ASTM C1255-18

Standard Test Method for Analysis of Uranium and Thorium in Soils by Energy Dispersive X-Ray Fluorescence Spectroscopy

SIGNIFICANCE AND USE
5.1 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 indicate 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 μg 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-May-2018
• ICS: 27.120.30 - Fissile materials and nuclear fuel technology
• Technical Committee: C26 - Nuclear Fuel Cycle
• Drafting Committee: C26.05 - Methods of Test

Relations

• Replaces: ASTM C1255-11 - Standard Test Method for Analysis of Uranium and Thorium in Soils by Energy Dispersive X-Ray Fluorescence Spectroscopy
• Effective Date: 01-Jun-2018
• Refers: ASTM C859-24 - Standard Terminology Relating to Nuclear Materials
• Effective Date: 01-Jan-2024
• Refers: ASTM E456-13a(2022)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Apr-2022
• Refers: ASTM E135-20 - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 01-Jan-2020
• Refers: ASTM E135-19 - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 15-May-2019
• Refers: ASTM D420-18 - Standard Guide for Site Characterization for Engineering Design and Construction Purposes
• Effective Date: 01-Feb-2018
• Refers: ASTM E456-13A(2017)e3 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017
• Refers: ASTM E456-13A(2017)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017
• Refers: ASTM C998-17 - Standard Practice for Sampling Surface Soil for Radionuclides
• Effective Date: 01-Jun-2017
• Refers: ASTM D3550/D3550M-17 - Standard Practice for Thick Wall, Ring-Lined, Split Barrel, Drive Sampling of Soils
• Effective Date: 01-Apr-2017
• Refers: ASTM E882-10(2016) - Standard Guide for Accountability and Quality Control in the Chemical Analysis Laboratory
• Effective Date: 01-Dec-2016
• Refers: ASTM E882-10(2016)e1 - Standard Guide for Accountability and Quality Control in the Chemical Analysis Laboratory
• Effective Date: 01-Dec-2016
• Refers: ASTM D1452/D1452M-16 - Standard Practice for Soil Exploration and Sampling by Auger Borings
• Effective Date: 01-Nov-2016
• Refers: ASTM E135-16 - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 15-May-2016
• Refers: ASTM D1587/D1587M-15 - Standard Practice for Thin-Walled Tube Sampling of Fine-Grained Soils for Geotechnical Purposes (Withdrawn 2024)
• Effective Date: 15-Nov-2015

Overview

ASTM C1255-18 is the international standard test method developed by ASTM International for the analysis of trace levels of uranium and thorium in soils using Energy Dispersive X-Ray Fluorescence Spectroscopy (EDXRF). This method is particularly significant in environmental monitoring, site assessment, and remediation at locations with potential radioactive contamination. By providing a robust procedure for quantifying uranium and thorium concentrations in soil, ASTM C1255-18 enables quick characterization and efficient verification of remediation efforts at contaminated sites.

The method involves drying and grinding soil samples, preparing pressed pellets, and analyzing them with EDXRF instrumentation. The test covers concentration ranges from 20 to 1000 μg/g and requires specific calibration and quality control measures to ensure accuracy and precision.

Key Topics

• Energy Dispersive X-Ray Fluorescence (EDXRF) Analysis: A non-destructive technique used for detecting and measuring uranium and thorium levels in soil samples.
• Sample Preparation: Includes drying, grinding, homogenization, and pelletizing the soil to incorporate rocks and organic matter. The results are reported on a dry weight basis.
• Calibration and Quality Control: Requires linear calibration with standards across the desired concentration range. Certified reference materials and blanks are used, and flux monitor ratios help correct for instrumental fluctuations.
• Detection Limits: The nominal detection limit is around 20 μg/g, suitable for identifying contamination close to natural background levels.
• Interferences and Corrections: The method uses mathematical deconvolution to handle spectral interferences from elements such as zinc, tungsten, lead, and rubidium.
• Safety Considerations: Involves handling ionizing radiation and fine particulates; therefore, strict adherence to health and safety practices is required.
• Instrumental Precision and Bias: Regular analysis of reference standards, blanks, and matrix-spiked samples helps ensure the reliability of results and identify any systematic errors or contamination during the process.

Applications

ASTM C1255-18 provides practical value in several fields:

• Environmental Site Assessment: Rapid screening of soil for uranium and thorium contamination at legacy nuclear sites, uranium mills, or areas impacted by radioactive materials.
• Remediation Verification: Post-cleanup verification to confirm effective removal of radioactive contaminants from soil, supporting regulatory compliance.
• Construction and Excavation: Segregation of soil lots on-site based on measured contamination levels, helping manage waste disposal and worker safety.
• Research and Monitoring: Used by laboratories and agencies involved in soil science, environmental monitoring, and studies on geochemical baselines of uranium and thorium.

EDXRF analysis, as outlined in this standard, allows for non-destructive, relatively rapid, and onsite assessment, making it well-suited for preliminary evaluations and ongoing monitoring of hazardous sites.

Related Standards

ASTM C1255-18 references and complements a number of other standards crucial to soil sampling, preparation, and analysis, including:

• ASTM C859 – Terminology Relating to Nuclear Materials
• ASTM C998 – Practice for Sampling Surface Soil for Radionuclides
• ASTM D420 – Guide for Site Characterization for Engineering Design and Construction
• ASTM D1452/D1452M – Practice for Soil Exploration and Sampling by Auger Borings
• ASTM D1586/D1586M, D1587/D1587M, D2113, and D3550/D3550M – Methods for various soil and rock sampling techniques
• ASTM E135 – Terminology Relating to Analytical Chemistry for Metals
• ANSI/HPS N43.2-2001 – Radiation Safety for X-ray Diffractometry and X-ray Fluorescence Equipment

For laboratories, consultants, and site managers, compliance with ASTM C1255-18 and related standards ensures reliable, accurate, and safe analysis of uranium and thorium in soils, supporting informed decision-making in environmental protection and remediation.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C1255 − 18
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.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 This test method covers the energy dispersive X-ray 2.1 ASTM Standards:
fluorescence(EDXRF)spectrochemicalanalysisoftracelevels C859Terminology Relating to Nuclear Materials
ofuraniumandthoriuminsoils.Anysamplematrixthatdiffers C998Practice for Sampling Surface Soil for Radionuclides
from the general ground soil composition used for calibration D420Guide for Site Characterization for Engineering De-
(thatis,fertilizerorasampleofmostlyrock)wouldhavetobe sign and Construction Purposes
calibrated separately to determine the effect of the different D1452/D1452MPractice for Soil Exploration and Sampling
matrix composition. by Auger Borings
D1586TestMethodforStandardPenetrationTest(SPT)and
1.2 The analysis is performed after an initial drying and
Split-Barrel Sampling of Soils
grinding of the sample, and the results are reported on a dry
D1587/D1587MPractice forThin-WalledTube Sampling of
basis.Thesamplepreparationtechniqueusedincorporatesinto
Fine-Grained Soils for Geotechnical Purposes
the sample any rocks and organic material present in the soil.
D2113Practice for Rock Core Drilling and Sampling of
This test method of sample preparation differs from other
Rock for Site Exploration
techniques that involve tumbling and sieving the sample.
D3550/D3550MPractice for Thick Wall, Ring-Lined, Split
1.3 Linear calibration is performed over a concentration
Barrel, Drive Sampling of Soils
range from 20 to 1000 µg per gram for uranium and thorium.
D4697Guide for Maintaining Test Methods in the User’s
Laboratory (Withdrawn 2009)
1.4 The values stated in SI units are to be regarded as the
standard.The inch-pound units in parentheses are for informa- E135Terminology Relating to Analytical Chemistry for
tion only. Metals, Ores, and Related Materials
E305Practice for Establishing and Controlling Atomic
1.5 This standard does not purport to address all of the
Emission Spectrochemical Analytical Curves
safety concerns, if any, associated with its use. It is the
E456Terminology Relating to Quality and Statistics
responsibility of the user of this standard to establish appro-
E876Practice for Use of Statistics in the Evaluation of
priate safety, health, and environmental practices and deter-
Spectrometric Data (Withdrawn 2003)
mine the applicability of regulatory limitations prior to use.
E882Guide for Accountability and Quality Control in the
1.6 This international standard was developed in accor-
Chemical Analysis Laboratory
dance with internationally recognized principles on standard-
2.2 Other Document:
ization established in the Decision on Principles for the
ANSI/HPS N43.2-2001Radiation Safety for X-ray Diffrac-
Development of International Standards, Guides and Recom-
tion and X-ray Fluorescence Equipment
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
ThistestmethodisunderthejurisdictionofASTMCommitteeC26onNuclear Standards volume information, refer to the standard’s Document Summary page on
Fuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods of the ASTM website.
Test. The last approved version of this historical standard is referenced on
CurrenteditionapprovedJune1,2018.PublishedJuly2018.Originallyapproved www.astm.org.
in 1993. Last previous edition approved in 2011 as C1255–11. DOI: 10.1520/ Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
C1255-18. 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1255 − 18
3. Terminology µg per gram) approaches typical background levels for these
contaminants, the method can be used as a quick characteriza-
3.1 Definitions:
tionofanon-siteareatoindicatepointsofcontamination.Then
3.1.1 For definitions of terms relating to the nuclear fuel
aftercleanup,EDXRFmaybeusedtoverifytheeliminationof
cycle, refer to Terminology C859.
contamination or other analysis methods (such as colorimetry,
3.1.2 For definitions of terms relating to analytical atomic
fluoremetry, phosphorescence, etc.) can be used if it is neces-
spectroscopy, refer to Terminology E135.
sary to test for cleanup down to a required background level.
3.1.3 For definitions of terms relating to statistics refer to
This test method can also be used for the segregation of soil
Terminology E456.
lots by established contamination levels during on-site con-
3.2 Definitions of Terms Specific to This Standard:
struction and excavation.
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
6. Interferences
absorption edge for silicon) that enters the detector and causes
the silicon detector crystal to fluoresce.
6.1 The following elements typically are found in an X-ray
3.2.1.1 Discussion—If the silicon X-ray escapes the spectrum from soil in the spectral region of uranium and
detector, carrying with it the energy of the silicon k-alpha
thorium: zinc (Zn), tungsten (W), lead (Pb), rubidium (Rb),
X-ray, 2.79 E-16 Joules [J] (1.74 keV), the energy measured
strontium (Sr), and yttrium (Y).
forthedetectedX-raywillbelessthantheactualX-rayenergy
6.2 Rubidium is the primary interference for uranium,
by exactly 2.79 E-16 J (1.74 keV). Therefore, as counts
overlapping the uranium L-alpha-1 peak, and lead is the
accumulate for any major X-ray peak, an escape peak can be
primary interference for thorium, overlapping the thorium
expected to appear at an energy of 2.79 E-16 J (1.74 keV)
L-alpha-1 peak. At typical levels for these elements all of the
below the major peak. Escape peaks can be calculated and
peak interferences can be eliminated by using a Gaussian
removed from the spectrum by most instrumentation software.
mathematical peak fitting and deconvolution software routine.
3.2.2 flux monitor (FM) value—the detected X-ray intensity
(Such is usually part of EDXRF instrumental software.)
within a specified spectral range from a metallic standard
However, if the lead level is high (greater than 500 µg per
giving a high number of counts.
gram), due, for instance, to the contamination of the soil by
3.2.2.1 Discussion—The same excitation conditions as the
lead paint, then the peak segregation can become impossible.
sample analysis are used (except for the change in the current
(Acomplete discussion of interelement effects and the correc-
toachievemaximumefficiencyofthedataacquisitionsystem).
tion models used to compensate for these effects is outside the
With all conditions remaining constant, the FM value is
scope of this procedure.) Explanations are found in several
proportional to the X-ray energy flux being emitted from the
sources (1, 2).
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.
(as is available with most instruments).
3.2.3.1 Discussion—This ratio is used to correct the mea-
sured element intensity for changes in the X-ray energy flux.
7. Apparatus
4. Summary of Test Method 7.1 Energy Dispersive X-Ray Fluorescence (EDXRF)
System, refer to manufacturer’s literature for the selection of
4.1 A representative sample of soil is obtained by first
the X-ray spectrometer.
taking a sizeable amount (>100 g) and drying it, then running
7.1.1 Photon Excitation Source, capable of producing
it through a crusher and placing it on a shaker/tumbler to
monochromatic X-rays of an appropriate energy to efficiently
homogenize it. A portion is then ground in a ball mill and
excite uranium and thorium, that is, from 2.72 E-15 to 3.52
pressed into a sample pellet. An energy dispersive X-ray
E-15 Joules [J] (from 17 to 22 keV). Either of the following
fluorescence spectrometer is used to expose the sample to a
sources is acceptable:
monochromatic X-ray source capable of exciting the uranium
7.1.1.1 Radioactive Source, Cdiswellsuitedforefficient
and thorium L-alpha series lines. The X-rays emitted by the
excitation. It should have an activity between 2.59 E+08 and
sample are detected via a solid state detector [Si(Li)] and
3.70 E+08 becquerels (between 7 and 10 millicurie).
counted in discrete energy channels on a multi-channel ana-
7.1.1.2 X-Ray Generator, with high voltage power supply,
lyzer(MCA)toformanenergyspectrum.Thespectrumisthen
rhodium target X-ray tube and a secondary target; molybde-
processed to obtain the peak intensities for uranium and
num (Mo), rhodium (Rh) or silver (Ag) are suitable secondary
thorium for calibration and quantitation.
targets.
5. Significance and Use
7.1.2 Solid State Detector [Si(Li)], with preamplifier main-
tained at appropriate temperature and capable of 2.64 E-17 J
5.1 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
The boldface numbers in parentheses refer to a list of references at the end of
soils. Since the detection limit of this technique (nominally 20 the text.
C1255 − 18
(165 eV) FWHM resolution or better using an Fe radioiso- tion of the X-ray beam by the user. Do NOT override these
tope source with 1000 cps intensity of the emitted Mn K-alpha interlocks without proper training or a second knowledgeable
peak at 9.453 E-16 J (5.900 keV). person present during sup operation. (See ANSI/HPS N43.2-
7.1.3 Signal Processing and Data Acquisition Electronics, 2001.)
includes: a bias power supply; a shaping amplifier or pulse
9.2 When cleaning out the grinder and sample mixing vials
processor using a 7.5 µs pulse shaping time constant; a pulse
with course sand or crushed glass, the resultant finely pow-
pileup rejector; an analog-to-digital converter (ADC); and
dered glass is a health hazard if inhaled; crystalline silica can
multi-channel scaler.
cause silicosis if exposure occurs on a regular basis. All such
NOTE1—Automaticcorrectionforcountratelossesduetopulsepileup
operations must be performed in a properly functioning ex-
or electronics deadtime is achieved in the pulse processing electronics (as
haust hood.
is available in most commercial X-ray units). Along with the automatic
count rate correction, the maximum efficiency of the data acquisition
10. Sampling, Test Specimens, and Test Units
system(thatis,thepreamplifier,pulseprocessor,andADC)isachievedat
a 50% deadtime count rate. This is based on an electronic analysis of
10.1 Practice C998 gives a practice for sampling of surface
counting losses by the manufacturer. The X-ray tube current is therefore
soil to obtain a representative sample for analysis of radionu-
adjusted for a given sample matrix and set of excitation conditions to
achieve a 50% deadtime. clides. Guide D420 provides a guide for investigating and
sampling soil and rock materials at subsurface levels but is
7.2 Drying Oven, controlled at 110 6 5° Celsius.
mainly concerned with geological characterization. The
7.3 Analytical Jaw Tooth Crusher, or equivalent, capable of
method described in Test Method D1587/D1587M may be
crushing to 0.1 mm particle size.
used to sample the soil using a thin-walled tube. If the soil is
7.4 Laboratory Vacuum Cleaner, with a high efficiency too hard for pushing, the tube may be driven or Practice
particulate air (HEPA) filter element.
D3550/D3550M may be used. The method described in Test
Method D1586 may also be used to sample the soil and
7.5 Shaker/Tumbler, capable of blending a large volume of
includes discussion on drilling procedures and collecting
dry soil (at least 100 g) in a sample container. The shaker/
samples which are representative of the area. In the case of
tumbler may have a capacity to blend several containers.
samplingrockyterrain,diamondcoredrillingmaybeused(see
7.6 Impact Grinding/Mixing Mill, capable of accepting the
Practice D2113). Where disturbed sampling techniques can be
vialin8.2.3.Anequivalentprocessmaybeusedtoachievethe
afforded, Practice D1452/D1452M can be used, that is, using
particle size specified in the sample preparation Section 11.
anAuger boring technique. The size of the sample is based on
achieving a representative sample. Tube samples can be
7.7 Hydraulic Press, 2.22 E+05 N (25 ton-force) load
capacity. composited to achieve such a sample. Refer to the standards
mentioned above that discuss obtaining a representative
7.8 Desiccator.
sample.
8. Reagents and Materials
11. Sample Preparation
8.1 Reagents—None.
11.1 As stated in the scope, the analysis is performed on a
8.2 Materials:
dry weight basis, however, the percent moisture of the soil
8.2.1 Evaporating Dishes, glazed porcelain, size No. 7 or
sample can be determined during the following steps by
larger, with a 2.00 E-4 m (200 mL) capacity.
measuring the weight before and after drying. This provides
8.2.2 Watch Glasses,sizeappropriatetocovertheevaporat-
the opportunity to calculate and report the data on an as-
ing dish.
received basis or the percent moisture can be reported sepa-
8.2.3 Grinding/Mixing Vial Set, with two mixing balls,
rately. Transfer the laboratory soil sample into an evaporating
made of steel or tungsten carbide, ball diameters of nominally
dish and cover the dish with a watch glass. Place the evapo-
13mm(0.5in.),withagrindingsamplecapacityof10cm .An
rating dish into a drying oven maintained at 105° Celsius.
equivalent process and set of materials may be used to achieve
Allow it to dry for a minimum of 18 h. Remove the dish from
the same particle size specified in the sample preparation
the oven and allow it to cool to room temperature.
section.
8.2.4 Die Press Set, 31 mm diameter with a maximum load
NOTE2—Itisrecommendedthatasamplepreparationlogbedeveloped
capacity in excess of 2.22 E+05 N (25 ton-force), or as
and implemented by the user which details and tracks the steps of
required for the instrument in use.
preparation for each sample. For each sample, the sample preparation log
would list: the jaw tooth crusher; mixing vial number; grinder/mixing
8.2.5 Retaining Cup, aluminum, 32 mm diameter, suitable
mill; and die press set used, as well as the preparer’s name, and the date
for the die press, or as required for the instrument in use.
and time of preparation. Such a log is useful in backtracking cross
contamination or sample carry over problems that are detected from the
9. Hazards
blank,standard,andcontrolsampledata(see13.2).Whenmultiplepieces
of equipment are used for any one of the processing steps, the equipment
9.1 XRF equipment analyzes by the interaction of ionizing
should be numbered and the vials and die sets should be scribed with
radiation with the sample. Applicable safety regulations and
numbers for tracking purposes.
standard operating procedures must be reviewed prior to the
use of such equipment. All modern XRF spectrometers are 11.2 A Geiger-Muller counter may be used to survey the
equipped with safety interlocks to prevent accidental penetra- dried soil as a means of segregating any with a high level of
C1255 − 18
for use in an EDXRF instrument in which the sample is inverted facing a
contamination. High activity level samples can then be pre-
lowermountedX-raytubeanddetector,aslongasthepelletissufficiently
pared on a separate jaw tooth crusher, if available, and the
thick to completely absorb the X-ray penetration.
cleaning process can be done twice to ensure against cross
11.10 Placethediepressonthehydraulicpressataforceof
contamination.
2.22 E+05 N (25 ton-force) for a minimum of 60 s, or as
NOTE3—Thecountrateusedtodenoteahighlevelsamplewilldepend
required for the instrument in use. Then remove the pressed
on the model of instrument used and its counting efficiency.
sample from the die. Mark the sample inside diameter (ID) on
11.3 Adjusttheparticlesizesettingonthejawtoothcrusher
thebackofthealuminumcapandhandlethesamplescarefully
to 0.1 mm.
so as not to abrade or disturb the surface.
NOTE 4—It is recommended that all crushing, tumbling, and mixing be
11.11 Wipe out any remaining powder residue from the die
performedinaproperlyfunctioninglaboratoryhood.Followthevendor’s
with a wetted paper towel.
instructions on the use of the jaw tooth crusher, shaker/tumbler, and the
impact grinding/mixing mill devices. An equivalent process to the one
12. Preparation of Apparatus
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
12.1 The X-ray spectrometer must be allowed to reach the
aperture of 106 µm.
level of stability as specified by the manufacturer’s instruc-
11.4 Priortotheinitialuseandaftereachconsecutiveuseof
tions.
the jaw tooth crusher, clean it out by running about 150 g of
12.2 The detector supply of liquid nitrogen (if required)
course sand through it. Then use a laboratory HEPA vacuum
must be maintained.
cleanertovacuumoutallresidualsandfromthecollectiontray,
12.3 Typical operating conditions are given in Table 1.
sample insertion region, etc.
Theseconditionsareinstrumentdependent;themanufacturer’s
11.5 Remove each sample from the evaporating dish and
guidelines should be followed.
runitthroughthejawtoothcrusher,cleaningasdirectedabove
after each use. Collect the sample in a sample container
13. Calibration and Standardization
suitable for tumbling, such as an 8 oz jar or disposable
13.1 Apparatus:
polyethylene container. The container must be less than three-
13.1.1 Peak Energy Calibration—Calibrate the gain and
fourths full to allow for adequate mixing in the tumbling
offset on the pulse processor to ensure proper peak position
process.
according to manufacturer’s instructions.
11.6 Place the sample on a shaker/tumbler for an appropri-
13.1.2 X-Ray Energy Flux Monitoring—Beforeacalibration
ate amount of time to allow for complete mixing. Consult the
is determined a factor, called the flux monitor ratio (FMR), is
manufacturer’s instructions to establish an appropriate mixing
establishedtoadjustforchangesintheX-raytubeoutputorthe
time.
X-ray energy flux. Refer to the terminol
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C1255 − 11 C1255 − 18
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
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 μg 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
C859 Terminology Relating to Nuclear Materials
C998 Practice for Sampling Surface Soil for Radionuclides
D420 Guide for Site Characterization for Engineering Design and Construction Purposes
D1452D1452/D1452M Practice for Soil Exploration and Sampling by Auger Borings
D1586 Test Method for Standard Penetration Test (SPT) and Split-Barrel Sampling of Soils
D1587D1587/D1587M Practice for Thin-Walled Tube Sampling of Fine-Grained Soils for Geotechnical Purposes
D2113 Practice for Rock Core Drilling and Sampling of Rock for Site Exploration
D3550D3550/D3550M Practice for Thick Wall, Ring-Lined, Split Barrel, Drive Sampling of Soils
D4697 Guide for Maintaining Test Methods in the User’s Laboratory (Withdrawn 2009)
E135 Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
E305 Practice for Establishing and Controlling Atomic Emission Spectrochemical Analytical Curves
E456 Terminology Relating to Quality and Statistics
E876 Practice for Use of Statistics in the Evaluation of Spectrometric Data (Withdrawn 2003)
E882 Guide for Accountability and Quality Control in the Chemical Analysis Laboratory
2.2 Other Document:
ANSI/HPS N43.2-2001 Radiation Safety for X-ray Diffraction and X-ray Fluorescence Equipment
This test method is under the jurisdiction of ASTM Committee C26 on Nuclear Fuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods of Test.
Current edition approved June 1, 2011June 1, 2018. Published June 2011July 2018. Originally approved in 1993. Last previous edition approved in 20052011 as
C1255 – 93 (2005).C1255 – 11. DOI: 10.1520/C1255-11.10.1520/C1255-18.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms relating to the nuclear fuel cycle, refer to Terminology C859.
3.1.2 For definitions of terms relating to analytical atomic spectroscopy, refer to Terminology E135.
3.1.3 For definitions of terms relating to statistics refer to Terminology E456.
3.2 Definitions of Terms Specific to This Standard:
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 absorption
edge for silicon) that enters the detector and causes the silicon detector crystal to fluoresce. If the silicon X-ray escapes the detector,
carrying with it the energy of the silicon k-alpha X-ray, 2.79 E-16 Joules [J] (1.74 keV), the energy measured for the detected X-ray
will be less than the actual X-ray energy by exactly 2.79 E-16 J (1.74 keV). Therefore, as counts accumulate for any major X-ray
peak, an escape peak can be expected to appear at an energy of 2.79 E-16 J (1.74 keV) below the major peak. Escape peaks can
be calculated and removed from the spectrum by most instrumentation software.
3.2.1.1 Discussion—
If the silicon X-ray escapes the detector, carrying with it the energy of the silicon k-alpha X-ray, 2.79 E-16 Joules [J] (1.74 keV),
the energy measured for the detected X-ray will be less than the actual X-ray energy by exactly 2.79 E-16 J (1.74 keV). Therefore,
as counts accumulate for any major X-ray peak, an escape peak can be expected to appear at an energy of 2.79 E-16 J (1.74 keV)
below the major peak. Escape peaks can be calculated and removed from the spectrum by most instrumentation software.
3.2.2 flux monitor (FM) value—the detected X-ray intensity within a specified spectral range from a metallic standard giving
a high number of counts. The same excitation conditions as the sample analysis are used (except for the change in the current to
achieve maximum efficiency of the data acquisition system). With all conditions remaining constant, the FM value is proportional
to the X-ray energy flux being emitted from the X-ray tube or radioisotope source.
3.2.2.1 Discussion—
The same excitation conditions as the sample analysis are used (except for the change in the current to achieve maximum efficiency
of the data acquisition system). With all conditions remaining constant, the FM value is proportional to the X-ray energy flux being
emitted from the X-ray tube or radioisotope source.
3.2.3 flux monitor ratio (FMR)—the ratio of the initial FM value (FMi) prior to calibration and sample analysis to current FM
value (FMc) at the time of sample analysis. This ratio is used to correct the measured element intensity for changes in the X-ray
energy flux.
3.2.3.1 Discussion—
This ratio is used to correct the measured element intensity for changes in the X-ray energy flux.
4. Summary of Test Method
4.1 A representative sample of soil is obtained by first taking a sizeable amount (>100 g) and drying it, then running it through
a crusher and placing it on a shaker/tumbler to homogenize it. A portion is then ground in a ball mill and pressed into a sample
pellet. An energy dispersive X-ray fluorescence spectrometer is used to expose the sample to a monochromatic X-ray source
capable of exciting the uranium and thorium L-alpha series lines. The X-rays emitted by the sample are detected via a solid state
detector [Si(Li)] and counted in discrete energy channels on a multi-channel analyzer (MCA) to form an energy spectrum. The
spectrum is then processed to obtain the peak intensities for uranium and thorium for calibration and quantitation.
5. Significance and Use
5.1 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 indicate 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.
6. Interferences
6.1 The following elements typically are found in an X-ray spectrum from soil in the spectral region of uranium and thorium:
zinc (Zn), tungsten (W), lead (Pb), rubidium (Rb), strontium (Sr), and yttrium (Y).
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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 L-alpha-1 peak. At typical levels for these elements all of the peak interferences
can be eliminated by using a Gaussian mathematical peak fitting and deconvolution software routine. (Such is usually part of
EDXRF instrumental software.) However, if the lead level is high (greater than 500 μg per gram), due, for instance, to the
contamination of the soil by lead paint, then the peak segregation can become impossible. (A complete discussion of interelement
effects and the correction models used to compensate for these effects is outside the scope of this procedure.) Explanations are
found in several sources (1, 2).
6.3 Escape peaks (see 3.2.1) can interfere with the integration of the uranium and thorium L-alpha peaks and are therefore
removed from the spectrum with a software operation (as is available with most instruments).
7. Apparatus
7.1 Energy Dispersive X-Ray Fluorescence (EDXRF) System, refer to manufacturer’s literature for the selection of the X-ray
spectrometer.
7.1.1 Photon Excitation Source, capable of producing monochromatic X-rays of an appropriate energy to efficiently excite
uranium and thorium, that is, from 2.72 E-15 to 3.52 E-15 Joules [J] (from 17 to 22 keV). Either of the following sources is
acceptable:
7.1.1.1 Radioactive Source, Cd is well suited for efficient excitation. It should have an activity between 2.59 E + 08 and 3.70
E + 08 becquerels (between 7 and 10 millicurie).
7.1.1.2 X-Ray Generator, with high voltage power supply, rhodium target X-ray tube and a secondary target; molybdenum (Mo),
rhodium (Rh) or silver (Ag) are suitable secondary targets.
7.1.2 Solid State Detector [Si(Li)], with preamplifier maintained at liquid nitrogen appropriate temperature and capable of 2.64
E-17 J (165 eV) FWHM resolution or better using an Fe radioisotope source with 1000 cps intensity of the emitted Mn K-alpha
peak at 9.453 E-16 J (5.900 keV).
7.1.3 Signal Processing and Data Acquisition Electronics, includes: a bias power supply; a shaping amplifier or pulse processor
using a 7.5 μs pulse shaping time constant; a pulse pileup rejector; an analog-to-digital converter (ADC); and multi-channel scaler.
NOTE 1—Automatic correction for count rate losses due to pulse pileup or electronics deadtime is achieved in the pulse processing electronics (as is
available in most commercial X-ray units). Along with the automatic count rate correction, the maximum efficiency of the data acquisition system (that
is, the preamplifier, pulse processor, and ADC) is achieved at a 50 % deadtime count rate. This is based on an electronic analysis of counting losses by
the manufacturer. The X-ray tube current is therefore adjusted for a given sample matrix and set of excitation conditions to achieve a 50 % deadtime.
7.2 Drying Oven, controlled at 110 6 5° Celsius.
7.3 Analytical Jaw Tooth Crusher, or equivalent, capable of crushing to 0.1 mm particle size.
7.4 Laboratory Vacuum Cleaner, with a high efficiency particulate air (HEPA) filter element.
7.5 Shaker/Tumbler, capable of blending a large volume of dry soil (at least 100 g) in a sample container. The shaker/tumbler
may have a capacity to blend several containers.
7.6 Impact Grinding/Mixing Mill, capable of accepting the vial in 8.2.3. An equivalent process may be used to achieve the
particle size specified in the sample preparation Section 11.
7.7 Hydraulic Press, 2.22 E + 05 N (25 ton-force) load capacity.
7.8 Desiccator.
8. Reagents and Materials
8.1 Reagents—None.
8.2 Materials:
8.2.1 Evaporating Dishes, glazed porcelain, size No. 7 or larger, with a 2.00 E-4 m (200 mL) capacity.
8.2.2 Watch Glasses, size appropriate to cover the evaporating dish.
8.2.3 Grinding/Mixing Vial Set, with two mixing balls, made of steel or tungsten carbide, ball diameters of nominally 13 mm
(0.5 in.), with a grinding sample capacity of 10 cm . An equivalent process and set of materials may be used to achieve the same
particle size specified in the sample preparation section.
8.2.4 Die Press Set, 31 mm diameter with a maximum load capacity in excess of 2.22 E + 05 N (25 ton-force).ton-force), or
as required for the instrument in use.
8.2.5 Retaining Cup, aluminum, 32 mm diameter, suitable for the die press.press, or as required for the instrument in use.
9. Hazards
9.1 XRF equipment analyzes by the interaction of ionizing radiation with the sample. Applicable safety regulations and standard
operating procedures must be reviewed prior to the use of such equipment. All modern XRF spectrometers are equipped with safety
The boldface numbers in parentheses refer to a list of references at the end of the text.
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interlocks to prevent accidental penetration of the X-ray beam by the user. Do NOT override these interlocks without proper
training or a second knowledgeable person present during sup operation. (See ANSI/HPS N43.2-2001.)
9.2 When cleaning out the grinder and sample mixing vials with course sand or crushed glass, the resultant finely powdered
glass is a health hazard if inhaled; crystalline silica can cause silicosis if exposure occurs on a regular basis. All such operations
must be performed in a properly functioning exhaust hood.
10. Sampling, Test Specimens, and Test Units
10.1 Practice C998 gives a practice for sampling of surface soil to obtain a representative sample for analysis of radionuclides.
Guide D420 provides a guide for investigating and sampling soil and rock materials at subsurface levels but is mainly concerned
with geological characterization. The method described in Test Method D1587D1587/D1587M may be used to sample the soil
using a thin-walled tube. If the soil is too hard for pushing, the tube may be driven or Practice D3550D3550/D3550M may be used.
The method described in Test Method D1586 may also be used to sample the soil and includes discussion on drilling procedures
and collecting samples which are representative of the area. In the case of sampling rocky terrain, diamond core drilling may be
used (see Practice D2113). Where disturbed sampling techniques can be afforded, Practice D1452D1452/D1452M can be used, that
is, using an Auger boring technique. The size of the sample is based on achieving a representative sample. Tube samples can be
composited to achieve such a sample. Refer to the standards mentioned above that discuss obtaining a representative sample.
11. Sample Preparation
11.1 As stated in the scope, the analysis is performed on a dry weight basis, however, the percent moisture of the soil sample
can be determined during the following steps by measuring the weight before and after drying. This provides the opportunity to
calculate and report the data on an as-received basis or the percent moisture can be reported separately. Transfer the laboratory soil
sample into an evaporating dish and cover the dish with a watch glass. Place the evaporating dish into a drying oven maintained
at 105° Celsius. Allow it to dry for a minimum of 18 h. Remove the dish from the oven and allow it to cool to room temperature.
NOTE 2—It is recommended that a sample preparation log be developed and implemented by the user which details and tracks the steps of preparation
for each sample. For each sample, the sample preparation log would list: the jaw tooth crusher; mixing vial number; grinder/mixing mill; and die press
set used, as well as the preparer’s name, and the date and time of preparation. Such a log is useful in backtracking cross contamination or sample carry
over problems that are detected from the blank, standard, and control sample data (see 13.2). When multiple pieces of equipment are used for any one
of the processing steps, the equipment should be numbered and the vials and die sets should be scribed with numbers for tracking purposes.
11.2 A Geiger-Muller counter may be used to survey the dried soil as a means of segregating any with a high level of
contamination. High activity level samples can then be prepared on a separate jaw tooth crusher, if available, and the cleaning
process can be done twice to ensure against cross contamination.
NOTE 3—The count rate used to denote a high level sample will depend on the model of instrument used and its counting efficiency.
11.3 Adjust the particle size setting on the jaw tooth crusher to 0.1 mm.
NOTE 4—It is recommended that all crushing, tumbling, and mixing be performed in a properly functioning laboratory hood. Follow the vendor’s
instructions on the use of the jaw tooth crusher, shaker/tumbler, and the impact grinding/mixing mill devices. An equivalent process to the one 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 aperture of 106
μm.
11.4 Prior to the initial use and after each consecutive use of the jaw tooth crusher, clean it out by running about 150 g of course
sand through it. Then use a laboratory HEPA vacuum cleaner to vacuum out all residual sand from the collection tray, sample
insertion region, etc.
11.5 Remove each sample from the evaporating dish and run it through the jaw tooth crusher, cleaning as directed above after
each use. Collect the sample in a sample container suitable for tumbling, such as an 8 oz jar or disposable polyethylene container.
The container must be less than three-fourths full to allow for adequate mixing in the tumbling process.
11.6 Place the sample on a shaker/tumbler for an appropriate amount of time to allow for complete mixing. Consult the
manufacturer’s instructions to establish an appropriate mixing time.
11.7 Place approximately 15 cm of sample into a mixing vial with two mixing balls and place the vial inside the
grinding/mixing mill. Grind the sample for approximately 1500 s (25 min). An appropriate amount of time can be established from
a series of test samples (3, 4) taken from a single homogenous sample with concentrations near the mid-range. The test samples
would be prepared at incrementally longer grinding times and then analyzed. The appropriate grinding time would be at the point
in which any further increase in grinding time does not result in an appreciable increase in X-ray peak intensity.
11.8 The mixing vials are cleaned out after each use as follows:
11.8.1 Disassemble and rinse the vial components with water.
11.8.2 Blow or air dry the components and then reassemble the vial.
11.8.3 Place course ground glass or sand in the vial and run it on the grinding/mixing mill.
11.8.4 Remove the glass from the vial and wipe or blow out
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