1、Designation: C1255 18Standard Test Method forAnalysis of Uranium and Thorium in Soils by EnergyDispersive X-Ray Fluorescence Spectroscopy1This standard is issued under the fixed designation C1255; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、 of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the energy dispersive X-rayfluorescence (EDXRF) spectrochemical anal
3、ysis of trace levelsof uranium and thorium in soils.Any sample matrix that differsfrom the general ground soil composition used for calibration(that is, fertilizer or a sample of mostly rock) would have to becalibrated separately to determine the effect of the differentmatrix composition.1.2 The ana
4、lysis is performed after an initial drying andgrinding of the sample, and the results are reported on a drybasis. The sample preparation technique used incorporates intothe sample any rocks and organic material present in the soil.This test method of sample preparation differs from othertechniques t
5、hat involve tumbling and sieving the sample.1.3 Linear calibration is performed over a concentrationrange from 20 to 1000 g per gram for uranium and thorium.1.4 The values stated in SI units are to be regarded as thestandard. The inch-pound units in parentheses are for informa-tion only.1.5 This sta
6、ndard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.6 This in
7、ternational standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT
8、) Committee.2. Referenced Documents2.1 ASTM Standards:2C859 Terminology Relating to Nuclear MaterialsC998 Practice for Sampling Surface Soil for RadionuclidesD420 Guide for Site Characterization for Engineering De-sign and Construction PurposesD1452/D1452M Practice for Soil Exploration and Samplingb
9、y Auger BoringsD1586 Test Method for Standard Penetration Test (SPT) andSplit-Barrel Sampling of SoilsD1587/D1587M Practice for Thin-Walled Tube Sampling ofFine-Grained Soils for Geotechnical PurposesD2113 Practice for Rock Core Drilling and Sampling ofRock for Site ExplorationD3550/D3550M Practice
10、for Thick Wall, Ring-Lined, SplitBarrel, Drive Sampling of SoilsD4697 Guide for Maintaining Test Methods in the UsersLaboratory (Withdrawn 2009)3E135 Terminology Relating to Analytical Chemistry forMetals, Ores, and Related MaterialsE305 Practice for Establishing and Controlling AtomicEmission Spect
11、rochemical Analytical CurvesE456 Terminology Relating to Quality and StatisticsE876 Practice for Use of Statistics in the Evaluation ofSpectrometric Data (Withdrawn 2003)3E882 Guide for Accountability and Quality Control in theChemical Analysis Laboratory2.2 Other Document:ANSI/HPS N43.2-2001 Radiat
12、ion Safety for X-ray Diffrac-tion and X-ray Fluorescence Equipment41This test method is under the jurisdiction ofASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods ofTest.Current edition approved June 1, 2018. Published July 2018. Originally ap
13、provedin 1993. Last previous edition approved in 2011 as C1255 11. DOI: 10.1520/C1255-18.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summ
14、ary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.4Available 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 C
15、700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the
16、World Trade Organization Technical Barriers to Trade (TBT) Committee.13. Terminology3.1 Definitions:3.1.1 For definitions of terms relating to the nuclear fuelcycle, refer to Terminology C859.3.1.2 For definitions of terms relating to analytical atomicspectroscopy, refer to Terminology E135.3.1.3 Fo
17、r definitions of terms relating to statistics refer toTerminology E456.3.2 Definitions of Terms Specific to This Standard:3.2.1 escape peaka peak generated by an X-ray havingenergy greater than 1.84 keV (the energy of the k-alphaabsorption edge for silicon) that enters the detector and causesthe sil
18、icon detector crystal to fluoresce.3.2.1.1 DiscussionIf the silicon X-ray escapes thedetector, carrying with it the energy of the silicon k-alphaX-ray, 2.79 E-16 Joules J (1.74 keV), the energy measuredfor the detected X-ray will be less than the actual X-ray energyby exactly 2.79 E-16 J (1.74 keV).
19、 Therefore, as countsaccumulate for any major X-ray peak, an escape peak can beexpected to appear at an energy of 2.79 E-16 J (1.74 keV)below the major peak. Escape peaks can be calculated andremoved from the spectrum by most instrumentation software.3.2.2 flux monitor (FM) valuethe detected X-ray i
20、ntensitywithin a specified spectral range from a metallic standardgiving a high number of counts.3.2.2.1 DiscussionThe same excitation conditions as thesample analysis are used (except for the change in the currentto achieve maximum efficiency of the data acquisition system).With all conditions rema
21、ining constant, the FM value isproportional to the X-ray energy flux being emitted from theX-ray tube or radioisotope source.3.2.3 flux monitor ratio (FMR)the ratio of the initial FMvalue (FMi) prior to calibration and sample analysis to currentFM value (FMc) at the time of sample analysis.3.2.3.1 D
22、iscussionThis ratio is used to correct the mea-sured element intensity for changes in the X-ray energy flux.4. Summary of Test Method4.1 A representative sample of soil is obtained by firsttaking a sizeable amount (100 g) and drying it, then runningit through a crusher and placing it on a shaker/tum
23、bler tohomogenize it. A portion is then ground in a ball mill andpressed into a sample pellet. An energy dispersive X-rayfluorescence spectrometer is used to expose the sample to amonochromatic X-ray source capable of exciting the uraniumand thorium L-alpha series lines. The X-rays emitted by thesam
24、ple are detected via a solid state detector Si(Li) andcounted in discrete energy channels on a multi-channel ana-lyzer (MCA) to form an energy spectrum. The spectrum is thenprocessed to obtain the peak intensities for uranium andthorium for calibration and quantitation.5. Significance and Use5.1 Thi
25、s test method was developed and the instrumentcalibrated using ground soils from the site of a nuclearmaterials plant. This test method can be used to measure theextent of contamination from uranium and thorium in groundsoils. Since the detection limit of this technique (nominally 20g per gram) appr
26、oaches typical background levels for thesecontaminants, the method can be used as a quick characteriza-tion of an on-site area to indicate points of contamination.Thenafter cleanup, EDXRF may be used to verify the elimination ofcontamination or other analysis methods (such as colorimetry,fluoremetry
27、, phosphorescence, etc.) can be used if it is neces-sary to test for cleanup down to a required background level.This test method can also be used for the segregation of soillots by established contamination levels during on-site con-struction and excavation.6. Interferences6.1 The following element
28、s typically are found in an X-rayspectrum from soil in the spectral region of uranium andthorium: zinc (Zn), tungsten (W), lead (Pb), rubidium (Rb),strontium (Sr), and yttrium (Y).6.2 Rubidium is the primary interference for uranium,overlapping the uranium L-alpha-1 peak, and lead is theprimary inte
29、rference for thorium, overlapping the thoriumL-alpha-1 peak. At typical levels for these elements all of thepeak interferences can be eliminated by using a Gaussianmathematical peak fitting and deconvolution software routine.(Such is usually part of EDXRF instrumental software.)However, if the lead
30、level is high (greater than 500 g pergram), due, for instance, to the contamination of the soil bylead paint, then the peak segregation can become impossible.(A complete discussion of interelement effects and the correc-tion models used to compensate for these effects is outside thescope of this pro
31、cedure.) Explanations are found in severalsources (1, 2).56.3 Escape peaks (see 3.2.1) can interfere with the integra-tion of the uranium and thorium L-alpha peaks and aretherefore removed from the spectrum with a software operation(as is available with most instruments).7. Apparatus7.1 Energy Dispe
32、rsive X-Ray Fluorescence (EDXRF)System, refer to manufacturers literature for the selection ofthe X-ray spectrometer.7.1.1 Photon Excitation Source, capable of producingmonochromatic X-rays of an appropriate energy to efficientlyexcite uranium and thorium, that is, from 2.72 E-15 to 3.52E-15 Joules
33、J (from 17 to 22 keV). Either of the followingsources is acceptable:7.1.1.1 Radioactive Source,109Cd is well suited for efficientexcitation. It should have an activity between 2.59 E + 08 and3.70 E + 08 becquerels (between 7 and 10 millicurie).7.1.1.2 X-Ray Generator, with high voltage power supply,
34、rhodium target X-ray tube and a secondary target; molybde-num (Mo), rhodium (Rh) or silver (Ag) are suitable secondarytargets.7.1.2 Solid State Detector Si(Li), with preamplifier main-tained at appropriate temperature and capable of 2.64 E-17 J5The boldface numbers in parentheses refer to a list of
35、references at the end ofthe text.C1255 182(165 eV) FWHM resolution or better using an558Fe radioiso-tope source with 1000 cps intensity of the emitted Mn K-alphapeak 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 amplifie
36、r or pulseprocessor using a 7.5 s pulse shaping time constant; a pulsepileup rejector; an analog-to-digital converter (ADC); andmulti-channel scaler.NOTE 1Automatic correction for count rate losses due to pulse pileupor electronics deadtime is achieved in the pulse processing electronics (asis avail
37、able in most commercial X-ray units). Along with the automaticcount rate correction, the maximum efficiency of the data acquisitionsystem (that is, the preamplifier, pulse processor, andADC) is achieved ata 50 % deadtime count rate. This is based on an electronic analysis ofcounting losses by the ma
38、nufacturer. The X-ray tube current is thereforeadjusted for a given sample matrix and set of excitation conditions toachieve a 50 % deadtime.7.2 Drying Oven, controlled at 110 6 5 Celsius.7.3 Analytical Jaw Tooth Crusher, or equivalent, capable ofcrushing to 0.1 mm particle size.7.4 Laboratory Vacuu
39、m Cleaner, with a high efficiencyparticulate air (HEPA) filter element.7.5 Shaker/Tumbler, capable of blending a large volume ofdry 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 th
40、evial in 8.2.3.An equivalent process may be used to achieve theparticle size specified in the sample preparation Section 11.7.7 Hydraulic Press, 2.22 E + 05 N (25 ton-force) loadcapacity.7.8 Desiccator.8. Reagents and Materials8.1 ReagentsNone.8.2 Materials:8.2.1 Evaporating Dishes, glazed porcelain
41、, size No. 7 orlarger, with a 2.00 E-4 m3(200 mL) capacity.8.2.2 Watch Glasses, size appropriate to cover the evaporat-ing dish.8.2.3 Grinding/Mixing Vial Set, with two mixing balls,made of steel or tungsten carbide, ball diameters of nominally13 mm (0.5 in.), with a grinding sample capacity of 10 c
42、m3.Anequivalent process and set of materials may be used to achievethe same particle size specified in the sample preparationsection.8.2.4 Die Press Set, 31 mm diameter with a maximum loadcapacity in excess of 2.22 E + 05 N (25 ton-force), or asrequired for the instrument in use.8.2.5 Retaining Cup,
43、 aluminum, 32 mm diameter, suitablefor the die press, or as required for the instrument in use.9. Hazards9.1 XRF equipment analyzes by the interaction of ionizingradiation with the sample. Applicable safety regulations andstandard operating procedures must be reviewed prior to theuse of such equipme
44、nt. All modern XRF spectrometers areequipped with safety interlocks to prevent accidental penetra-tion of the X-ray beam by the user. Do NOT override theseinterlocks without proper training or a second knowledgeableperson present during sup operation. (See ANSI/HPS N43.2-2001.)9.2 When cleaning out
45、the grinder and sample mixing vialswith course sand or crushed glass, the resultant finely pow-dered glass is a health hazard if inhaled; crystalline silica cancause silicosis if exposure occurs on a regular basis. All suchoperations must be performed in a properly functioning ex-haust hood.10. Samp
46、ling, Test Specimens, and Test Units10.1 Practice C998 gives a practice for sampling of surfacesoil to obtain a representative sample for analysis of radionu-clides. Guide D420 provides a guide for investigating andsampling soil and rock materials at subsurface levels but ismainly concerned with geo
47、logical characterization. Themethod described in Test Method D1587/D1587M may beused to sample the soil using a thin-walled tube. If the soil istoo hard for pushing, the tube may be driven or PracticeD3550/D3550M may be used. The method described in TestMethod D1586 may also be used to sample the so
48、il andincludes discussion on drilling procedures and collectingsamples which are representative of the area. In the case ofsampling rocky terrain, diamond core drilling may be used (seePractice D2113). Where disturbed sampling techniques can beafforded, Practice D1452/D1452M can be used, that is, us
49、ingan Auger boring technique. The size of the sample is based onachieving a representative sample. Tube samples can becomposited to achieve such a sample. Refer to the standardsmentioned above that discuss obtaining a representativesample.11. Sample Preparation11.1 As stated in the scope, the analysis is performed on adry weight basis, however, the percent moisture of the soilsample can be determined during the following steps bymeasuring the weight before and after drying. This providesthe opportunity to calculate and report the data on an as-received basis
