs.
(11.10)
Sr Resin
Column
Adjust flow to £3 rriL/min. Rinse
centrifuge tube with three 3-mL rinses of
8 M HN03 adding each to column (11.14)
If Ce, Ru, Pu.or Np may be present, strip
with 10 rriLHN03/oxalic reagent (11.15)
Remove residual HN03/oxalic acid with
two Stvl HN03 rinses. Record t, (11.16)
Replace tube to retain eluate. Adjust flow
to S1 mb'min. Elute Sr with two 5 ml
portions of0.05 M HI\IQ3 (11.17-11.18)
Retain Sr eluate (11.17-11.18)
Discard precondition (11.12),
load (11.13) and strip and rinse
(11.14-11.16) effluents
Quantitatively transfer and evaporate Sr eluate onto clean, tared planchet (11.19.1-11.19.4)
Dry to constant mass and weigh to determine chemical yield (11.19.5-11.19.6)
Beta Count with Gas Flow Proportional Counter to determine Total Sr activity
(11.20.1-11.20.2)
Recount to verify forMSr if required by APS
(11.20.1-11.20.2)
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Appendix A
Method and Calculations for Detector Calibration
on
Al.The effective detection efficiency for total radiostrontium (referenced to Sr) is calculated as
the weighted sum of the 90Sr and 90Y efficiencies that reflects the relative proportions of 90Y
on on
and Sr based on the Y ingrowth after strontium separation.
Note: While 89Sr efficiency calibration is not needed unless 89Sr analysis will be performed, instructions
for preparation are provided to support the two count approach should this option be desired.
ALL Due to the low mass of carrier used for this method, self-absorption effects may be
assumed to be constant. Calibrate each detector used to count samples according to
ASTM Standard Practice D7282, Section 16, "Single Point Efficiency or Constant
Test Mass for a Specific Radionuclide" and the instructions below.
Al .2. Prepare a blank and at least three working calibration sources (WCS) for 90Sr and
90Y, and 89Sr (if needed) as follows:
Al .2.1. The 90Sr and 89Sr radioactive standard solutions used to prepare WCSs
shall be traceable to a national standards body such as NIST and shall
originate from a standards supplier (or lot) different from standards used
for calibration verification and batch quality controls. The standards
should be diluted in nitric acid.
Al.2.2. The planchets used for the sources shall be of the same size, materials and
type as those used for the analysis of STSs.
Al.2.3. Preparation of 89Sr WCSs (if needed): 89Sr standard solution (in 0.5-M
HNOs) is evaporated to dryness in a stainless steel planchet as follows:
OQ
Al.2.3.1. For each Sr WCS to be prepared, and for the associated
blank, add a strontium carrier to 10 mL of 0.05-M HNOs in a
disposable 50-mL centrifuge tube. The amount of carrier
should be adjusted to approximate the amount expected to be
recovered from routine samples.
Note: If the average recovery has not been determined, the laboratory
may assume 85% chemical yield for determining the amount of carrier
to use in Step 1.2.3.1.
Note: If the 89Sr standard contains residual chloride, it will attack the
surface of the planchet and compromise the quality of the calibration
standard. In such cases, convert the aliquant of standard solution to a
nitrate system by adding 1 mL concentrated HNOs and taking to
dryness 2 times prior to quantitatively transferring the solution to the
planchet.
OQ
Al.2.3.2. For each WCS, add a precisely known amount of traceable Sr
solution to a 50-mL centrifuge tube. Sufficient activity must be
present at the point of the count to permit accumulation of
greater than 10,000 net counts in a counting period deemed to
be reasonable by the laboratory. The minimum activity used,
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however, should produce WCS count rates at least 20 times the
background signal but not greater than 5000 cps.
Al .2.3.3. Mix the solution and quantitatively transfer each WCS and the
blank to respective clean stainless steel counting planchets
using three rinses of 0.05-M HNCb.
Al .2.3.4. Evaporate to dryness using the same techniques used for
sample test sources.
on
Al.2.3.5. For each detector to be calibrated, count three Sr WCSs for
sufficient time to accumulate at least 10,000 net counts.
Al .3. Preparation of 90Sr and 90Y WCSs: Separate WCSs for 90Sr and 90Y are prepared by
chemically separating 90Y from a standard solution of 90Sr.
Al .3.1. For each 90Sr WCS to be prepared, and for the associated blank, add 1 mL of
5 mg/mL strontium carrier to a disposable 50-mL centrifuge tube. The
amount of carrier added should correspond to that expected to be recovered
from a routine sample.
Note: If the average recovery has not been determined, the laboratory may assume
85% chemical yield for determining the amount of carrier to use for Step 1.3.1.
Al.3.2. For each 90Sr WCS, add a precisely known amount of traceable 90Sr solution
to a 50-mL centrifuge tube. Sufficient activity should be present at the point
of the count to permit accumulation of greater than 10,000 90Sr and 10,000
90Y net counts in the respective sources in a counting period deemed to be
reasonable by the laboratory. The minimum activity used, however should
produce WCS count rates at least 20 times the background signal but not
greater than 5000 cps.
Al .3.3. Set up one Sr Resin column for each 90Sr WCS and for the associated blank.
Condition each column with 5 mL of 3-M FDSTCb. Column effluents are
discarded to waste.
on
Al.3.4. Place a clean centrifuge tube under each column to catch all combined Y
effluents.
Note: Unless otherwise specified in the procedure, use a flow rate of ~ 1 mL/min for
load and strip solutions and ~ 3 mL/min for rinse solutions.
QO
Al.3.5. Load the Sr solution onto the column. The load solution effluent
on
containing Y is retained.
Al .3.6. Rinse the centrifuge tube with three successive 2-mL portions of 3-M FINOs
adding each of the rinses to the column after the previous rinse has reached
the upper surface of the resin. These effluents also contain 90Y and are
retained.
Al .3.7. Rinse the column with 5 mL of 3 M FENCb and retain the column effluents
containing 90Y. Record the date and time that the final rinse solution leaves
the column to the nearest 5 minutes as t\, "Time of 90Y Separation." Remove
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on
the centrifuge tube that has the combined Y effluents. Place a clean tube
under the column to catch the strontium eluate in subsequent steps.
NOTE: From this point, 90Sr must be eluted, and the 90Sr WCS must be prepared and
counted as expeditiously as possible to minimize 90Y ingrowth and necessary
corrections to the efficiency. Counting of the 90Sr WCS should be completed, if
possible, within 3-5 hours but no longer than 10 hours from the time of 90Y
separation. If processing or counting capacity is limited, concentrate resources on 90Sr
WCS and counting first. The 90Y WCS are not compromised by ingrowth but must
only be counted promptly enough to minimize decay and optimize counting statistics.
Al.3.8. Strip strontium from each column by adding 10 mL of 0.05-M HNOs to
on
each column, catching the effluents containing Sr in the centrifuge tube.
Al .3.9. Quantitatively transfer 90Sr and 90Y fractions to respective tared planchets
using three portions of 0.05-M
Al.3.10. Evaporate to dryness using the same techniques used for sample test
sources.
Note: Gravimetric measurements may be performed following the counting to
minimize elapsed time between separation and counting.
Al .4. Weigh the 90Sr and 90Y WCS sources and calculate the net residue mass.
Al .4.1. The net mass of the strontium nitrate precipitate shall indicate near
quantitative yield of strontium of 95-103%. If strontium yield falls outside
this range, determine and address the cause for the losses and repeat the
on
process. The known activity of Sr in the standard is corrected for losses
based on the measured chemical yields of the strontium carrier.
Note that no correction shall be applied for values greater than 100% because this will
produce a negative bias in the calibrated efficiency.
on
Al .4.2. The net residue mass of the Y should be equivalent to that of the
associated blank (i.e., -0.0 mg). Higher residue mass may indicate the
breakthrough of strontium and will result in high bias in the 90Y efficiency.
If blank corrected net residue mass exceeds 3% of the strontium carrier
added, determine and address the cause for the elevated mass and repeat the
process.
Al .4.3. Count three 90Sr WCS on each detector to be calibrated, for sufficient time
to accumulate at least 10,000 net counts.
Al .4.4. Count three 90Y WCS on each detector to be calibrated, for sufficient time to
accumulate at least 10,000 net counts.
Al.4.5. Count the associated blanks as a gross contamination check on the process.
If indications of contamination are noted, take appropriate corrective actions
to minimize spread and prevent cross-contamination of other samples in the
laboratory.
Al .5. Verify the calibration of each detector according to ASTM Standard Practice D7282,
Section 16, and the laboratory quality manual and standard operating procedures.
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Al .6. Calculations and data reduction for 90Sr and 90Y calibrations and calibration
verifications are presented in Sections A2, A3, and A4. Calculations for total
radiostrontium are in Section 12.
A2. Calculation of Detection Efficiency for 90Sr
A2. 1 . Calculate the following decay and ingrowth factors for each WCS:
DFS = e-*««>&-V (Al)
/FY90 =l-e^™('2"'l) (A2)
where
on
DFS = decay factor for decay of the Sr standard from its reference date
until the 90Sr/90Y separation
= ingrowth factor for ingrowth of 90Y after the 90Sr/90Y separation
= decay constant for 90Sr, 7.642x 1(T10 s"1
AY90 = decay constant for 90 Y, 3 .005 x 1 (T6 s"1
on
to = reference date and time for the Sr standard
t\ = date and time of the Sr/Y separation
ti = date and time of the midpoint of the 90Sr count
Note: The elapsed time between the sample count and the reference date must be calculated
using the same time units as the decay constant
A2.2. Calculate the 90Sr detection efficiency for each WCS:
K — K R
p - _ s-> b __ 777 XP - _ ll __ 7/7 XP (A3">
GSr90,i ~ ..-, T7 r^r il Y90,i CY90 . ^, T7 ,-. ^ ^ Y90,i A CY90 \f^J )
ACSI90 std x Fs>1. x DFSJ ACSI90 std x Fs>1. x DFSJ
where
£sr9o,i = 9°Sr detection efficiency for the f WCS
_ Qj-\
£"Y90 = average Y detection efficiency (from Step A3. 2)
R^t = beta gross count rate for the f WCS(incpm)
Rb = background count rate, in cpm
Rn i = beta net count rate for the f WCS (cpm)
' Qj-\
ACsr90sti = activity concentration of the Sr standard solution on its
reference date (cpm/mL or cpm/g)
FS;; = amount (volume or mass) of the standard solution added to the
/thwcs
A2.3. Average the efficiencies determined in Step A2.2 for all the WCSs to obtain the final
detection efficiency for 90Sr.
where
= Sr detection efficiency determined for the /' WCS in A2. 2,
n = number of WCSs prepared and counted.
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90 c
A2.4. Calculate the standard uncertainty of the average Sr detection efficiency as follows
\U (£Y9o) £Y90Wr (•<4(-Sr90std)/-"V Y9° + SSr90Ur V^^Sr90std
(A5)
where
1 n QD
= — y,/FY90),. = average value of Y ingrowth factors
and
w(-) = standard uncertainty of the value in parentheses,
wr(-) = relative standard uncertainty of the value in parentheses.
90,
(A6)
A3.Detect!on Efficiency for Y
90
A3.1. Calculate the Y detection efficiency, eygo,*, for each WCS,
where
and
Rn,i
DFS
t\
90
(A7)
(A8)
Y detection efficiency determined for the WCS
= beta gross count rate for the /'th WCS (cpm)
= background count rate, in cpm
= beta net count rate for the f WCS (cpm)
on
std = activity concentration of the Sr standard solution on its reference
date (dpm/mL or dpm/g)
= amount of the standard solution added to the /'* WCS (mL or g)
= combined correction factor for decay of the 90Sr standard in the f
WCS from its reference date until 90Y separation, and for the decay
of 90Y from its separation until the midpoint of the count
90
10 "1
= decay constant for Sr, 7.642x 1(T s
= decay constant for 90Y, 3.005x 10"6 s"1
QO
= reference date and time for the Sr standard
= date and time of the 90Y separation
on
= date and time at the midpoint of the Y count
Note: The elapsed time between the sample count and the reference date must be calculated using the
same time units as the decay constant
A3.2. Average the efficiencies determined in Step A3.1 to obtain the final detection
efficiency for 90Y.
'Y90
(A9)
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where
= 9°Y detection efficiency determined for the /'* WCS in Step A3 . 1
n = number of WCS prepared and counted
A3. 3. The combined standard uncertainty of the average efficiency for 90Y including
uncertainty associated with the preparation of the calibration standards is calculated
as follows:
(A10)
where
u(-) = standard uncertainty of the value in parentheses,
Mr(-) = relative standard uncertainty of the value in parentheses.
NOTE: The uncertainty of the net count rate, uRn^ includes the uncertainty of the background
or
u2 (R^) = U2(RS) + u2(R6) = (Rs/ts) + (R6/tfi)
A4. Calculate the covariance and correlation coefficient for the 90Sr efficiency and the 90Y
efficiency:
«(eSr90 = gY90 ) = SSr90SY90«r2 (^CSr90 std ) ~ (« ' («Y90 ) ~ ^90Ul (ACSt90 std ))^ Y90 (All)
and
where
u(-,-) = estimated covariance of the two quantities in parentheses,
r(-, •) = estimated correlation coefficient of the two quantities in
parentheses,
u(-) = standard uncertainty of the quantity in parentheses,
ur(-) = relative standard uncertainty of the quantity in parentheses.
OQ
A5 .Detection Efficiency for Sr (if needed for Appendix B Calculations)
A5. 1 . Calculate the detection efficiency, esr89,*, for each WCS as follows:
gM9,= ^"^b - = - ^ - (A13)
' AC^V^DF^ AC^V^DF^
where
DFSI = e-*»- (A14)
and
= 89Sr detection efficiency for the f WCS
= beta gross count rate for the/'* WCS (cpm)
= background count rate, in cpm
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Total Radiostrontium ( Sr) in Water: Rapid Method for High-Activity Samples
QQ
std = activity concentration of the Sr standard solution on the reference
amount (volume or mass) of the standard solution added to the/'*
date (dpm/mL or dpm/g)
= amount (volume
WCS (mL or g)
= correction factor for decay of the 89Sr standard for the f WCS
from its reference date until the midpoint of the sample count
decay constant for 89Sr, 1.372x 10~2 d"1
OQ
to = reference date and time for the Sr standard
OQ
t\ = date and time at the midpoint of the Sr count
A5.1.1. Average the efficiencies determined in Step A5.1 to obtain the final detection
efficiency for 89Sr.
1^
-
where
£sr89,* = 89Sr detection efficiency determined for the /'* WCS in Step A5. 1,
n = number of WCSs prepared and counted.
___ OQ
A5. 1 .2. The combined standard uncertainty of the average efficiency for Sr including
uncertainty associated with the preparation of the calibration standards is
calculated as follows:
where
M(-) = standard uncertainty of the value in parentheses,
wr(0 = relative standard uncertainty of the value in parentheses.
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Total Radiostrontium ( Sr) in Water: Rapid Method for High-Activity Samples
Appendix B:
JiQ OH
Calculations for Isotopic Sr and Sr Results
QQ Qf\
A numerical approach for determining Sr and Sr activity from a single sample is performed
by a number of laboratories. This presentation, however, allows a more rigorous evaluation of
uncertainties than commonly employed. Lacking this treatment, many labs have found that the
traditional approach (evaluating counting uncertainty for a single count only) has led to
overestimation of the quality of results, and to poor decisions regarding the presence or absence
of low activities of one radioisotope of strontium in the presence of elevated activities of the
second.
___ OQ Qf\
These calculations may be valuable to laboratories who wish to determine isotopic Sr and Sr
in a large number of samples with a minimum of additional effort beyond the initial preparation
and counting of total radiostrontium. Specifically, it involves performing a second count of the
same radiostrontium sample test source (STS) and mathematically resolving the activity of the
two isotopes. Although the STS may be recounted as soon as 1-2 days after the initial count,
on
resolution is optimized if the two counts span as large a range of the Y ingrowth as practicable.
The time elapsed between the chemical separation and the first count should be minimized, while
the second count should optimally proceed as 90Y approaches secular equilibrium with 90Sr but
before significant decay of 89Sr has occurred, for example, after 3-5 half-lives of 90Y have
elapsed (1-2 weeks).
This section may not be employed without complete validation of the approach by the
laboratory, including testing with samples containing ratios of 90Sr relative to 89Sr varying from
on °>Q
pure Sr to pure Sr.
Bl.The equations in this section are used to calculate the 90Sr and 89Sr activity of a sample from
data generated from two successive counts of the same radiostrontium sample test source.
B 1 . 1 . For each of the two counting measurements (/' = 1 , 2), calculate the following decay
and ingrowth factors:
(Bl)
(B2)
77 _ ~Si9oiep~o M _ ~
/Y90,z ~ C
where:
OQ
= decay factor for decay of Sr from the collection date to the
midpoint of the f count of the STS
= decay factor for decay of 90Sr from the collection date to the
midpoint of the /'th count of the STS
QO
= combined decay and ingrowth factor for decay of Sr from the
Qj-\
collection date to the Sr/Y separation and ingrowth of Y from the
separation to the midpoint of the /'th count of the STS
= decay constant for 89Sr = 1 .58?x 1(T7 s"1
= decay constant for 90Sr = 7.642x 1(T10 s"1
= collection date and time for the sample
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4ep = date and time of the Sr/Y separation
ti = date and time of the midpoint of the /'th count of the STS
Note: The elapsed time between the sample count and the reference date must be calculated
using the same time units as the decay constant
B 1 .2. For / = 1,2, use the results from Section A5 . 1 in Appendix A to calculate the
following sensitivity factors:
«,- = £tfW%89,,- (B4)
" ~ -
where
at = sensitivity of the count rate in the /'* measurement to 89Sr activity,
bj = sensitivity of the count rate in the /'* measurement to 90Sr activity.
= 9°Y efficiency of the detector for the f count of the STS,
= 9°Sr efficiency of the detector for the f count of the STS.
B1.3. Calculate the standard uncertainties of the sensitivity factors using the equations:
j «(%89,- ) (B6)
90,,' U 2 (£Y90,,- ) + 2DFSr90,lFJ90,l U (SSr90,, , SV90,, ) (B7)
where the estimated covariance of the 90Sr and 90Y efficiencies is calculated as
follows:
M(«Si90,,-.«Y90,,-) = 'I(«Si90,,-^Y90,-)"(«Si90,,-)"(«Y90,-) (B8)
and where the estimated correlation coefficient r(eSr9o,*, £Y9o,0 was determined during
the calibration.
B1.4. Calculate the covariances u(a\,ci2) and u(b\,b2) as follows:
u(al)u(a2 ), if only one detector is used
u(al:,a2) = \ 2 (B9)
1 2 ala2uI (ACSlWsid)., it two detectors are used
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where
5190,2-^^-90,1 )U(£Si90,l •> ^¥90,1 /
DFsr9o,2 u ' (£5r9o,i ) + ^Y9o,i ^Y9o,2 u ' (
Y9o,i
^(ACSl90std),
X using only one detector (B 1 0)
using two detectors
= activity concentration of the Sr standard used for calibration
on
Csr90 std = activity concentration of the Sr standard used for calibration
Mr(-) = relative standard uncertainty of the quantity in parentheses
B1.5. For / = 1,2, calculate the net beta count rates, Rn^, and their standard uncertainties:
(B12)
where:
•th
= net beta count rate for the / count of the STS (cpm)
'*
= beta gross count rate for the/' count of the STS (cpm)
= beta background count rate for the count of the STS (cpm)
'
= sample count time for the /' count of the STS (min)
'th
= background count time for the /'t count of the STS (min)
90
B1.6. Using the values calculated in A5.1 - A5.5, calculate the Sr and Sr activity
concentrations:
AC=
AC=
SI90
Sr9°
— — — -IT- JT -TT-
2.22xXxVxY
2.22xXxVxY
where:
= alb2-a2bl
l2-2l
(B13)
\ /
(B14)
^ }
(B15)
and where:
2.22 = conversion factor from dpm to pCi
7 = chemical yield for strontium
V = sample volume (L)
B2. The standard counting uncertainties for 89Sr (wcC(y4CSr89) ) and 90Sr (wcC(y4CSr90) ) are
calculated in units of pCi/L as follows:
— — — -IT- JT -TT-
2.22xXxVxY
/-•-» -. ^\
(B 1 6)
\ /
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/90,
Total Radiostrontium ( Sr) in Water: Rapid Method for High-Activity Samples
Ja2u (R i) + a2u (R ,
\_ V ' v ^' 2 v "-1
O/ — 0 00 T^ T^ T7
2.22x X xK x7
(B17)
OQ
___
B3. The combined standard uncertainties (CSU) for Sr and Sr are calculated as follows:
2(7) , by (a,
"Sr89
Sr90
2 u2(V) }U2(Y)
Sr90 y2 y2
r2
-il/2
(B18)
(B19)
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