1、Designation: C 1255 93 (Reapproved 2005)Standard Test Method forAnalysis of Uranium and Thorium in Soils by EnergyDispersive X-Ray Fluorescence Spectroscopy1This standard is issued under the fixed designation C 1255; the number immediately following the designation indicates the year oforiginal adop
2、tion or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the energy dispersive X-rayfluorescence (EDXRF)
3、 spectrochemical analysis 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 co
4、mposition.1.2 The analysis 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 f
5、rom othertechniques that 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-t
6、ion only.1.5 This standard 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. Ref
7、erenced Documents2.1 ASTM Standards:2C 982 Guide for Selecting Components for Energy Disper-sive X-Ray Fluorescence (XRF) SystemsC 998 Practice for Sampling Surface Soil for RadionuclidesD 420 Guide for Investigating and Sampling Soil and RockD 1452 Practice for Soil Investigation and Sampling byAug
8、er BoringsD 1586 Test Method for Penetration Test and Split-BarrelSampling of SoilsD 1587 Practice for Thin-Walled Tube Sampling of SoilsD2113 Practice for Diamond Core Drilling for Site Inves-tigationD 3550 Practice for Ring-Lined Barrel Sampling of SoilsD 4697 Guide for Maintaining Test Methods in
9、 the UsersLaboratoryE 135 Terminology Relating to Analytical Chemistry forMetals, Ores, and Related MaterialsE 305 Practice for Establishing and Controlling Spectro-chemical Analytical CurvesE 456 Terminology Relating to Quality and StatisticsE 876 Practice for Use of Statistics in the Evaluation of
10、Spectrometric DataE 882 Guide for Accountability and Quality Control in theChemical Analysis Laboratory2.2 Other Document:NBS Radiation Safety Handbook Number 111 for X-RayDiffraction and Fluorescence Analysis Equipment33. Terminology3.1 Definitions:3.1.1 For definitions of terms relating to analyti
11、cal atomicspectroscopy, refer to Terminology E 135.3.1.2 For definitions of terms relating to statistics refer toTerminology E 456.3.2 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
12、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 siliconk-alpha X-ray, 2.79 E-16 Joules J (1.74 keV), the energymeasured for the detected X-ray will be less than the actualX-ra
13、y 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 (1.741This test method is under the jurisdiction of ASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Sub
14、committee C26.05 on Methods ofTests.Current edition approved June 1, 2005. Published December 2005. Originallyapproved in 1993. Last previous edition approved in 1999 as C 125593(1999).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceast
15、m.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from the U.S. Department of Commerce, National Institute ofStandards and Technology, Gaithersburg, MD 20899.1Copyright ASTM International, 100 Barr Harbor Drive, PO
16、Box C700, West Conshohocken, PA 19428-2959, United States.keV) below the major peak. Escape peaks can be calculatedand removed from the spectrum by most insrumentationsoftware.3.2.2 flux monitor (FM) valuethe detected X-ray intensitywithin a specified spectral range from a metallic standardgiving a
17、high number of counts. The same excitation condi-tions as 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 t
18、he X-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. This ratio isused to correct the measured element intensity for changes inthe X-ray energy flux.
19、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/tumbler tohomogenize it. A portion is then ground in a ball mill andpressed into a sample pellet. An energy dis
20、persive 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 thesample are detected via a solid state detector Si(Li) andcounted in discrete energy channels on a multi-channel
21、 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 This test method was developed and the instrumentcalibrated using ground soils from the site of a nuclearmateri
22、als 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) approaches typical background levels for thesecontaminants, the method can be used as a quick characteriza-tion
23、of an on-site area to indicated points of contamination.Then after cleanup, EDXRF may be used to verify theelimination of contamination or other analysis methods (suchas colorimetry, fluoremetry, phosphorescence, etc.) can be usedif it is necessary to test for cleanup down to a requiredbackground le
24、vel. This test method can also be used for thesegregation of soil lots by established contamination levelsduring on-site construction 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), t
25、ungsten (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 interference for thorium, overlapping the thoriumL-alpha-1 peak. At typical levels for these elements all of thepe
26、ak 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 level is high (greater than 500 g pergram), due, for instance, to the contamination of the soil bylead paint,
27、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 procedure.) Explanations are found in severalsources (1, 2).46.3 Escape peaks (see 3.2.1) can interfere with the
28、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 Dispersive X-Ray Fluorescence (EDXRF) Sys-tem, refer to Guide C 982.7.1.1 Photon Excitation Source, capable of prod
29、ucingmonochromatic 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). Refer to Section 8 ofGuide C 982. Either of the following sources is acceptable:7.1.1.1 Radioactive Source, 109-Cd is well suited for effi-ci
30、ent excitation. It should have an activity between 2.59 E + 08and 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; molybde-num (Mo), rhodium (Rh) or silver (Ag) are suitable secondarytargets
31、.7.1.2 Solid State Detector Si(Li), with preamplifier main-tained at liquid nitrogen temperature and capable of 2.64 E-17J (165 eV) FWHM resolution or better using an Fe-55radioisotope 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 an
32、d Data Acquisition Electronics,includes: 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
33、electronics deadtime is achieved in 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 % deadtim
34、e count rate. This is based on an electronic 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.7.3 Analytical Jaw Tooth Crushe
35、r, or equivalent, capable ofcrushing to 0.1 mm particle size.7.4 Laboratory Vacuum Cleaner, with a high efficiencyparticulate air (HEPA) filter element.4The boldface numbers in parentheses refer to a list of references at the end ofthe text.C 1255 93 (2005)27.5 Shaker/Tumbler, capable of blending a
36、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 thevial in 8.2.3. An equivalent process may be used to achieve theparticle size specified in the sample preparation
37、 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, size No. 7 orlarger, with a 2.00 E-4 m3(200 mL) capacity.8.2.2 Watch Glasses, size appropriate to cover the ev
38、aporat-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 cm3.Anequivalent process and set of materials may be used to achievethe same particle size specified in the sampl
39、e 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).8.2.5 Retaining Cup, aluminum, 32 mm diameter, suitablefor the die press.9. Hazards9.1 Refer to NBS Radiation Safety Handbook Number 111and the Hazard Section of Guide C 982
40、 for the hazardsassociated with the use of X-ray equipment.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
41、suchoperations must be performed in a properly functioning ex-haust hood.10. Sampling, Test Specimens, and Test Units10.1 Practice C 998 gives a practice for sampling of surfacesoil to obtain a representative sample for analysis of radionu-clides. Guide D 420 provides a guide for investigating andsa
42、mpling soil and rock materials at subsurface levels but ismainly concerned with geological characterization. Themethod described in Test Method D 1587 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 D 3550 may beused. The
43、 method described in Test Method D 1586 may alsobe used 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 t
44、echniques can be afforded, Practice D 1452 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
45、 sample.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
46、 the data on an as-received 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. Re
47、move the dish fromthe oven 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 cru
48、sher; 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 (see 13.2
49、). When multiple piecesof equipment are used for any one of the processing steps, the equipmentshould be numbered and the vials and die sets should be scribed withnumbers for tracking purposes.11.2 A Geiger-Muller counter may be used to survey thedried soil as a means of segregating any with a high level ofcontamination. High activity level samples can then be pre-pared on a separate jaw tooth crusher, if available, and thecleaning process can be done twice to ensure against crosscontamination.NOTE 3The count rate used to denote a high level sample will dependon
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