ASTM C1255-93(1999)
(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
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.
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Designation: C 1255 – 93 (Reapproved 1999)
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 C 1255; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope D 1587 Practice for Thin-Walled Tube Sampling of Soils
D 2113 Practice for Diamond Core Drilling for Site Inves-
1.1 This test method covers the energy dispersive X-ray
tigation
fluorescence(EDXRF)spectrochemicalanalysisoftracelevels
D 3550 Practice for Ring-Lined Barrel Sampling of Soils
of uranium and thorium in soils.Any sample matrix that differs
D 4697 Guide for Maintaining Test Methods in the User’s
from the general ground soil composition used for calibration
Laboratory
(that is, fertilizer or a sample of mostly rock) would have to be
E 135 Terminology Relating to Analytical Chemistry for
calibrated separately to determine the effect of the different
Metals, Ores, and Related Materials
matrix composition.
E 305 Practice for Establishing and Controlling Spectro-
1.2 The analysis is performed after an initial drying and
chemical Analytical Curves
grinding of the sample, and the results are reported on a dry
E 456 Terminology Relating to Quality and Statistics
basis. The sample preparation technique used incorporates into
E 876 Practice for Use of Statistics in the Evaluation of
the sample any rocks and organic material present in the soil.
Spectrometric Data
This test method of sample preparation differs from other
E 882 Guide for Accountability and Quality Control in the
techniques that involve tumbling and sieving the sample.
Chemical Analysis Laboratory
1.3 Linear calibration is performed over a concentration
2.2 Other Document:
range from 20 to 1000 µg per gram for uranium and thorium.
NBS Radiation Safety Handbook Number 111 for X-Ray
1.4 The values stated in SI units are to be regarded as the
Diffraction and Fluorescence Analysis Equipment
standard. The inch-pound units in parentheses are for informa-
tion only.
3. Terminology
1.5 This standard does not purport to address all of the
3.1 Definitions:
safety concerns, if any, associated with its use. It is the
3.1.1 For definitions of terms relating to analytical atomic
responsibility of the user of this standard to establish appro-
spectroscopy, refer to Terminology E 135.
priate safety and health practices and determine the applica-
3.1.2 For definitions of terms relating to statistics refer to
bility of regulatory limitations prior to use.
Terminology E 456.
2. Referenced Documents 3.2 Definitions of Terms Specific to This Standard:
3.2.1 escape peak—a peak generated by an X-ray having
2.1 ASTM Standards:
energy greater than 1.84 keV (the energy of the k-alpha
C 982 Guide for Selecting Components for Energy Disper-
absorption edge for silicon) that enters the detector and causes
sive X-Ray Fluorescence (XRF) Systems
the silicon detector crystal to fluoresce. If the silicon X-ray
C 998 Practice for Sampling Surface Soil for Radionu-
escapes the detector, carrying with it the energy of the silicon
clides
k-alpha X-ray, 2.79 E-16 Joules [J] (1.74 keV), the energy
D 420 GuideforInvestigatingandSamplingSoilandRock
measured for the detected X-ray will be less than the actual
D 1452 Practice for Soil Investigation and Sampling by
X-ray energy by exactly 2.79 E-16 J (1.74 keV). Therefore, as
Auger Borings
counts accumulate for any major X-ray peak, an escape peak
D 1586 Test Method for Penetration Test and Split-Barrel
can be expected to appear at an energy of 2.79 E-16 J (1.74
Sampling of Soils
1 4
ThistestmethodisunderthejurisdictionofASTMCommitteeC-26onNuclear Annual Book of ASTM Standards, Vol 07.02.
Fuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods of Annual Book of ASTM Standards, Vol 03.05.
Tests. Annual Book of ASTM Standards, Vol 14.02.
Current edition approved Nov. 15, 1993. Published March 1994. Annual Book of ASTM Standards, Vol 03.06.
2 8
Annual Book of ASTM Standards, Vol 12.01. Available from the U.S. Department of Commerce, National Institute of
Annual Book of ASTM Standards, Vol 04.08. Standards and Technology, Gaithersburg, MD 20899.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C 1255
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 insrumentation 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
the X-ray energy flux.
7. Apparatus
7.1 Energy Dispersive X-Ray Fluorescence (EDXRF) Sys-
4. Summary of Test Method
tem, refer to Guide C 982.
4.1 A representative sample of soil is obtained by first
7.1.1 Photon Excitation Source, capable of producing
taking a sizeable amount (>100 g) and drying it, then running monochromatic X-rays of an appropriate energy to efficiently
it through a crusher and placing it on a shaker/tumbler to
excite uranium and thorium, that is, from 2.72 E-15 to 3.52
homogenize it. A portion is then ground in a ball mill and
E-15 Joules [J] (from 17 to 22 keV). Refer to Section 8 of
pressed into a sample pellet. An energy dispersive X-ray
Guide C 982. Either of the following sources is acceptable:
fluorescence spectrometer is used to expose the sample to a
7.1.1.1 Radioactive Source, 109-Cd is well suited for effi-
monochromatic X-ray source capable of exciting the uranium
cient excitation. It should have an activity between 2.59 E + 08
and thorium L-alpha series lines. The X-rays emitted by the
and 3.70 E + 08 becquerels (between 7 and 10 millicurie).
sample are detected via a solid state detector [Si(Li)] and
7.1.1.2 X-Ray Generator, with high voltage power supply,
counted in discrete energy channels on a multi-channel ana-
rhodium target X-ray tube and a secondary target; molybde-
lyzer(MCA)toformanenergyspectrum.Thespectrumisthen
num (Mo), rhodium (Rh) or silver (Ag) are suitable secondary
processed to obtain the peak intensities for uranium and
targets.
thorium for calibration and quantitation.
7.1.2 Solid State Detector [Si(Li)], with preamplifier main-
tained at liquid nitrogen temperature and capable of 2.64 E-17
5. Significance and Use
J (165 eV) FWHM resolution or better using an Fe-55
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-
tion of an on-site area to indicated points of contamination.
NOTE 1—Automatic correction for count rate losses due to pulse pileup
Then after cleanup, EDXRF may be used to verify the
or electronics deadtime is achieved in the pulse processing electronics (as
elimination of contamination or other analysis methods (such is available in most commercial X-ray units). Along with the automatic
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
segregation of soil lots by established contamination levels
adjusted for a given sample matrix and set of excitation conditions to
during on-site construction and excavation.
achieve a 50 % deadtime.
7.2 Drying Oven, controlled at 110 6 5° Celsius.
6. Interferences
7.3 Analytical Jaw Tooth Crusher, or equivalent, capable of
6.1 The following elements typically are found in an X-ray
crushing to 0.1 mm particle size.
spectrum from soil in the spectral region of uranium and
7.4 Laboratory Vacuum Cleaner, with a high efficiency
thorium: zinc (Zn), tungsten (W), lead (Pb), rubidium (Rb),
particulate air (HEPA) filter element.
strontium (Sr), and yttrium (Y).
6.2 Rubidium is the primary interference for uranium,
overlapping the uranium L-alpha-1 peak, and lead is the
primary interference for thorium, overlapping the thorium
The boldface numbers in parentheses refer to a list of references at the end of
L-alpha-1 peak. At typical levels for these elements all of the the text.
C 1255
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 C 982 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 below using the jaw tooth crusher may be used to homogenize
the soil and grind it to a particle size of U.S. Sieve 150 mesh with an
10. Sampling, Test Specimens, and Test Units
aperture of 106 µm.
10.1 Practice C 998 gives a practice for sampling of surface
soil to obtain a representative sa
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