ASTM C1255-93(2005)
(Test Method)Standard Test Method for Analysis of Uranium and Thorium in Soils by Energy Dispersive X-Ray Fluorescence Spectroscopy
Standard Test Method for Analysis of Uranium and Thorium in Soils by Energy Dispersive X-Ray Fluorescence Spectroscopy
SIGNIFICANCE AND USE
This test method was developed and the instrument calibrated using ground soils from the site of a nuclear materials plant. This test method can be used to measure the extent of contamination from uranium and thorium in ground soils. Since the detection limit of this technique (nominally 20 μg per gram) approaches typical background levels for these contaminants, the method can be used as a quick characterization of an on-site area to indicated points of contamination. Then after cleanup, EDXRF may be used to verify the elimination of contamination or other analysis methods (such as colorimetry, fluoremetry, phosphorescence, etc.) can be used if it is necessary to test for cleanup down to a required background level. This test method can also be used for the segregation of soil lots by established contamination levels during on-site construction and excavation.
SCOPE
1.1 This test method covers the energy dispersive X-ray fluorescence (EDXRF) spectrochemical analysis of trace levels of uranium and thorium in soils. Any sample matrix that differs from the general ground soil composition used for calibration (that is, fertilizer or a sample of mostly rock) would have to be calibrated separately to determine the effect of the different matrix composition.
1.2 The analysis is performed after an initial drying and grinding of the sample, and the results are reported on a dry basis. The sample preparation technique used incorporates into the sample any rocks and organic material present in the soil. This test method of sample preparation differs from other techniques that involve tumbling and sieving the sample.
1.3 Linear calibration is performed over a concentration range from 20 to 1000 [mu]g per gram for uranium and thorium.
1.4 The values stated in SI units are to be regarded as the standard. The inch-pound units in parentheses are for information only.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: C1255 – 93 (Reapproved 2005)
Standard Test Method for
Analysis of Uranium and Thorium in Soils by Energy
Dispersive X-Ray Fluorescence Spectroscopy
This standard is issued under the fixed designation C1255; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope D1452 PracticeforSoilExplorationandSamplingbyAuger
Borings
1.1 This test method covers the energy dispersive X-ray
D1586 Test Method for Penetration Test (SPT) and Split-
fluorescence(EDXRF)spectrochemicalanalysisoftracelevels
Barrel Sampling of Soils
ofuraniumandthoriuminsoils.Anysamplematrixthatdiffers
D1587 Practice forThin-WalledTube Sampling of Soils for
from the general ground soil composition used for calibration
Geotechnical Purposes
(that is, fertilizer or a sample of mostly rock) would have to be
D2113 Practice for Rock Core Drilling and Sampling of
calibrated separately to determine the effect of the different
Rock for Site Investigation
matrix composition.
D3550 Practice for Thick Wall, Ring-Lined, Split Barrel,
1.2 The analysis is performed after an initial drying and
Drive Sampling of Soils
grinding of the sample, and the results are reported on a dry
D4697 Guide for Maintaining Test Methods in the User’s
basis.The sample preparation technique used incorporates into
Laboratory
the sample any rocks and organic material present in the soil.
E135 Terminology Relating to Analytical Chemistry for
This test method of sample preparation differs from other
Metals, Ores, and Related Materials
techniques that involve tumbling and sieving the sample.
E305 Practice for Establishing and Controlling Atomic
1.3 Linear calibration is performed over a concentration
Emission Spectrochemical Analytical Curves
range from 20 to 1000 µg per gram for uranium and thorium.
E456 Terminology Relating to Quality and Statistics
1.4 The values stated in SI units are to be regarded as the
E876 Practice for Use of Statistics in the Evaluation of
standard. The inch-pound units in parentheses are for informa-
Spectrometric Data
tion only.
E882 Guide for Accountability and Quality Control in the
1.5 This standard does not purport to address all of the
Chemical Analysis Laboratory
safety concerns, if any, associated with its use. It is the
2.2 Other Document:
responsibility of the user of this standard to establish appro-
NBS Radiation Safety Handbook Number 111 for X-Ray
priate safety and health practices and determine the applica-
Diffraction and Fluorescence Analysis Equipment
bility of regulatory limitations prior to use.
3. Terminology
2. Referenced Documents
3.1 Definitions:
2.1 ASTM Standards:
3.1.1 For definitions of terms relating to analytical atomic
C982 Guide for Selecting Components for Energy-
spectroscopy, refer to Terminology E135.
Dispersive X-Ray Fluorescence (XRF) Systems
3.1.2 For definitions of terms relating to statistics refer to
C998 Practice for Sampling Surface Soil for Radionuclides
Terminology E456.
D420 Guide to Site Characterization for Engineering De-
3.2 Definitions of Terms Specific to This Standard:
sign and Construction Purposes
3.2.1 escape peak—a peak generated by an X-ray having
energy greater than 1.84 keV (the energy of the k-alpha
This test method is under the jurisdiction ofASTM Committee C26 on Nuclear absorption edge for silicon) that enters the detector and causes
Fuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods of
the silicon detector crystal to fluoresce. If the silicon X-ray
Test.
escapes the detector, carrying with it the energy of the silicon
Current edition approved June 1, 2005. Published December 2005. Originally
k-alpha X-ray, 2.79 E-16 Joules [J] (1.74 keV), the energy
approved in 1993. Last previous edition approved in 1999 as C1255 – 93 (1999).
DOI: 10.1520/C1255-93R05.
measured for the detected X-ray will be less than the actual
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
X-ray energy by exactly 2.79 E-16 J (1.74 keV). Therefore, as
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
3 4
Withdrawn. The last approved version of this historical standard is referenced Available from the U.S. Department of Commerce, National Institute of
on www.astm.org. Standards and Technology, Gaithersburg, MD 20899.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C1255 – 93 (2005)
counts accumulate for any major X-ray peak, an escape peak primary interference for thorium, overlapping the thorium
can be expected to appear at an energy of 2.79 E-16 J (1.74 L-alpha-1 peak. At typical levels for these elements all of the
keV) below the major peak. Escape peaks can be calculated peak interferences can be eliminated by using a Gaussian
and removed from the spectrum by most instrumentation mathematical peak fitting and deconvolution software routine.
software. (Such is usually part of EDXRF instrumental software.)
3.2.2 flux monitor (FM) value—the detected X-ray intensity However, if the lead level is high (greater than 500 µg per
within a specified spectral range from a metallic standard gram), due, for instance, to the contamination of the soil by
giving a high number of counts. The same excitation condi- lead paint, then the peak segregation can become impossible.
tions as the sample analysis are used (except for the change in (A complete discussion of interelement effects and the correc-
the current to achieve maximum efficiency of the data acqui- tion models used to compensate for these effects is outside the
sition system). With all conditions remaining constant, the FM scope of this procedure.) Explanations are found in several
value is proportional to the X-ray energy flux being emitted sources (1, 2).
from the X-ray tube or radioisotope source. 6.3 Escape peaks (see 3.2.1) can interfere with the integra-
3.2.3 flux monitor ratio (FMR)—the ratio of the initial FM tion of the uranium and thorium L-alpha peaks and are
value (FMi) prior to calibration and sample analysis to current thereforeremovedfromthespectrumwithasoftwareoperation
FM value (FMc) at the time of sample analysis. This ratio is (as is available with most instruments).
used to correct the measured element intensity for changes in
7. Apparatus
the X-ray energy flux.
7.1 Energy Dispersive X-Ray Fluorescence (EDXRF) Sys-
tem, refer to Guide C982.
4. Summary of Test Method
7.1.1 Photon Excitation Source, capable of producing
4.1 A representative sample of soil is obtained by first
monochromatic X-rays of an appropriate energy to efficiently
taking a sizeable amount (>100 g) and drying it, then running
excite uranium and thorium, that is, from 2.72 E-15 to 3.52
it through a crusher and placing it on a shaker/tumbler to
E-15 Joules [J] (from 17 to 22 keV). Refer to Section 8 of
homogenize it. A portion is then ground in a ball mill and
Guide C982. Either of the following sources is acceptable:
pressed into a sample pellet. An energy dispersive X-ray
7.1.1.1 Radioactive Source, 109-Cd is well suited for effi-
fluorescence spectrometer is used to expose the sample to a
cient excitation. It should have an activity between 2.59 E + 08
monochromatic X-ray source capable of exciting the uranium
and 3.70 E + 08 becquerels (between 7 and 10 millicurie).
and thorium L-alpha series lines. The X-rays emitted by the
7.1.1.2 X-Ray Generator, with high voltage power supply,
sample are detected via a solid state detector [Si(Li)] and
rhodium target X-ray tube and a secondary target; molybde-
counted in discrete energy channels on a multi-channel ana-
num (Mo), rhodium (Rh) or silver (Ag) are suitable secondary
lyzer(MCA)toformanenergyspectrum.Thespectrumisthen
targets.
processed to obtain the peak intensities for uranium and
7.1.2 Solid State Detector [Si(Li)], with preamplifier main-
thorium for calibration and quantitation.
tained at liquid nitrogen temperature and capable of 2.64 E-17
J (165 eV) FWHM resolution or better using an Fe-55
5. Significance and Use
radioisotope source with 1000 cps intensity of the emitted Mn
5.1 This test method was developed and the instrument
K-alpha peak at 9.453 E-16 J (5.900 keV).
calibrated using ground soils from the site of a nuclear
7.1.3 Signal Processing and Data Acquisition Electronics,
materials plant. This test method can be used to measure the
includes: a bias power supply; a shaping amplifier or pulse
extent of contamination from uranium and thorium in ground
processor using a 7.5 µs pulse shaping time constant; a pulse
soils. Since the detection limit of this technique (nominally 20
pileup rejector; an analog-to-digital converter (ADC); and
µg per gram) approaches typical background levels for these
multi-channel scaler.
contaminants, the method can be used as a quick characteriza-
NOTE 1—Automatic correction for count rate losses due to pulse pileup
tion of an on-site area to indicated points of contamination.
or electronics deadtime is achieved in the pulse processing electronics (as
Then after cleanup, EDXRF may be used to verify the
is available in most commercial X-ray units). Along with the automatic
elimination of contamination or other analysis methods (such
count rate correction, the maximum efficiency of the data acquisition
ascolorimetry,fluoremetry,phosphorescence,etc.)canbeused
system (that is, the preamplifier, pulse processor, andADC) is achieved at
if it is necessary to test for cleanup down to a required
a 50 % deadtime count rate. This is based on an electronic analysis of
background level. This test method can also be used for the counting losses by the manufacturer. The X-ray tube current is therefore
adjusted for a given sample matrix and set of excitation conditions to
segregation of soil lots by established contamination levels
achieve a 50 % deadtime.
during on-site construction and excavation.
7.2 Drying Oven, controlled at 110 6 5° Celsius.
6. Interferences
7.3 Analytical Jaw Tooth Crusher, or equivalent, capable of
crushing to 0.1 mm particle size.
6.1 The following elements typically are found in an X-ray
7.4 Laboratory Vacuum Cleaner, with a high efficiency
spectrum from soil in the spectral region of uranium and
particulate air (HEPA) filter element.
thorium: zinc (Zn), tungsten (W), lead (Pb), rubidium (Rb),
strontium (Sr), and yttrium (Y).
6.2 Rubidium is the primary interference for uranium,
The boldface numbers in parentheses refer to a list of references at the end of
overlapping the uranium L-alpha-1 peak, and lead is the the text.
C1255 – 93 (2005)
7.5 Shaker/Tumbler, capable of blending a large volume of 11. Sample Preparation
dry soil (at least 100 g) in a sample container. The shaker/
11.1 As stated in the scope, the analysis is performed on a
tumbler may have a capacity to blend several containers.
dry weight basis, however, the percent moisture of the soil
7.6 Impact Grinding/Mixing Mill, capable of accepting the
sample can be determined during the following steps by
vial in 8.2.3.An equivalent process may be used to achieve the
measuring the weight before and after drying. This provides
particle size specified in the sample preparation Section 11.
the opportunity to calculate and report the data on an as-
7.7 Hydraulic Press, 2.22 E + 05 N (25 ton-force) load
received basis or the percent moisture can be reported sepa-
capacity.
rately. Transfer the laboratory soil sample into an evaporating
7.8 Desiccator.
dish and cover the dish with a watch glass. Place the evapo-
rating dish into a drying oven maintained at 105° Celsius.
8. Reagents and Materials
Allow it to dry for a minimum of 18 h. Remove the dish from
8.1 Reagents—None.
the oven and allow it to cool to room temperature.
8.2 Materials:
NOTE 2—Itisrecommendedthatasamplepreparationlogbedeveloped
8.2.1 Evaporating Dishes, glazed porcelain, size No. 7 or
3 and implemented by the user which details and tracks the steps of
larger, with a 2.00 E-4 m (200 mL) capacity.
preparation for each sample. For each sample, the sample preparation log
8.2.2 Watch Glasses, size appropriate to cover the evaporat-
would list: the jaw tooth crusher; mixing vial number; grinder/mixing
ing dish.
mill; and die press set used, as well as the preparer’s name, and the date
8.2.3 Grinding/Mixing Vial Set, with two mixing balls,
and time of preparation. Such a log is useful in backtracking cross
made of steel or tungsten carbide, ball diameters of nominally contamination or sample carry over problems that are detected from the
blank, standard, and control sample data (see 13.2). When multiple pieces
13mm(0.5in.),withagrindingsamplecapacityof10cm .An
of equipment are used for any one of the processing steps, the equipment
equivalent process and set of materials may be used to achieve
should be numbered and the vials and die sets should be scribed with
the same particle size specified in the sample preparation
numbers for tracking purposes.
section.
11.2 A Geiger-Muller counter may be used to survey the
8.2.4 Die Press Set, 31 mm diameter with a maximum load
dried soil as a means of segregating any with a high level of
capacity in excess of 2.22 E + 05 N (25 ton-force).
contamination. High activity level samples can then be pre-
8.2.5 Retaining Cup, aluminum, 32 mm diameter, suitable
pared on a separate jaw tooth crusher, if available, and the
for the die press.
cleaning process can be done twice to ensure against cross
9. Hazards
contamination.
9.1 Refer to NBS Radiation Safety Handbook Number 111
NOTE 3—The count rate used to denote a high level sample will depend
and the Hazard Section of Guide C982 for the hazards
on the model of instrument used and its counting efficiency.
associated with the use of X-ray equipment.
11.3 Adjust the particle size setting on the jaw tooth crusher
9.2 When cleaning out the grinder and sample mixing vials
to 0.1 mm.
with course sand or crushed glass, the resultant finely pow-
dered glass is a health hazard if inhaled; crystalline silica can
NOTE 4—It is recommended that all crushing, tumbling, and mixing be
cause silicosis if exposure occurs on a regular basis. All such
performed in a properly functioning laboratory hood. Follow the vendor’s
operations must be performed in a properly functioning ex- instructions on the use of the jaw tooth crusher, shaker/tumbler, and the
impact grinding/mixing mill devices. An equivalent process to the one
haust hood.
described
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