Validation of Rapid Radiochemical Method for Californium-252 in Water, Air Particulate Filters, Swipes and Soils for Environmental Remediation Following Radiological Incidents

Validation of Rapid Radiochemical Method for Californium-252 in Water, Air
Particulate Filters, Swipes and Soils for Environmental Remediation Following
Radiological Incidents
Analyte(s)
CAS RN®
Californium-252
13981-17-4
Analysis Purpose: Qualitative analysis
Technique: Alpha spectrometry
Method Developed for: Californium-252 (252Cf) in water, air particulate filter, swipes and soil samples
Method Selected for: SAM will list this method for qualitative analysis of water, air particulate filter,
swipes and soil matrices.
Description of Method: This method is based on the use of extraction chromatography resins (TEVA® +
DGA® resins) to isolate and purify californium by removing interfering radionuclides as well as other
matrix components. The method utilizes vacuum-assisted flow to improve the speed of the separations.
Americium-243 (243Am) tracer equilibrated with the sample is used as a yield monitor.
• Water samples are concentrated using a calcium phosphate [Ca3(PC>4)2] coprecipitation. The calcium
phosphate precipitate is dissolved in a load solution containing ~3 Molar (M) nitric acid (HNO3) -1M
aluminum nitrate [AI(NC>3)3] before continuing with chemical separations.
• Glass-fiber or cellulose-based air particulate filter samples are wet-ashed with repeated additions of
nitric and hydrofluoric acids and hydrogen peroxide. The residues are treated with nitric-boric acid,
and dissolved in a load solution containing 3M HNO3 - 1M AI(NC>3)3 before continuing with chemical
separations.
• Cotton-twill swipe and organic-polymer-based air particulate filter samples are dry-ashed in a beaker
for 30-60 minutes using a ramped program to minimize the risk of flash-ignition. The residue is
transferred to a Teflon beaker with nitric acid and hydrogen peroxide, digested with hydrofluoric acid,
and taken to dryness. The residues are wet-ashed with nitric acid and hydrogen peroxide and taken
to dryness before being treated with nitric-boric acid and dissolved in a load solution containing 3M
HNO3 -1M AI(N03)3 for chemical separations.
• Soils are finely ground before being fused with sodium hydroxide (NaOH) in zirconium crucibles. The
fusion cake is dissolved in water and californium preconcentrated from the alkaline matrix using an
iron/titanium hydroxide precipitation (enhanced with calcium phosphate precipitation) followed by a
lanthanum fluoride matrix removal step. The fluoride precipitate is dissolved with nitric-boric acid and
diluted in nitric acid and aluminum nitrate to yield a load solution containing ~3M HNO3-IM AI(NC>3)3.
Extraction chromatography resins (TEVA® + DGA® resins) are then used to isolate and purify californium
and americium by removing interfering radionuclides and other matrix components. Following chemical
separation of curium and americium, the sample test source is prepared by microprecipitation with cerium
(III) fluoride (CeFs).
Water: This method is capable of achieving a required method uncertainty for 252Cf of 2.0 picocuries/liter
(pCi/L) at an analytical action level of 15.3 pCi/L and a required minimum detectable concentration (MDC)
of 1.5 pCi/L. To attain these measurement quality objectives (MQOs), a sample volume of 0.2 L and
count time of at least 4 hours are recommended.
Air Particulate Filter. This method is capable of achieving a required method uncertainty for 252Cf of 0.57
pCi/filter at an analytical action level of 4.37 pCi/filter and a required MDC of 0.44 pCi/filter. To attain
these MQOs, a sample aliquant of one filter and count time of at least 4 hours are recommended.
U.S. Environmental Protection Agency
Office of Research and Development, Homeland Security Research Program
EPA/600/S-16/269
September 2016

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Swipe or Organic-Polymer-Based Air Particulate Filter. This method is capable of achieving a
required method uncertainty for 252Cf of 0.12 pCi/swipe or filter at an analytical action level of 0.12 pCi/
swipe or filter and a required MDC of 0.15 pCi/swipe or filter. To attain these MQOs, a sample aliquant of
one swipe or filter and count time of at least 4 hours are recommended.
Soil: This method is capable of achieving a required method uncertainty for252Cf of 0.18 pCi/gram (g) at
an analytical action level of 1.38 pCi/g and a required MDC of 0.14 pCi/g. To attain these MQOs, a
sample weight of 1 gram and count time of at least 4 hours are recommended.
Special Considerations: Alpha emissions from 250Cf fall in the same region as 252Cf and cannot be
differentiated from those of 252Cf using alpha spectrometric determinations. Alpha spectrometry
measurements should be reported in terms of the activity of 252/250Cf. Since alpha spectrometry
measurements does not differentiate between 250Cf and 252Cf, decay corrections based on the half-life of
252Cf will impart a positive bias to results as mixtures age. The effect can be minimized by keeping the
time between the activity reference date (i.e., collection or standard reference date) short, or, if
acceptable to the user of the data, by reporting the activity at the time of the measurement.
Radionuclides of other elements (or their short-lived progeny) that emit alpha particles that are
isoenergetic with 252Cf (e.g., Bismuth-212 at 6.1 mega-electron volts [MeV] supported by Thorium-228
and/or Radium-224) must be chemically separated to prevent positive interference with the measurement.
This method effectively separates these radionuclides.
DGA® has very high affinity for both Cf and Am. The retention of Cf on DGA, however, is higher than that
of Am. The use of the 243Am tracer for quantification assumes that both californium and americium are
quantitatively removed from the column at the time of elution. The separation scheme employed is
designed to ensure that two constituents, nitrates and lanthanum (La), will not interfere with this elution.
The dilute nitric acid rinse performed on DGA resin for soil samples is designed to remove calcium (Ca)
and La ions, which could end up on the final alpha source filter and coprecipitate with cerium fluoride.
Vacuum box lid and holes should be cleaned frequently to prevent cross-contamination of samples.
Non-radiological anions that can complex Cf and Am, including fluoride and phosphate, can lead to
depressed yields. Boric acid added to the load solution will complex residual fluoride ions, while aluminum
in the load solution will complex phosphate ions that could be present. High levels of Ca present in soil
samples could have an adverse impact on retention of californium and americium retention on DGA resin.
The method is designed to minimize Ca interference and enhance californium and americium affinity by
increasing the nitrate concentration in the load and initial rinse solutions.
Source: U.S. EPA National Air and Radiation Environmental Laboratory (NAREL). "Rapid Radiochemical
Method for Cf-252 in Water, Air Particulate Filters, Swipes and Soil." EPA 402-R16-002, Revision 0,
August 2016. https://www.epa.qov/radiation/rapid-radiochemical-methods-selected-radionuclides
U.S. Environmental Protection Agency
Office of Research and Development, Homeland Security Research Program
EPA/600/S-16/269
September 2016

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