1、Designation: E1172 87 (Reapproved 2011)Standard Practice forDescribing and Specifying a Wavelength-Dispersive X-RaySpectrometer1This standard is issued under the fixed designation E1172; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisi
2、on, 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 practice covers the components of a wavelength-dispersive X-ray spectrometer that are basic to it
3、s operationand to the quality of its performance. It is not the intent of thispractice to specify component tolerances or performancecriteria, as these are unique for each instrument. The documentdoes, however, attempt to identify which of these are criticaland thus which should be specified.1.2 Thi
4、s 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. Specific safetyhazard
5、 statements are given in 5.3.1.2 and 5.3.2.4, and inSection 7.1.3 There are several books and publications from theNational Institute of Standards and Technology2and the U.S.Government Printing Office3,4which deal with the subject ofX-ray safety. Refer also to Practice E416.52. Referenced Documents2
6、.1 ASTM Standards:5E135 Terminology Relating to Analytical Chemistry forMetals, Ores, and Related MaterialsE416 Practice for Planning and Safe Operation of a Spec-trochemical Laboratory6E876 Practice for Use of Statistics in the Evaluation ofSpectrometric Data63. Terminology3.1 For terminology relat
7、ing to X-ray spectrometry, refer toTerminology E135.4. Significance and Use4.1 This practice describes the essential components of awavelength-dispersive X-ray spectrometer. This description ispresented so that the user or potential user may gain a cursoryunderstanding of the structure of an X-ray s
8、pectrometer sys-tem. It also provides a means for comparing and evaluatingdifferent systems as well as understanding the capabilities andlimitations of each instrument.5. Description of Equipment5.1 Types of SpectrometersX-ray spectrometers can beclassified as sequential, simultaneous, or a combinat
9、ion ofthese two (hybrid).5.1.1 Sequential SpectrometersThe sequential spectrom-eter disperses and detects secondary X rays by means of anadjustable monochromator called a goniometer. In flat-crystalinstruments, secondary X rays are emitted from the specimenand nonparallel X rays are eliminated by me
10、ans of a Soller slit(collimator). The parallel beam of X rays strikes a flatanalyzing crystal which disperses the X rays according to theirwavelengths. The dispersed X rays are then measured bysuitable detectors. Adjusting the goniometer varies the anglebetween the specimen, crystal, and detector, p
11、ermitting themeasurement of different wavelengths and therefore differentelements. Sequential instruments containing curved-crystaloptics are less common. This design substitutes curved for flatcrystals and entrance and exit slits for collimators.5.1.2 Simultaneous SpectrometersSimultaneous spec-tro
12、meters use separate monochromators to measure each ele-ment. These instruments are for the most part of fixed1This practice is under the jurisdiction of ASTM Committee E01 on AnalyticalChemistry for Metals, Ores, and Related Materials and is the direct responsibility ofSubcommittee E01.20 on Fundame
13、ntal Practices.Current edition approved Nov. 15, 2011. Published June 2012. Originallyapproved in 1987. Last previous edition approved in 2003 as E1172 87(2003).DOI: 10.1520/E1172-87R11.2NBS Handbook, X-Ray Protection, HB76, and NBS Handbook 111, ANSIN43.2-1971, available from National Institute of
14、Standards and Technology,Gaithersburg, MD 20899.3Radiation Safety Recommendations for X-Ray Diffraction and SpectrographicEquipment, No. MORP 68-14, 1968, available from U.S. Department of Health,Education, and Welfare, Rockville, MD 20850.4U.S. Government Handbook 93, Safety Standards for Non-Medic
15、al X-Ray andSealed Gamma-Ray Sources, Part 1, General, Superintendent of Documents,available from U.S. Government Printing Office, Washington, DC 22025.5For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMSta
16、ndards volume information, refer to the standards Document Summary page onthe ASTM website.6Withdrawn. The last approved version of this historical standard is referencedon www.astm.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States
17、.configuration, although some simultaneous instruments have ascanning channel with limited function. A typical monochro-mator consists of an entrance slit, a curved (focusing) analyz-ing crystal, an exit slit, and a suitable detector. Secondary Xrays pass through the entrance slit and strike the ana
18、lyzingcrystal, which diffracts the wavelength of interest and focusesit through the exit slit where it is measured by the detector.Some simultaneous instruments use flat crystals, but this is lesscommon.5.1.3 Hybrid SpectrometersHybrid spectrometers com-bine features found in sequential and simultan
19、eous instru-ments. They have both fixed channels and one or more fullyfunctional goniometers.5.2 Spectrometer Environment:5.2.1 Temperature StabilizationA means for stabilizingthe temperature of the spectrometer shall be provided. Thedegree of temperature control shall be specified by the manu-factu
20、rer. Temperature stability directly affects instrument sta-bility.5.2.2 Optical Path:5.2.2.1 A vacuum path is generally preferred, especially forthe analysis of light elements (long wavelengths). Instrumentscapable of vacuum operation shall have a vacuum gage toindicate vacuum level. An airlock mech
21、anism shall also beprovided to pump down the specimen chamber before openingit to the spectrometer. Pump down time shall be specified bythe manufacturer.5.2.2.2 A helium path is recommended when light elementanalysis is required and the specimen (such as a liquid) wouldbe disturbed by a vacuum. Inst
22、ruments equipped for heliumoperation shall have an airlock for flushing the specimenchamber with helium before introducing the specimen into thespectrometer. Helium flushing time shall be specified by themanufacturer. The manufacturer shall also provide a means foraccurately controlling the pressure
23、 of the helium within thespectrometer.5.2.2.3 An air path is an option when the instrument is notequipped for vacuum or helium operation. Light elementanalysis and some lower detection limits are sacrificed whenoperating with an air optical path.5.3 ExcitationA specimen is excited by X rays generate
24、dby an X-ray tube which is powered by a high voltage generatorand is usually cooled by circulating water. The intensity of thevarious wavelengths of X rays striking the specimen is variedby changing the power settings to the tube or by inserting filtersinto the beam path.5.3.1 X-Ray TubeThe X-ray tu
25、be may be one of twotypes; end-window or side-window. Depending upon the in-strument, either the anode or the cathode is grounded. Cathodegrounding permits the window of the X-ray tube to be thinnerand thus affords more efficient transmittance of the longerexcitation wavelengths.5.3.1.1 X-ray tubes
26、are produced with a variety of targets.The choice of the target material depends upon the wave-lengths that require excitation. X rays from certain materialsexcite the longer wavelengths more efficiently. Other materialsare better for exciting the shorter wavelengths. Generally thechoice of target m
27、aterial is a compromise.5.3.1.2 X-ray tubes are rated according to maximum power,maximum current, and typical power settings. These should bespecified by the manufacturer. (WarningIt is important thatthe user be protected from exposure to harmful X rays.Standard warning labels shall warn the user of
28、 the possibility ofexposure to X rays. Safety interlock circuits (7.3) shall shutdown power to the X-ray tube whenever protective shielding isremoved.)5.3.2 High Voltage GeneratorThe high voltage generatorsupplies power to the X-ray tube. Its stability is critical to theprecision of the instrument.5
29、.3.2.1 The dc voltage output of the high voltage generatoris typically adjustable within the range of 10 to 100 kV. Voltagestability, drift with temperature, and voltage ripple should bespecified. Voltage repeatability should be specified for aprogrammable generator, which is frequently used in sequ
30、en-tial systems.5.3.2.2 The current to the X-ray tube is typically adjustablewithin the range of 5 to 100 mA. Current stability and thermaldrift should be specified. Current repeatability should bespecified for programmable generators.5.3.2.3 Voltage and current recovery times should be speci-fied f
31、or programmable generators. The software routines whichcontrol the generator must delay measurement until the gen-erator recovers from voltage or current changes.5.3.2.4 Input power requirements should be specified by themanufacturer so the proper power can be supplied when theinstrument is installe
32、d. Maximum generator power outputshould be stated. (WarningSafety is a primary concernwhen dealing with high voltage. Safety interlock circuits (7.3)and warning labels shall protect the user from coming incontact with high voltage. The interlock system shall shutdown the generator when access to hig
33、h voltage is attempted.Circuits shall be provided to protect the X-ray tube from powerand current overloads.)5.3.3 Water Cooling RequirementsThe X-ray tube andsome high voltage generators require cooling by either filteredtap water or a closed-loop heat exchanger system.5.3.3.1 The manufacturer shal
34、l specify water flow andquality requirements.5.3.3.2 To protect components from overheating, an inter-lock circuit that monitors either water coolant flow or tempera-ture or both shall shut down power to the X-ray tube wheneverthese requirements are not met.5.3.3.3 Water purity is especially critica
35、l in cathode-grounded systems since this requires the coolant to be noncon-ducting. A closed-loop heat exchanger is necessary to supplyhigh purity cooling water. A conductivity gage shall monitorwater coolant purity in these systems and shall shut downpower to the X-ray tube when coolant purity is b
36、elow require-ments.5.3.4 Primary Beam FilterA primary beam filter is com-monly used in sequential spectrometers to filter out thecharacteristic emissions from the X-ray tubes target whenthese emissions might interfere with the measurement of ananalyte element. Primary beam filters are also useful fo
37、rlowering the background in the longer wavelength portion ofE1172 87 (2011)2the spectrum. This serves to increase the peak to backgroundratio and offers greater detection of those longer wavelength Xrays.5.3.4.1 Primary beam filters are made of several differentmetals (depending upon the X-ray tubes
38、 target) and come invarious thicknesses. The manufacturer should specify the type,thickness, and location of the primary beam filter.5.4 Sample PositioningThe process of positioning aspecimen in a spectrometer for analysis involves severalcomponents; the specimen holder, the specimen changer, andthe
39、 specimen rotation mechanism (spinner). These componentscontribute collectively to the reproducibility of positioning thespecimen in the optical path and thus, to instrument precision.The design of these components should therefore be regardedcritically.5.4.1 Reproducibility of the distance between
40、the face of thespecimen and the window of the X-ray tube is especiallycritical and should be specified by the manufacturer.5.4.2 The spinner rotates the specimen while it is beingexposed to the X-ray beam and thus helps to minimize theinfluence of surface defects and specimen inhomogeneity onanalyti
41、cal results.5.4.3 Imperfections in the surface of the specimen have thegreatest effect on analytical results in spectrometers with ashallow angle of irradiation or take-off angle. The manufac-turer shall specify these angles.5.4.4 Other important specifications include maximumspecimen size (thicknes
42、s and diameter) and the specimenrotation speed (if the instrument is equipped with a spinner).5.5 DispersionThe analyzing crystal is the dispersivedevice in a wavelength-dispersive X-ray spectrometer. Variouscrystals having a variety of interplanar spacings are used todisperse the specimens characte
43、ristic wavelengths.5.5.1 Sequential spectrometers may contain several differentcrystals mounted on a crystal changer mechanism. Thus, theanalyst is able to select a specific crystal for the wavelengthbeing measured.5.5.2 Each monochromator in a simultaneous instrumenthas a separate specified crystal
44、. The selection is made inaccordance with the expected analytical requirements. Thecrystal is generally bent and ground to a curve or a logarithmicspiral in order to focus the analytical line through the mono-chromators exit slit.5.5.3 The manufacturer should specify each of the crystalsinstalled in
45、 a particular spectrometer according to composition,location (which monochromator or crystal changer position),lattice orientation (when applicable), interplanar spacing, andshape (flat or curved).5.5.4 The manufacturer shall provide an adjustment forrotating the crystal to peak the spectrometer or
46、monochroma-tor.5.6 Beam Moderating Devices:5.6.1 Soller SlitsSoller slits are provided for systemscontaining flat crystals. They are composed of a series ofclosely-spaced, thin, parallel plates or tubes. When a Soller slitis placed in the path of a beam of X rays, only those X rays thatare parallel
47、to the plates or tubes will pass through the slit.Therefore, the X rays that exit the slit are parallel.5.6.1.1 Soller slits may be present in several locations. Aprimary Soller slit is always present in the optical path betweenthe specimen and the analyzing crystal. Auxiliary slits may beinstalled
48、at the detector windows between the detector and theanalyzing crystal.5.6.1.2 It is common for a sequential spectrometer to haveboth coarse and fine primary Soller slits, installed and mountedin a changer mechanism. Better resolution is achieved with afine slit, but at the expense of a loss of inten
49、sity.5.6.1.3 The manufacturer should specify the location andplate spacing of all Soller slits installed in a particularinstrument. A means shall be provided for adjusting (peaking)each slit.5.6.2 Entrance and Exit SlitsBoth entrance and exit slitsare required in a curved-crystal spectrometer. The curvedcrystal establishes a focusing circle that is similar to theRowland circle defined by a grating in an optical emissionspectrograph. In an X-ray spectrometer, however, proper fo-cusing requires that both slits not only be on the focusing circlebut also have identic
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