EPA 402-R-10-001 c
www.epa.gov/narel
October 2011
Revision 0.1
Rapid Radiochemical Method for
Radiurn-226 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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Radium-226 in Water: Rapid Radiochemical Method for High-Activity Samples
Revision History
Revision 0
Revision 0.1
Original release.
• Corrected typographical and punctuation errors.
• Improve wording consistency with other methods.
• Added pH paper to list of equipment and supplies (6.9).
• Added 225Ra decay diagram to Section 17.4.
• Added Section 12.2.1 header (no change to process).
• Updated equations in sections 12.2.1 (At), 12.3 (ACa), and 12.3.2 (Sc),
to consistently apply factor for It (no impact on calculations).
• Updated equation objects in section 12.2.1 (equation for At) since
MSWord Equation Editor ensure that minus signs would be displayed).
• Updated footnote 9 to further clarify origin of critical value and
minimum detectable concentration formulations.
• Updated values in Table 17.2 to reflect 217At concentration (no impact
on calculations in 12.2.1).
• Updated rounding example in 12.4.2.2 for clarity.
• Deleted Appendix A (composition of Atlanta tap water) as irrelevant.
Redesignated Appendix B ("Preparation and Standardization of 225Ra
Tracer Following Separation from 229Th") as Appendix A.
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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RADiUM-226 IN WATER:
RAPID METHOD TECHNIQUE FOR HIGH-ACTIVITY SAMPLES
1. Scope and Application
1.1. The method will be applicable to samples where contamination is either from known or
unknown origins. If any filtration of the sample is performed prior to starting the
analysis, filterable 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. This method uses rapid radiochemical separations techniques for the isotopic
determination of 226Ra in water samples following a nuclear or radiological incident.
Although the method can detect 226Ra concentrations 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 26Ra.
1.3. The method is specific for 226Ra and uses MnO2 fixed on a resin bed (MnO2 resin) to
separate radium from interfering radionuclides and matrix constituents with additional
separation using Diphonix® resin1 to improve selectivity by removing radioactive
impurities.
1.4. The method is capable of satisfying a required method uncertainty for 226Ra of 0.65
pCi/L at an analytical action level of 5 pCi/L. To attain the stated measurement quality
objectives (MQOs) (see Sections 9.3, 9.4, and 9.5), a sample volume of approximately
200 mL and count time of 4 hours are recommended. Application of the method must
be validated by the laboratory using the protocols provided in Method Validation Guide
for Qualifying Methods Used by Radiological Laboratories Participating in Incident
Response Activities (EPA 2009, reference 16.3). 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.
1.5. This method is intended to be used for water samples that are similar in composition to
996
drinking water. The rapid Ra 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 techniques may be possible.
2. Summary of Method
2.1. A known quantity of 225Ra is used as the yield determinant in this analysis. Since the
source of the suspected contamination may not be known, the sample is initially
digested using concentrated nitric acid, followed by volume reduction and conversion
to the chloride salt using concentrated hydrochloric acid. The solution is adjusted to a
neutral pH and batch equilibrated with MnC>2 resin to separate radium from some
radioactive and non-radioactive matrix constituents. Further selectivity is achieved
1 A polyfunctional cation exchange resin containing diphosphonic and sulfonic acid functional groups bonded to a
polystyrene/divinylbenzene spherical bead. (Available commercially from Eichrom Technologies, LLC, Lisle, IL,
60561).
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Radium-226 in Water: Rapid Radiochemical Method for High-Activity Samples
using a column which contains Diphonix® resin. The radium (including 226Ra) eluted
from the column is prepared for counting by microprecipitation with BaSO/i.
2.2. Low-level measurements are performed by alpha spectrometry. The activity measured
in the 226Ra region of interest is corrected for chemical yield based on the observed
917 99S
activity of the alpha peak at 7.07 MeV ( At, the third progeny of Ra). See Table
17.1 for a list of alpha particle energies of the radionuclides that potentially may be
seen in the alpha spectra.
3. Definitions, Abbreviations and Acronyms
3.1. Analytical Protocol Specifications (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 (micron range).
3.5. Multi-Agency Radiological Analytical Laboratory Protocols Manual (MARLAP) (see
Reference 16.4).
3.6. Measurement Quality Objective (MQO). The analytical data requirements of the data
quality objectives that are project- or program-specific and can be quantitative or
qualitative. These analytical data requirements 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 (MMR)- 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
as an absolute value is applicable at or below an AAL.
3.9. Relative Required Method Uncertainty (^MR)- The relative required method uncertainty
is the WMR divided by the AAL and is typically expressed as a percentage. It is
applicable above the action level.
3.10. Sample Test Source (STS). This is the final form of the sample that is used for nuclear
counting. This form is usually specific for the nuclear counting technique in the
method, such as a solid deposited on a filter for alpha spectrometry analysis.
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Radium-226 in Water: Rapid Radiochemical Method for High-Activity Samples
4. Interferences
4.1. Radiological:
4.1.1. All radium isotopes in addition to 226Ra are retained on MnC>2, as are thorium
isotopes. Unless other radium isotopes are present in concentrations greater than
approximately three times the 226Ra activity concentration, interference from
other radium alphas will be resolved when using alpha spectrometry. Method
performance may be compromised if samples contain high levels of radium
isotopes due to ingrowth of interfering decay progeny. Samples should be pre-
screened prior to aliquanting and appropriate limits established to control the
amount of activity potentially present in the aliquant.2
4.1.2. Decay progeny from the 225Ra tracer will continue to ingrow as more time
elapses between the separation of radium and the count of the sample. Delaying
the count significantly longer than a day may introduce a possible positive bias
in results near the detection threshold. When MQOs require measurements close
to detection levels, and coordinating sample processing and counting schedules
is not conducive to counting the sample within -36 hours of the separation of
radium, the impact of tracer progeny tailing into the 226Ra may be minimized
by reducing the activity of the 225Ra tracer that is added to the sample. This will
aid in improving the signal-to-noise ratio for the 226Ra peak by minimizing the
amount of tailing from higher energy alphas of the 225Ra progeny.
4.1.2.1. The amount of 225Ra added to the samples may be decreased, and the
time for ingrowth between separation and counting increased, to
ensure that sufficient 225Ac, 221Fr, and 217At are present for yield
corrections at the point of the count. Although this detracts from the
rapidity of the method, it does not detract from the potential for high
throughput.
4.1.2.2. The size of the sample aliquant can be increased without changing the
amount of tracer added.
99S ^
4.1.3. Optimally, a purified Ra tracer solution should be used when performing this
method.
4.1.3.1. When using a purified source of 225Ra, the beginning of decay for
225Ra is the activity reference date established during standardization
99S
of the Ra solution.
4.1.3.2. When a purified 225Ra tracer solution is not available, a solution
containing 225Ra in equilibrium with 229Th may be used as a tracer. In
this case, the 225Ra activity is supported only until thorium is removed
using Diphonix® resin during processing of the sample. When using
this variation of the method, the beginning of 225Ra decay is the point
when the sample has passed through the Diphonix® column.
2 For very elevated levels of radium isotopes, it is recommended that laboratories use "The Determination of
Radium-226 and Radium-228 in Drinking Water by Gamma-ray Spectrometry Using HPGE or Ge(Li) Detectors,"
Revision 1.2, December 2004. Available from the Environmental Resources Center, Georgia Institute of
Technology, 620 Cherry Street, Atlanta, GA 30332-0335, USA, Telephone: 404-894-3776.
3 Using a purified 225Ra tracer is the approach recommended for this method. See Appendix B for a method for
purification and standardization of 225Ra tracer from 229Th solution.
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Radium-226 in Water: Rapid Radiochemical Method for High-Activity Samples
NOTE: Recording the point in time of the beginning of 225Ra decay to within Vz
hour will introduce a maximum bias of 0.1% for this measurement.
4.1.4. Every effort should be made to use the purified 225Ra as a tracer. It is also
possible to use 225Ra in equilibrium with 229Th, which may be added to each
sample as a tracer.4 This approach requires complete decontamination of a
relatively high activity of 229Th by the Diphonix® column later in the method,
however, since the spectral region of interest (ROI) for 229Th slightly overlaps
that of 226Ra. Inadequate decontamination of 229Th will lead to high bias in the
99^ 99^
Ra result especially when the levels of Ra in the sample are below 1 pCi/L.
oo/r 99O
The spectral region above Ra corresponding to Th should be monitored as
a routine measure to identify samples where 2 9Th interference may impact
compliance with project MQOs. If problematic levels of 229Th are identified in
spectra, measures must be taken to address the interference. These might
include:
4.1.4.1. Separating 225Ra from 229Th prior to its use as a tracer. Using purified
225Ra tracer is the default approach recommended for running this
method since it will completely address any potential for interference
by removing the source of the problem.
4.1.4.2. Increasing the sample aliquant size without changing the amount of
tracer added will increase analyte signal and reduce the relative impact
of the interference to levels that may be amenable with project MQOs.
4.1.4.3. The absolute amount of 229Th added to the samples may be decreased,
as long as the time for ingrowth between separation and counting is
increased to ensure that sufficient 217At is present for yield corrections
at the point of the count. Although this detracts from the rapidity of the
method, it allows more flexibility in the timing of the count and does
not detract from the potential for high throughput.
4.1.4.4. Developing spill-down factors (peak overlap corrections) to correct for
the interference and account for additional uncertainty in the analytical
results. This is not a trivial determination and should be validated prior
to use.
99S 99O
4.1.5. When a solution containing Ra in equilibrium with Th is used as a tracer,
thorium is removed later in the processing of the sample. The equilibrium
between the 225Ra and 229Th is maintained only until the sample is loaded onto
the Diphonix® column. At this point, thorium and actinium are retained on the
column and the 225Ra activity in the eluate is unsupported and begins to decay.
4.2. Non-radiological:
4.2.1. Low conductivity water (<100 uS cm l) may cause low-yield issues with some
samples. This may be partially corrected for by increasing the conductivity with
calcium standard solution.
4 The single-laboratory validation for this method was performed successfully by adding 225Ra in secular equilibrium
with 229Th tracer. Using purified 225Ra will provide better method performance since it will eliminate any concern
about breakthrough of the high levels of 229Th added to each sample. See Appendix B of this method for a method
for separating (and standardizing) 225Ra tracer from 229Th solution.
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Radium-226 in Water: Rapid Radiochemical Method for High-Activity Samples
4.2.2. Concentrations of non-radioactive barium present significantly in excess of the
amount of barium carrier added for microprecipitation may severely degrade the
resolution of alpha spectra. The quality of spectra should be monitored for
evidence of decreased resolution. A decreased sample size (i.e., smaller) may
need to be selected or the barium carrier decreased or omitted if the presence of
these interferences leads to unacceptably degraded method performance.
4.2.3. High concentrations of non-radioactive calcium, magnesium or strontium in the
sample may not only overwhelm the ability of the MnO2 resin to effectively
exchange radium isotopes but also may degrade the alpha spectrometry peaks
and increase analytical uncertainty. A decreased sample size (i.e., smaller) may
need to be selected when the presence of these interferences leads to degraded
method performance. If it is anticipated that these elements or barium (see Step
4.2.2) are present in quantities exceeding a small fraction of the mass of calcium
or barium added in Steps 11.2.3 and 11.1.3, respectively, an analytical
determination may need to be performed separately so that the interference can
be accommodated.
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 the potential for cross contamination.
5.3. Procedure-Specific Non-Radiological Hazards:
5.3.1. Solutions of 30% H2O2 can rapidly oxidize organic materials and generate
significant heat. Do not mix large quantities of peroxide solution with solutions
of organic solvents as the potential for conflagration exists.
6. Equipment and supplies
6.1. Alpha spectrometer calibrated for use over the range of-3.5-10 MeV.
6.2. Centrifuge tubes, polypropylene, 50 mL, disposable; or equivalent.
6.3. Chromatography columns, polypropylene, disposable:
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Radium-226 in Water: Rapid Radiochemical Method for High-Activity Samples
6.3.1. 1.5 cm ID. x 15 cm, with funnel reservoir; or equivalent.
6.3.2. 0.8 cm ID. x 4 cm; or equivalent.
6.4. Filter stand and filter funnels.
6.5. Filter, 0.1 micron, ~25-mm diameter (suitable for microprecipitation).
6.6. Membrane filter, 0.45 micron, ~47-mm diameter.
6.7. Vacuum filtration apparatus.
6.8. Heat lamp, 250-300 watt, with reflectors mounted -25 cm above the base.
6.9. pH paper.
6.10. Petri dish or other suitable container for storing sample test sources.
6.11. Stainless steel planchets or suitable holders/backing for sample test sources - able to
accommodate a 25-mm diameter filter.
6.12. Glass beaker, 600-mL capacity.
6.13. Stirring hot plate.
6.14. Magnetic stir bar (optional).
6.15. Centrifuge bottle, polypropylene, 250 mL, disposable; or equivalent (optional).
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). For microprecipitation, all solutions used in microprecipitation should be
prepared with water filtered through a 0.45 um (or smaller) filter.
7.1. Ammonium sulfate, solid (NH/^SO/t, available commercially.
7.2. Barium carrier (nominally 0.5 mg/mL as Ba2+). May be purchased as an atomic
absorption standard and diluted, or prepared by dissolving 0.45 g reagent grade
barium chloride, dihydrate (BaCb^FbO) in water and diluting to 500 mL with water.
7.3. Bromthymol blue indicator solution: Dissolve 0.1 g of bromthymol blue in 16 mL of
0.01 M NaOH. Dilute to 250 mL with water.
7.4. Calcium nitrate solution (1000 ppm as calcium). May be purchased as an atomic
absorption standard and diluted or prepared by dissolving 2.5 g of calcium carbonate
(CaCOs) in 70 mL of concentrated nitric acid and diluting to 1 L with water.
7.5. Diphonix® resin, 100-200-um mesh size [available from Eichrom Technologies,
Lisle, IL].
7.6. Ethanol, reagent 95 % (C2H5OH), available commercially.
7.7. Hydrochloric acid (12 M): Concentrated HC1, available commercially.
7.7.1. Hydrochloric acid (2M): Add 170 mL of concentrated HC1 to 800 mL of
water and dilute to 1.0 L with water.
7.7.2. Hydrochloric acid (1M): Add 83 mL of concentrated HC1 to 800 mL of water
and dilute to 1.0 L with water.
7.8. Hydrogen peroxide, H2O2 (30 % w/w), available commercially.
7.9. Isopropanol, 2-propanol, (CsHyOH), available commercially.
7.9.1. Isopropanol (2-propanol), 20 % (v/v) in water: Mix 20 mL of isopropanol
with 80 mL of water.
7.10. Methanol (CH3OH), available commercially.
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Radium-226 in Water: Rapid Radiochemical Method for High-Activity Samples
7.11. MnO2 resin, 75-150 |j,m MnO2 particle size on non-functionalized polystyrene resin
beads of 100-200 mesh [available commercially from Eichrom Technologies, Lisle,
IL].
7.12. MnO2 stripping reagent: Add 2 mL of 30 % H2O2 per 100 mL of 2 M HC1. Prepare
fresh for each use.
7.13. Nitric acid (16 M): Concentrated HNCb, available commercially.
7.14. Sodium hydroxide (1 M): Dissolve 4 g of sodium hydroxide (NaOH) in 50 mL of
water and dilute the solution to 100 mL.
7.15. Ra-225 tracer in 1-M HC1 solution in a concentration amenable to accurate addition
of about 180 dpm per sample (generally about 150-600 dpm/mL).
7.15.1. Ra-225 may be purified and standardized using a 229Th / 225Ra generator as
described in Appendix A of this method.
7.15.2. Th-229 containing an equilibrium concentration of 225Ra has been
successfully used without prior separation of the 225Ra. However, this
approach may be problematic due to the risk of high result bias (see
discussion in Steps 4.1.4 - 4.1.5).
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, HNCb shall be added until the
solution pH is less than 2.0.
8.4. If the dissolved concentration of radium 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 project.
9.1.2. One method blank shall be run with each batch of samples. The laboratory
blank should consist of demineralized 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
barium in the sample, may compromise chemical yield measurements, or
overall data quality.
9.2.Sample-specific quality control measures
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9.2.1. Limits and evaluation criteria shall be established to monitor each alpha
spectrum to ensure that spectral resolution and peak separation is adequate
to provide quantitative results. When 229Th / 225Ra solution is added directly
to the sample, the presence of detectable counts between -5.0 MeV and the
996
upper boundary established for the Ra ROI generally indicates the
presence of 229Th in the sample, and in the 226Ra ROI. If the presence of
229Th is noted and the concentration of 226Ra is determined to be an order of
magnitude below the action limit or the detection threshold of the method,
take corrective actions to ensure that MQOs have not been compromised
(e.g., clean-up 225Ra tracer before adding, or re-process affected samples and
associated QC samples. See interferences sections Steps 4.1.4 - 4.1.5. for
discussion).
9.3. This method is capable of achieving a WMR of 0.65 pCi/L at or below an action level of
5.0 pCi/L. This may be adjusted in the event specific MQOs are different.
9.4. This method is capable of achieving a 99%. See Table 17.3).
11. Procedure
11.1. Initial Sample Treatment
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11.1.1. For each sample in the batch, aliquant 0.2 L of raw or filtered water into a
beaker.
Note: Smaller or larger aliquants may be used if elevated sample activity is present or
as needed to meet detection requirements or MQOs. Method validation must be
conducted using approximately the same volume as that to be used in sample analysis^
11.1.2. To each aliquant, add 10 mL of concentrated nitric acid per 100 mL of
sample.
11.1.3. To each sample aliquant, add 100 uL of 0.5 mg/mL (nominal) barium carrier
solution and approximately 180 dpm of 225Ra tracer solution. The initial
amount of 225Ra added as a tracer should be high enough so that the
resultant counting uncertainty of the 217At activity ingrown from the tracer is
five percent (5 %) or less during the allotted sample count time.
Note: The activity of 217At present at the midpoint of the count is used to calculate the
chemical yield for radium by back-calculating the activity of 225Ra recovered. The
initial amount of 225Ra added as tracer may need to be varied to accommodate
planned differences in the time that has elapsed between chemical separation and the
count, but the activity should be sufficient, and the count time long enough, to ensure
that the resultant counting uncertainty for the 217At peak is five (5 %) percent or less.
See the calculation for At, in Step 12.2 for calculation of ingrowth factor for 217At and
Table 17.2 for typical ingrowth factors for a series of ingrowth times.
11.1.4. Reduce the sample volume to -20% of the original volume by bringing the
solution to a gentle boil and evaporating.
11.1.5. Following this digestion, add 10 mL of concentrated hydrochloric acid, and
carefully evaporate the solution to incipient dryness.
11.1.6. Reconstitute the sample by adding 100 mL of 1-M HC1. The sample may be
gently heated if necessary to facilitate dissolution of residual salts.
11.2. Water Sample Preparation and Pre-concentration of Radium on MnO2 resin:
11.2.1. Add 100 mL of 1-M NaOH to each sample.
11.2.2. If particulate material is visible at this time, filter the sample through a 0.45-
|im filter. (Do not rinse the filter). The filter should be saved for possible
analysis for DRPs.
11.2.3. Add enough 1000 ppm calcium solution to the filtrate from Step 11.2.2 to
ensure that the final calcium concentration is about 10 ppm. For waters that
naturally have calcium in them above 10 ppm this step will be unnecessary.
11.2.4. Add a few drops of bromthymol blue indicator solution and adjust each
sample to neutral pH by carefully adding 1-M NaOH until the color changes
from yellow to blue-green.
Note: Adding too much base will overshoot the blue-green endpoint (indicated by blue
color). The amount of NaOH added in Step 11.2.4 may be adjusted by carefully
adding a small quantity of 1-M HC1 and 1-M NaOH as needed to reach a blue-green
endpoint.
11.2.5. The sample is equilibrated with -1.0 g MnC>2 resin for 0.5-1.5 hours. Two
options are provided:
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11.2.5.1. Option 1: Add -1.0 g MnO2 resin to a beaker containing the
neutralized sample. Cover with a watch glass and gently stir on a
magnetic stirrer for at least 30 minutes.
11.2.5.2. Option 2: Transfer the neutralized sample to a 250 mL centrifuge
bottle which contains -1.0 g MnO2 resin. Agitate the bottle gently
on a shaker or in a tumbler for at least 30 minutes.
Note: Two options are provided for contacting the sample with MnO2 resin.
The contact time noted above (30 minutes) is to be understood as a
minimum. Higher radium yields may be obtained with somewhat longer
contact times (up to 90 minutes).
Note: Excessive agitation of the resin may lead to abrasion and loss of some
MnO2 from the resin and result in degraded chemical yields. Although
sample quantitation is not significantly impacted since a 225Ra yield tracer is
used, uptake on the resin during this step should be reasonably optimized
by evaluating the process and time used and choosing a default optimal
conditions corresponding to a minimum of 80-85% uptake from a clean
water matrix.
11.2.6. Pour the suspension into a 1.5-cm ID. x 15-cm column fitted with a
reservoir funnel. Allow sample to pass through column. Rinse the walls of
the funnel reservoir and column with demineralized water. The combined
column effluent from this step may be discarded.
11.2.7. Place a clean 50 mL centrifuge tube under each MnO2 column. Add 10 mL
of freshly made MnO2 Stripping Reagent to the MnO2 column to elute
radium and other elements. Catch the column eluate containing radium and
retain for subsequent processing.
Note: Effervescence will be noted upon addition of the MnO2 Stripping Reagent.
Gently tapping the column to dislodge any bubbles that form will help minimize
channeling and may improve radium recovery. The resin bed will become light pink in
color as MnO2 dissolves.
11.3. Actinium and Thorium Removal Using Diphonix® resin:
11.3.1. Prepare a Diphonix® resin column for each sample to be processed as
follows:5
11.3.1.1. Slurry -1.0-g Diphonix® resin per column in water.
11.3.1.2. Transfer the resin to the 0.8-cm ID. x 4-cm columns to obtain a
uniform resin bed of-1.4-1.6 mL (bed height -26-30 mm). A top
column barrier (e.g., frit, glass wool, beads) may be used to
minimize turbulence that may disrupt the resin bed when adding
solution to the column.
11.3.2. Precondition the column by passing 20 mL of 2-M HC1 through the column
discarding the column effluent.
11.3.3. Place a clean 50-mL centrifuge tube under each Diphonix® column.
5 Commercially supplied pre-packed columns may be used here. When packing columns using bulk resin, excessive
resin fines should be removed by rinsing the resin one or more times with an excess of water and decanting the
water containing the fines prior to transferring the material to the column.
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11.3.4. Swirl the solution retained in Step 11.2.7 to remove bubbles and carefully
load onto the column taking care to minimize disturbing the resin bed.
Collect column effluents in the 50-mL centrifuge tube. Allow the solution to
flow by gravity.
11.3.5. When the load solution has stopped flowing (or is below the top of the resin
bed), rinse the column with two 5-mL volumes of 2-M HC1. Collect the
rinse solutions in the same 50-mL centrifuge tube (the total volume will be
approximately 20 mL).
11.3.6. Record the date and time of the last rinse (Step 11.3.5) as the date and time
of separation of radium from parent and progeny. This is also the beginning
of ingrowth of 225Ac (and 221Fr and 217At).
Note: If purified 225Ra tracer is added to the sample (see Step 10.2 and Appendix A),
the 225Ra activity was unsupported before the tracer solution was added to the sample.
The activity reference date and time established during standardization of the 225Ra
tracer is used as the reference date for the 225Ra solution.
Note: If 225Ra at some degree of secular equilibrium with 229Th is added as tracer in
the initial step, the activity of 225Ra is dependent upon the total amount of time
between the last 229Th purification and Stepll.3.6. The decay of 225Ra starts at Step
11.3.6.
®
Note: The Diphonix resin contains thorium, actinium and possibly other
radionuclides present in the sample and should be disposed of according to applicable
laboratory procedures.
99^
11.4. Barium sulfate micro-precipitation of Ra
11.4.1. Add ~3.0 g of (NH4)2SO4 to the 20 mL of 2M HC1 solution collected from
the Diphonix column in Steps 11.3.3 - 11.3.5. Mix gently to completely
dissolve the salt (dissolves readily).
11.4.2. Add 5.0 mL of isopropanol and mix gently (to avoid generating bubbles).
11.4.3. Place in an ultrasonic bath filled with cold tap water (ice may be added) for
at least 20 minutes.
11.4.4. Pre-wet a 0.1 -micron filter using methanol or ethanol. Filter the suspension
through the filter using vacuum. The precipitate will not be visually
apparent.
11.4.5. Rinse the sample container and filter apparatus with three 2-mL portions of
20% isopropanol solution to dissolve residual (NFL^SO/i. Allow each rinse
to completely pass through filter before adding the subsequent rinse.
11.4.6. Rinse the filter apparatus with about 2 mL of methanol or ethanol to
facilitate drying. Turn off vacuum.
11.4.7. Carefully remove the filter and place it face-side up in a Petri dish. Carefully
dry under a heating lamp for few minutes. Avoid excessive heat which may
cause the filter to curl or shrink.
11.4.8. Mount the dried filter on a support appropriate for the counting system to be
used.
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917
11.4.9. Store the filter for at least 24 hours to allow sufficient At (third progeny
of 225Ra) to ingrow into the sample test source allowing a measurement
uncertainty for the 217At of < ~5 %.
11.4.10. Count by alpha spectrometry. The count times should be adjusted to meet
the uncertainties and detection capabilities identified in Steps 9.3, 9.4, and
9.5.
12. Data Analysis and Calculations
12.1. The final sample test source (filter mounted on a planchet) will need to have at least a
24-hour ingrowth for 225Ac (and 221Fr and 217At) to meet Analytical Protocol
Specifications for chemical yield with a counting time of 4 hours. At-217 (third
progeny of 225Ra) has a single, distinct alpha peak with a centroid at 7.067 MeV and
is used for determining the yield.
Note: Actinium 225 and other decay progeny from the 225Ra (e.g., 217At) tracer will continue to
ingrow as time elapses between separation and the count of the sample. Delaying the count
significantly longer than a day may introduce a possible positive bias in results near the detection
threshold. When sample counting will be delayed longer than 36 hours, and MQOs foresee
decisions being made close to detection levels, the impact of tracer progeny tailing should be
minimized. Possible approaches for accomplishing this may include improving the signal to noise
ratio by: 1) Processing a larger sample aliquant; 2) Decreasing the tracer activity added to a level
that will still provide adequate statistics ~400-1500 net counts at the time of the analysis but will
minimize spilldown into the 226Ra ROI.
12.2. While the radiochemical yield is not directly used to determine the 226Ra activity of
the sample, the following equation can be used to calculate the radiochemical yield
(see Reference 16.6), if required:
R -Rh
RY= ' b
sxAtx!t
Where:
99S 917
RY = Fractional radiochemical yield based on Ra (from ingrown At
at 7.07 MeV)
Rt = Total count rate beneath the 217At peak at 7.07 MeV, cpm
Rb = Background count rate for the same region, cpm
e = Efficiency for the alpha spectrometer
/t = Fractional abundance for the 7.07 MeV alpha peak counted (=
0.9999)
917
A\ = Activity (dpm) of At at midpoint of the count (see step 12.2.1)
Note: If 225Ra is separated from 229Th for use as a purified tracer, the 225Ra activity is
unsupported and begins to decay at the point of separation from 229Th, and not in Step 11.3.6.
Instead, the reference date and time established when the tracer is standardized is used for decay
correction of the 225Ra activity. If 229Th solution (with 225Ra in full secular equilibrium) is added
to the sample, the 225Ra activity is equal to the 229Th activity added and only begins to decay at
the point of separation of 225Ra from 229Th in Step 11.3.6.
12.2.1. Activity of 217Ac at the midpoint of the count interval.
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917
A\ = The activity of At at midpoint of the count (the target value that
should be achieved for 100% yield), in dpm.
= 3.0408(^225RJ [e-Xld-e-M]
99S f\
^225Ra = Activity in dpm of Ra tracer added to the sample in Step 11.1.3
decay corrected to the date and time of radium separation in Step
11.3.6.
d = Elapsed ingrowth time for 225Ac [and the progeny 217At], in days
from the date and time of Ra separation to the midpoint of the
sample count
AI = 0.04652 d'1 (decay constant for 225Ra - half-life = 14.9 days)
X2 = 0.06931 d'1 (decay constant for 225Ac) - half-life = 10.0 days)
3.0408 = /12 /(/12 - /^ ) [a good approximation as the half lives of 221Fr and
917 99S
At are short enough so that secular equilibrium with Ac is
ensured]
12.3. The activity concentration of an analyte and its combined standard uncertainty are
calculated using the following equations:
ACa =
and
Fax^ntxJDax/ax2.22
where:
^4Ca = activity concentration of the analyte at time of count, (pCi/L)
Rna = net count rate of the analyte in the defined region of interest (ROI),
in counts per minute (Note that the peaks at 4.784 and 4.602 MeV
are generally included in the ROI for 226Ra)
6 When separated 225Ra tracer is added to the sample, its initial activity, ^sRa-mitmi, must be corrected for decay from
he refen
follows:
the reference date established during standardization of the tracer to the point of separation of 225Ra and225 Ac as
where: k\ = decay constant for 225Ra (0.04652 d"1); and dt = time elapsed between the activity reference date for the
225Ra tracer solution added to the sample and the separation of 225Ra and 225Ac in Step 11.3.6 (days).
When 229Th containing ingrown 225Ra is added directly to the sample, the amount of 225Ra ingrown since purification
of the 229Th solution is calculated as:
where: A229ih = Activity of the 229Th standard on the date of the separation of Th and Ra (Step 11.3.6); ^ = decay
constant for 225Ra (0.04652 d"1); and d, = time elapsed between the purification of 229Th solution added to the sample
and the separation of 225Ra and 229Th/225Ac in Step 1 1.3.6 (days).
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917
A\ = the activity of At at midpoint of the count that should be
achieved for 100% yield, in dpm (see Step 12.2 for detailed
calculation)
/t = Fractional abundance for the 7.07 MeV alpha peak counted (=
0.9999)
Rnt = net count rate of the tracer in the defined ROI, in counts per minute
Va = volume of the sample aliquant (L)
Da = correction factor for decay of the analyte from the time of sample
collection (or other reference time) to the midpoint of the counting
period, if required
/a = probability of a emission for 226Ra (The combined peaks at 4.78
and 4.602 MeV are generally included in the ROI with an
abundance of LOO.)1
uc(ACz) = combined standard uncertainty of the activity concentration of the
analyte (pCi/L)
u(Ai) = standard uncertainty of the activity of the tracer added to the
sample (dpm)
z/(Fa) = standard uncertainty of the volume of sample aliquant (L)
w(Rna) = standard uncertainty of the net count rate of the analyte in counts
per minute
u(RDt) = standard uncertainty of the net count rate of the tracer in counts per
minute
Note: The uncertainties of the decay-correction factors and of the probability of decay factors
are assumed to be negligible.
Note: The equation for the combined standard uncertainty (wc(^4Ca)) calculation is arranged to
eliminate the possibility of dividing by zero if Ra = 0.
Note: The standard uncertainty of the activity of the tracer added to the sample must reflect that
associated with the activity of the standard reference material and any other significant sources
of uncertainty such as those introduced during the preparation of the tracer solution (e.g.,
weighing or dilution factors) and during the process of adding the tracer to the sample.
12.3.1 The net count rate of an analyte or tracer and its standard uncertainty can be
calculated using the following equations:
r r
n _ *-"x *-b
tb
and
where:
o
Rnx = net count rate of analyte or tracer, in counts per minute
7 If only the individual peak at 4.78 MeV is used, and completely resolved from the 4.602 MeV peak, the abundance
would be 0.9445.
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Cx = sample counts in the analyte or the tracer ROI
ts = sample count time (min)
Cbx = background counts in the same ROI as for x (x refers to the
respective analyte or tracer count)
tb = background count time (min)
w(^nx) = standard uncertainty of the net count rate of tracer or
analyte, in counts per minute
12.3.2 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.9
(1
u
Stapleton
--1 +^x 1 + f- +z:_ a](Rbatb+dstapleton]
X At X /,
When the Type I decision error rate, a, equals 0.05, z\.a = 1.645, and the constant, dstapieton,
from the Stapleton approximation is set to 0.4, the expression above becomes:
S =
0.4x ^-1 + 0.677x 1 + ^ +1.645x l(Rbatb + 0.4)x^x 1
Vb ) \ tb} V tb {_
tsxVaxRntxDax!a
MDC =
x At x 7t
8 For methods with very low counts, MARLAP Section 19.5.2.2 recommends adding one count each to the gross
counts and the background counts when estimating the uncertainty of the respective net counts. This minimizes
negative bias in the estimate of uncertainty and protects against calculating zero uncertainty when a total of zero
counts are observed for the sample and background.
9 The formulations for the critical level and minimum detectable concentrations are as recommended in MARLAP
Section 20A.2.2, Equation 20.54, and Section 20A.3.2, 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, /?, equals 0.05, z\-p = 1.645, the expression above becomes:
MDC =
2.71 x
3.29xjft t. x
x 4 x /t
where:
Rba
i_a
background count rate for the analyte in the defined ROI, in counts
per minute
the 1-a quantile of the normal standard distribution
the 1-6 quantile of the normal standard distribution
12.4 Results Reporting
12.4. 1 The following data should be reported for each result: volume of sample
used; yield of tracer and its uncertainty; and full width at half maximum
(FWHM) of each peak used in the analysis.
12.4.2 The following conventions should be used for each result:
12.4.2.1 Result in scientific notation ± combined standard uncertainty.
12.4.2.2 If solid material was filtered from the solution and analyzed
separately, the results of that analysis should be reported separately
as pCi/L of the original volume from which the solids were filtered
if no other guidance is provided on reporting of results for the
solids. For example:
226Ra for Sample 12-1-99:
Filtrate Result: (1.28 ± 0.15) x 101 pCi/L
Filtered Residue Result: (2.50 ± 0.32) 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 for an individual sample is -35 hours and per batch is -38
hours.
®
14 Pollution Prevention
14. 1 The use of MnO2 and Diphonix resin reduces the amount of solvents that would
otherwise be needed to co-precipitate and purify the final sample test source.
1 5 Waste Management
15.1 Nitric acid and hydrochloric acid wastes should be neutralized before disposal and
then disposed of in accordance with local ordinances.
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15.2 All final precipitated materials contain tracer and should be dealt with as radioactive
waste and disposed of in accordance with the restrictions provided in the facility's
NRC license.
16 References
16.1 RAW04-10, "Radium-226/228 in Water (MnO2 Resin and DGA Resin Method),"
Eichrom Technologies, Lisle Illinois (June 2006).
16.2 A Rapid Method For Alpha-Spectrometric Analysis of Radium Isotopes in Natural
Waters Using Ion-Selective Membrane Technology; S. Purkl and A. Eisenhauer.
Applied Radiation and Isotopes 59(4):245-54 (Oct 2003).
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 04-001 A, 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 S. Purkl and A. Eisenhauer (2003). "A Rapid Method for Alpha-Spectrometric
Analysis of Radium Isotopes in Natural Waters Using Ion-Selective Membrane
Technology." Applied Radiation and Isotopes 59(4):245-54.
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17 Tables, Diagrams, and Flow Charts
17.1 Tables [including major radiation emissions from all radionuclides separated]
Table 17.1 Alpha Particle Energies and Abundances of Importance
Energy
(MeV)
4.601
4.784
4.798
4.815
4.838
4.845
4.901
4.968
4.979
5.053
5.434
5.449
5.489
5.540
5.580
5.607
5.609
5.637
5.682
5.685
5.716
5.724
5.732
5.732
5.747
Abundance
(%)
5.6
94.5
1.5
9.3
5.0
56.2
10.2
6.0
3.2
6.6
2.2
5.1
99.9
9.0
1.2
25.2
1.1
4.4
1.3
94.9
51.6
3.1
8.0
1.3
9.0
Nuclide
Ra-226
Ra-226
Th -229
Th -229
Th -229
Th -229
Th -229
Th -229
Th -229
Th -229
Ra-223
Ra-224
Rn-222
Ra-223
Ac -225
Ra-223
Ac -225
Ac -225
Ac -225
Ra-224
Ra-223
Ac -225
Ac -225
Ac -225
Ra-223
- Analyte
Energy
(MeV)
5.791
5.793
5.830
5.869
6.002
6.051
6.090
6.126
6.243
6.278
6.288
6.341
6.425
6.553
6.623
6.778
6.819
7.067
7.386
7.450
7.687
8.376
8.525
11.660
Abundance
(%)
8.6
18.1
50.7
1.9
100.0
25.1
9.8
15.1
1.3
16.2
99.9
83.4
7.5
12.9
83.5
100.0
79.4
99.99
100.0
98.9
100.0
100.0
2.1
96.8
Nuclide
Ac -225
Ac -225
Ac -225
Bi-213
Po -218
Bi-212
Bi-212
Fr-221
Fr-221
Bi-211
Rn-220
Fr-221
Rn-219
Rn-219
Bi-211
Po -216
Rn-219
At -217
Po -215
Po-211
Po -214
Po -213
Po -212
Po -212
217
At (3rd progeny of 225Ra tracer)
I I - 229Th (Check ROI for indications of inadequate clean-up)
Includes only alpha particles with abundance > 1%.
Reference: NUDAT 2.4, Radiation Decay National Nuclear Data Center, Brookhaven National
Laboratory; Available at: www. nndc. bnl.gov/nudat2/mdx dec.jsp; Queried: November 11, 2007.
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17.2 Ingrowth curves and Ingrowth factors
1000
Ac-225 In-Growth in Ra-225
0 200
400 600
Time, Hours
800 1000
ocn _,
onn t
•i^n -
Q.
"° inn -
en
Op
c
Ra-225 In-Growth in Th-229
jT
f
I
} 20 40 60 80 100 V.
Days
—»— Th-229, dpm
— B — Ra-225, dpm
10
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Table 17.2. Ingrowth Factors for 217At in 225Ra
Time elapsed between
separation of Ra and
midpoint of count
in hours
Ingrowth Factor*
Time elapsed between
separation of Ra and
midpoint of count
in hours
Ingrowth Factor*
1
0.002867
72
0.1748
2
0.005734
96
0.2200
3
0.008588
120
0.2596
4
0.01143
144
0.2940
5
0.01425
192
0.3494
6
0.01707
240
0.3893
24
0.06540
360
0.4383
48
0.1235
480
0.4391
'ingrowth Factor represents the fraction of Ac activity at the midpoint of the sample count relative to the Ra
activity present at the date/time ofRa separation. These ingrowth factors may be closely approximated (within a
fraction of a percent) using the expression for At in Step 12.2.1.
Table 17.3 Ingrowth Factors for 225Ra in 229Th
Time elapsed between
purification of the 229Th
standard and date of Ra
separation
in days
Ingrowth Factor*
Time elapsed between
purification of the 229Th
standard and date of Ra
separation
in days
Ingrowth Factor*
1
0.04545
50
0.9023
5
0.2075
55
0.9226
10
0.3720
60
0.9387
12
0.4278
70
0.9615
15
0.5023
80
0.9758
20
0.6056
90
0.9848
25
0.6875
100
0.9905
27
0.7152
130
0.9976
30
0.7523
160
0.9994
40
0.8445
200
0.9999
Ingrowth Factor represents the fraction Ra activity/ Th activity at the time ofRa separation.
225-,
Table 17.4 Decay Factors for Unsupported Ra
Time elapsed
between separation
of229Thand225Ra
in days
Decay Factor*
Time elapsed
between separation
of229Thand225Ra
in days
Decay Factor*
1
0.9545
50
0.09769
5
0.7925
55
0.07741
10
0.6280
60
0.06135
12
0.5722
70
0.03853
15
0.4977
80
0.02420
20
0.3944
90
0.01519
25
0.3125
100
0.00954
27
0.2848
130
0.00236
30
0.2477
160
0.00059
40
0.1555
200
0.00009
Decay Factor represents the fraction Ra activity remaining as calculated using the equation in Footnote 6.
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17.3 Example Alpha Spectrum from a Processed Sample
100-.
5000
218PoV21W
— background
- 1 I ground water
o Th-series
e Np-series
: U-Ra-series
Ac-series
6000
7000
8000
9000
Energy/keV
Reference: Purkl, Stefan, Dissertation: Entwicklung und Anwendung neuer analytischer Methoden zur
schnellen Bestimmung von kurzlebigen Radiumisotopen und Radon im Grundwasserbeeinflussten Milieu der
Ostsee; Chapter 2, Figure 3; Christian-Albrechts Universitaet, Kiel, Germany, 2003.
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17.4 Decay Schemes for Analyte and Tracer
a
164
22.2 y
P
226Ra Decay Scheme
Secular equilibrium is
established between 228Ra
and 222Rn in about 18 days.
1 h
3.1 min
a
27 min
P
1,600y
a
3.8 d
a
It takes about 4 hours for secular
equilibrium to be established
between 222Rn and 214Po after
fresh 222Rn is separated.
225Ra (Including Parent) Decay Scheme
45.6 min
P
4.8 min
a
a
10.0 d
a
7.3x103a
14.9 d
Secular Equilibrium between
229Thand225Rais achieved
after about 70 days.
The short half-lives of 221Fr and 217At allow the
32 ms 217 At activity to be calculated from 225Ac activity
based on secular equilibrium with 225Ac.
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17.5 Flowchart
Note: Shaded figures are associated with the timeline.
11.1.1 to 11.1.5
Aliquant sample.
Add nitric acid,
tracer and barium
carrier and digest.
Reduce volume.
Separation Scheme and Timeline for 226Ra
11.3.1 to 11.3.2
Prepare and pre-
condition Diphonix
column.
11.1.6
Reconstitute with
with 1 00 ml
oflMHCL
11.2.5.1 or 11.2.5.2
Equilibrate sample
with MnO2 resin for
30-90 min.
11.2.1 to 11.2.4
Add NaOH and filter
to remove particulates.
Add calcium nitrate.
Add indicator and adjust
pH to neutral.
11.2.6
Transfer MnO2
resin to a column.
Rinse with
demineralized water.
Discard eluent.
11.3.3to 11.3.4
Load solution from MnO2 onto
Diphonix® column and
allow to gravity drain.
Elute with two more 5-mL
aliquantsof 2M HCI.
11.2.7
Add 10 ml
2M HCI/0.6% H2O2
to strip analytefrom
MnO2 resin into
centrifuge tube.
11.3.5
Collect, load, and rinse
eluates containing
radium.
11.4.1 to 11.4.6
Add ammonium sulfate,
isopropanol.and
ultrasonicate
to ppt Ra/BaSO4.
11.4.7to 11.4.10
Filter, dry and
mount precipitate.
Start count.
1 2.5
Timeline (Hours)
7.
30
34
37
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Appendix A:
Preparation and Standardization of Ra Tracer Following Separation from 229Th
Al. Summary Description of Procedure
This procedure describes a 225Ra generator to make tracer amounts of 225Ra using a 229Th
solution. Th-229 is separated from 225Ra using Y(OH)3 co-precipitation. Th-229 is carried in the
precipitate and most of the 225Ra remains in solution. Centrifugation to remove 229Th in the
99S 90S
precipitate and filtration of the supernate produces the Ra tracer solution. The Ra activity of
the tracer solution is standardized by counting sample test sources prepared from at least five
replicate aliquants of the 225Ra solution, each spiked with a known quantity of a 226Ra standard.
This standardized activity concentration, referenced to the date and time of the 225Ra separation
described in Step 4.11.7 below, is then decay-corrected to the date and time of subsequent
sample analyses.
ooc
The Y[Th](OH)3 precipitate may be stored and re-used later to generate more Ra tracer
solution. 225Ra ingrows in the 229Th fraction (Y(OH)3 precipitate) and after 50 days will be about
90% ingrown. After sufficient ingrowth time 22 Ra may be harvested to make a fresh 225Ra tracer
solution by dissolving the precipitate and re-precipitating Y(OH)3 to separate 229Th from 225Ra.
Multiple 225Ra generators may be prepared to ensure that 225Ra tracer will be continuously
available. The 225Ra tracer solution produced is usable for 2-3 half-lives (-30-45 days). To
minimize effort involved with standardization of the 225Ra solution, it is recommended that the
laboratory staff prepare an amount of 229Th sufficient to support the laboratory's expected
workload for 3-5 weeks. Since the 229Th solution is reused, and the half-life of 229Th is long
OOP
(7,342 years), the need to purchase a new certified Th solution is kept to a minimum.
A2.Equipment and Supplies
A2.1. Refer to Section 6 of the main procedure.
A3.Reagents and Standards
A3.1. Refer to Section 7 of the main procedure.
A4. Procedure
A4.1. Add a sufficient amount of 229Th solution (that which will yield at least 150-600
dpm/mL of the 225Ra solution) to a 50-mL centrifuge tube.10
A4.2. Add 20 mg Y (2 mL of 10 mg/mL Y metals standard stock solution).
A4.3. Add 1 mg Ba (0.1 mL of 10 mg/mL Ba metals standard stock solution).
A4.4. Add 4 mL of concentrated ammonium hydroxide to form Y(OH)3 precipitate.
A4.5. Centrifuge and decant the supernatant into the open barrel of a 50-mL syringe, fitted
with a 0.45-|im syringe filter. Hold the syringe barrel over a new 50-mL centrifuge
tube while decanting. Insert the syringe plunger and filter the supernatant into the new
centrifuge tube. Discard the filter as potentially contaminated rad waste.
10 For example, if 40 mL of a 229Th solution of 600 dpm/mL is used, the maximum final activity of 225Ra will be
-510 dpm/mL at Step A4.8. This solution would require about 1.4 mL for the standardization process and about 8
mL for a batch of 20 samples.
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Radium-226 in Water: Rapid Radiochemical Method for High-Activity Samples
A4.6. Cap the centrifuge tube with the precipitate, label clearly with the standard ID,
precipitation date, and the technician's initials and store for future use.
A4.7. Properly label the new centrifuge tube with the supernate. This is the 225Ra tracer
solution.
99S
A4.8. Add 3 mL of concentrated HC1 to Ra tracer solution. Cap centrifuge tube and mix
well.
A4.9. Prepare the following solutions in 10 mL of 2-M HC1 for standardization of 225Ra
tracer.
Solution Spike(s)
Standardization -80 dpm of the 225Ra tracer solution, and
Replicates ~8 dpm of a 226Ra standard traceable to NIST or
(5 replicates) equivalent
Blank -80 dpm of the 225Ra tracer solution (the blank
should be evaluated to confirm that 226Ra is not
detected in the 225Ra tracer solution at levels that
may compromise sample results when used in the
method)
99S
Standardization -80 dpm of the Ra tracer solution, and
Control Sample -8 dpm of a second source independent traceable
226Ra standard (the Standardization Control Sample
should be evaluated to confirm that the standardiza-
tion process does not introduce significant bias into
the standardized value for the 225Ra tracer)
A4.10. Add 75 |ig Ba (0.075 mL of 1000 |ig/mL Ba) to all solutions.
A4.11. Process the solutions to prepare sources for alpha spectrometry as follows:
A4.11.1. Slurry -1.0 g of Diphonix® resin per column in water.
A4.11.2. Transfer the resin to 0.8 cm (ID.) x 4 cm columns to obtain a uniform
resin bed.
A4.11.3. Precondition the columns by passing 20 mL 2 M HC1 through the
columns. Discard the effluent.
A4.11.4. Place clean 50-mL centrifuge tubes under the columns.
A4.11.5. Load the solutions from Step A4.10 onto the columns. Collect the
effluents in the 50-mL centrifuge tubes. Allow the solutions to flow by
gravity.
A4.11.6. When the load solutions have stopped flowing, rinse columns with two 5-
mL volumes of 2-M HC1. Collect the rinse solutions in the same 50-mL
centrifuge tubes (the total volume will be about 20 mL).
A4.11.7. Record the date and time of the last rinse as the date and time of
separation of radium (beginning of 225Ac ingrowth).
A4.11.8. Add -3.0 grams of (NH4)2SO4 to the solutions from Step A4.11.6. Mix
gently to dissolve.
A4.11.9. Add 5.0 mL of isopropanol and mix gently.
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A4.11.10. Place in an ultrasonic bath filled with cold tap water for at least 20
minutes.
A4.11.11. Filter the suspensions through pre-wetted (using methanol or ethanol) 0.1-
um filters.
A4.11.12. Rinse the filters with three 2-mL portions of 20% isopropanol. Allow each
rinse to completely pass through filter before adding the next rinse.
A4.ll.13. Rinse each filter with about 2 mL of methanol or ethanol.
A4.11.14. Carefully place each filter face-side up on a labeled stainless steel
planchet, or other suitable source mount, which has previously been
prepared with an appropriate adhesive (e.g., double stick tape).
A4.11.15. Dry under a heat lamp for a few minutes.
A4.11.16. After allowing about 24-hours ingrowth, count the standardization sources
by alpha spectrometry.
A4.12. Calculate the activity of 225Ra, in units of dpm/mL, in the standardization replicates,
at the 225Ra time of separation as follows:
A7
(N*»At ^b]
V tmAt *b ,
X(A™Ra
)x(^J
[(3.0408)(/() (e 2ld -e ^l
where:
99S
A = Activity concentration of Ra, in dpm/mL [at the time of separation from
229Th, Step A4.11.7]
217 = Total counts beneath the 217At peak at 7.07 MeV
= Total counts beneath the 226Ra peak at 4.78 MeV
Nb = Background count rate for the corresponding region of interest,
4 = Duration of the count for the sample test source, minutes
tb = Duration of the background count, minutes
A = Activity of 226Ra added to each aliquant, in dpm/mL
226Ra
99^
V226 = volume of Ra solution taken for the analysis (mL)
99S
F225 = volume of Ra solution taken for the analysis (mL)
ooc 917
d = Elapsed ingrowth time for Ac [and the progeny At], from separation to
the midpoint of the sample count, days
AI = 0.04652 d'1 (decay constant for 225Ra - half-life = 14.9 days)
A2 = 0.06931 d'1 (decay constant for 225Ac) - half-life = 10.0 days)
/t = Fractional abundance for the 7.07 MeV alpha peak counted (= 0.9999)
3.0408 = X2d/(X2d - \d) [a good approximation as the half lives of 221Fr and 217At are
99S
short enough so secular equilibrium with Ac is ensured]
Note: The activity of the separated /422SRa will need to be decay corrected to the point of separation in the
main procedure (Step 11.3.6) so that the results can be accurately determined.
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225T
A4.13. Calculate the uncertainty of the activity concentration of the Ra tracer at the
reference date/time:
where:
226Ra
Nb
4
tb
V,
/,
V
d
226Ra
,™ )
226Ray
25Ra
225Ra
3.0408
'^AL + ^t_
-^M xfe.CMOgx/,,,,
j L A
- + ACl, x
225 Ra
= Standard uncertainty of the activity concentration of 225Ra, in dpm/mL
= Total counts beneath the 217At peak at 7.07 MeV,
99^
= Total counts beneath the Ra tracer peak at 4.78 MeV
= Background count rate for the corresponding region of interest,
= Duration of the count for the sample test source, minutes
= Duration of the background count, minutes
99^
= Activity of Ra added to each aliquant, in dpm/mL
= Activity of 225Ra, in dpm/mL
= Volume of 226Ra solution taken for the analysis (mL)
= Volume of 226Ra solution taken for the analysis (mL)
= Fractional abundance for the 226Ra peak at 4.78 MeV (= 1.000)
99S
= Volume of Ra solution taken for the analysis (mL)
99S
= Volume of Ra solution taken for the analysis (mL)
= Elapsed ingrowth time for 225Ac [and the progeny 217At], from separation to
the midpoint of the sample count, days
= 0.04652 d"1 (decay constant for 225Ra - half-life = 14.9 days)
= 0.06931 d"1 (decay constant for 225Ac) - half-life = 10.0 days)
= Fractional abundance for the 7.07 MeV alpha peak counted (= 0.9999)
= h2d/(h2d - \d] [a good approximation as the half lives of221Fr and 217At
are short enough so secular equilibrium with 225Ac is ensured]
= Standard uncertainty of net count rate for 226Ra, in cpm
= Net count rate for 226Ra, in (cpm)
Note: The uncertainty of half-lives and abundance values are a negligible contributor to the combined
uncertainty and are considered during the evaluation of combined uncertainty.
A4.14. Calculate the mean and standard deviation of the mean (standard error) for the
replicate determinations, to determine the acceptability of the tracer solution for use.
The calculated standard deviation of the mean should be equal to or less than 5% of
the calculated mean value.
A4.15. Store the centrifuge tube containing the Y(OH)3/Th(OH)4precipitate. After sufficient
time has elapsed a fresh 225Ra tracer solution may be generated by dissolving the
precipitate with 40 mL of 0.5-M HNOs and repeating Steps B4.3 through B4.9 of this
Appendix.
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