1、Designation: C1255 11Standard 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 and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1
7、ASTM Standards:2C859 Terminology Relating to Nuclear MaterialsC998 Practice for Sampling Surface Soil for RadionuclidesD420 Guide to Site Characterization for Engineering De-sign and Construction PurposesD1452 Practice for Soil Exploration and Sampling byAugerBoringsD1586 Test Method for Penetration
8、 Test (SPT) and Split-Barrel Sampling of SoilsD1587 Practice for Thin-Walled Tube Sampling of Soils forGeotechnical PurposesD2113 Practice for Rock Core Drilling and Sampling ofRock for Site InvestigationD3550 Practice for Thick Wall, Ring-Lined, Split Barrel,Drive Sampling of SoilsD4697 Guide for M
9、aintaining Test Methods in the UsersLaboratory3E135 Terminology Relating to Analytical Chemistry forMetals, Ores, and Related MaterialsE305 Practice for Establishing and Controlling AtomicEmission Spectrochemical Analytical CurvesE456 Terminology Relating to Quality and StatisticsE876 Practice for U
10、se of Statistics in the Evaluation ofSpectrometric Data3E882 Guide for Accountability and Quality Control in theChemical Analysis Laboratory2.2 Other Document:ANSI/HPS N43.2-2001 Radiation Safety for X-ray Diffrac-tion and X-ray Fluorescence Equipment43. Terminology3.1 Definitions:3.1.1 For definiti
11、ons 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 For definitions of terms relating to statistics refer toTerminology E456.3.2 Definitions of Terms Specific to This Stand
12、ard: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 silicon detector crystal to fluoresce. If the silicon X-rayescapes the detector, carrying with it the energy of the silic
13、onk-alpha X-ray, 2.79 E-16 Joules J (1.74 keV), the energy1This test method is under the jurisdiction of ASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods ofTest.Current edition approved June 1, 2011. Published June 2011. Originallyapproved in
14、 1993. Last previous edition approved in 2005 as C1255 93 (2005).DOI: 10.1520/C1255-11.2For 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 Summar
15、y page onthe ASTM website.3Withdrawn. The last approved version of this historical standard is referencedon www.astm.org.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1Copyright ASTM International, 100 Barr Harbor Drive
16、, PO Box C700, West Conshohocken, PA 19428-2959, United States.measured for the detected X-ray will be less than the actualX-ray energy by exactly 2.79 E-16 J (1.74 keV). Therefore, ascounts accumulate for any major X-ray peak, an escape peakcan be expected to appear at an energy of 2.79 E-16 J (1.7
17、4keV) below the major peak. Escape peaks can be calculatedand removed from the spectrum by most instrumentationsoftware.3.2.2 flux monitor (FM) valuethe detected X-ray intensitywithin a specified spectral range from a metallic standardgiving a high number of counts. The same excitation condi-tions a
18、s the sample analysis are used (except for the change inthe current to achieve maximum efficiency of the data acqui-sition system). With all conditions remaining constant, the FMvalue is proportional to the X-ray energy flux being emittedfrom the X-ray tube or radioisotope source.3.2.3 flux monitor
19、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. This ratio isused to correct the measured element intensity for changes inthe X-ray energy flux.4. Summary of Test Method4.1 A representative sample of
20、soil is obtained by firsttaking a sizeable amount (100 g) and drying it, then runningit through a crusher and placing it on a shaker/tumbler 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
21、 the sample to amonochromatic X-ray source capable of exciting the uraniumand thorium L-alpha series lines. The X-rays emitted by thesample 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 spectru
22、m is thenprocessed to obtain the peak intensities for uranium andthorium for calibration and quantitation.5. Significance and Use5.1 This 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 theex
23、tent of contamination from uranium and thorium in groundsoils. Since the detection limit of this technique (nominally 20g per gram) approaches 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.
24、Thenafter cleanup, EDXRF may be used to verify the elimination ofcontamination or other analysis methods (such as colorimetry,fluoremetry, 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 segregat
25、ion of soillots by established contamination levels during on-site con-struction and excavation.6. Interferences6.1 The following elements 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),
26、 and yttrium (Y).6.2 Rubidium is the primary interference for uranium,overlapping the uranium L-alpha-1 peak, and lead is theprimary interference for thorium, overlapping the thoriumL-alpha-1 peak. At typical levels for these elements all of thepeak interferences can be eliminated by using a Gaussia
27、nmathematical peak fitting and deconvolution software routine.(Such is usually part of EDXRF instrumental software.)However, if the lead 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 co
28、mplete discussion of interelement effects and the correc-tion models used to compensate for these effects is outside thescope of this procedure.) 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
29、 and aretherefore removed from the spectrum with a software operation(as is available with most instruments).7. Apparatus7.1 Energy Dispersive X-Ray Fluorescence (EDXRF) Sys-tem, refer to manufacturers literature for the selection of theX-ray spectrometer.7.1.1 Photon Excitation Source, capable of p
30、roducingmonochromatic X-rays of an appropriate energy to efficientlyexcite uranium and thorium, that is, from 2.72 E-15 to 3.52E-15 Joules 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 ac
31、tivity 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,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),
32、with preamplifier main-tained at liquid nitrogen temperature and capable of 2.64 E-17J (165 eV) FWHM resolution or better using an558Fe radio-isotope source with 1000 cps intensity of the emitted MnK-alpha peak at 9.453 E-16 J (5.900 keV).7.1.3 Signal Processing and Data Acquisition Electronics,incl
33、udes: a bias power supply; a shaping amplifier 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
34、 the pulse processing electronics (asis available 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, and ADC) is achieved ata 50 % deadtime count rate. This is based on an e
35、lectronic analysis ofcounting losses by the manufacturer. 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.5The boldface numbers in parentheses refer to a list of references
36、 at the end ofthe text.C1255 1127.3 Analytical Jaw Tooth Crusher, or equivalent, capable ofcrushing to 0.1 mm particle size.7.4 Laboratory Vacuum 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
37、 a sample container. The shaker/tumbler may have a capacity to blend several containers.7.6 Impact Grinding/Mixing Mill, capable of accepting thevial 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 + 0
38、5 N (25 ton-force) loadcapacity.7.8 Desiccator.8. Reagents and Materials8.1 ReagentsNone.8.2 Materials:8.2.1 Evaporating Dishes, glazed porcelain, 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
39、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 cm3.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, 3
40、1 mm diameter with a maximum loadcapacity in excess of 2.22 E + 05 N (25 ton-force).8.2.5 Retaining Cup, aluminum, 32 mm diameter, suitablefor the die press.9. Hazards9.1 XRF equipment analyzes by the interaction of ionizingradiation with the sample. Applicable safety regulations andstandard operati
41、ng procedures must be reviewed prior to theuse of such equipment. 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 s
42、up operation. (See ANSI/HPS N43.2-2001.)9.2 When cleaning out 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
43、 be performed in a properly functioning ex-haust hood.10. Sampling, 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
44、materials at subsurface levels but ismainly concerned with geological characterization. Themethod described in Test Method D1587 may be used tosample the soil using a thin-walled tube. If the soil is too hardfor pushing, the tube may be driven or Practice D3550 may beused. The method described in Te
45、st Method D1586 may also beused to sample the soil and includes discussion on drillingprocedures and collecting samples which are representative ofthe area. In the case of sampling rocky terrain, diamond coredrilling may be used (see Practice D2113). Where disturbedsampling techniques can be afforde
46、d, Practice D1452 can beused, that is, using an Auger boring technique. The size of thesample is based on achieving a representative sample. Tubesamples can be composited to achieve such a sample. Refer tothe standards mentioned above that discuss obtaining a repre-sentative sample.11. Sample Prepar
47、ation11.1 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-receiv
48、ed basis or the percent moisture can be reported sepa-rately. Transfer the laboratory soil sample into an evaporatingdish and cover the dish with a watch glass. Place the evapo-rating dish into a drying oven maintained at 105 Celsius.Allow it to dry for a minimum of 18 h. Remove the dish fromthe ove
49、n and allow it to cool to room temperature.NOTE 2It is recommended that a sample preparation log be developedand implemented by the user which details and tracks the steps ofpreparation for each sample. For each sample, the sample preparation logwould list: the jaw tooth crusher; mixing vial number; grinder/mixingmill; and die press set used, as well as the preparers name, and the dateand time of preparation. Such a log is useful in backtracking crosscontamination or sample carry over problems that are detected from theblank, standard, and control sample data
