1、Designation: E1172 87 (Reapproved 2011)E1172 16Standard Practice forDescribing and Specifying a Wavelength-DispersiveWavelength Dispersive X-Ray Spectrometer1This standard is issued under the fixed designation E1172; 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 () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers the components of a wavelength-dispersive wavelengt
3、h dispersive X-ray spectrometer that are basic toits operation and to the quality of its performance. It is not the intent of this practice to specify component tolerances orperformance criteria, as these are unique for each instrument. The document does, however,However, the practice does attempt t
4、oidentify which of these tolerances are critical and thus which should be specified.1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and
5、 to determine the applicability of regulatorylimitations prior to use. Specific safety hazard statements are given in 5.3.1.2 and 5.3.2.4, and in Section 7.1.3 There are several books and publications from the National Institute of Standards andTechnology2 and the U.S. GovernmentPrinting Office3,4 w
6、hich deal with the subject of X-ray safety. Refer also to Practice E416.52. Referenced Documents2.1 ASTM Standards:2E135 Terminology Relating to Analytical Chemistry for Metals, Ores, and Related MaterialsE416E2857 Practice for Planning and Safe Operation of a Spectrochemical LaboratoryGuide for Val
7、idatingAnalytical Methods(Withdrawn 2005)E876 Practice for Use of Statistics in the Evaluation of Spectrometric Data (Withdrawn 2003)63. Terminology3.1 For terminology relating to X-ray spectrometry, refer to Terminology E135.4. Significance and Use4.1 This practice describes the essential component
8、s of a wavelength-dispersive wavelength dispersive X-ray spectrometer.Thisdescription is presented so that the user or potential user may gain a cursory understanding of the structure of an X-rayspectrometer system. It also provides a means for comparing and evaluating different systems as well as u
9、nderstanding thecapabilities and limitations of each instrument.4.2 It is understood that a laboratory may implement this practice or an X-ray fluorescence method in partnership with amanufacturer of the analytical instrumentation. If a laboratory chooses to consult with an instrument manufacturer,
10、then thefollowing should be considered. The laboratory should have an idea of the alloy matrices to be analyzed, elements and massfraction ranges to be determined, and the expected performance requirements for each of these elements. The laboratory shouldinform the instrument manufacturer of these r
11、equirements so they may develop an analytical method which meets the laboratorys1 This practice is under the jurisdiction of ASTM Committee E01 on Analytical Chemistry for Metals, Ores, and Related Materials and is the direct responsibility ofSubcommittee E01.20 on Fundamental Practices.Current edit
12、ion approved Nov. 15, 2011June 1, 2016. Published June 2012June 2016. Originally approved in 1987. Last previous edition approved in 20032011 asE1172 87(2003).(2011). DOI: 10.1520/E1172-87R11.10.1520/E1172-16.2 NBS Handbook, X-Ray Protection, HB76, and NBS Handbook 111,ANSI N43.2-1971, available fro
13、m National Institute of Standards and Technology, Gaithersburg, MD20899.3 Radiation Safety Recommendations for X-Ray Diffraction and Spectrographic Equipment, No. MORP68-14, 1968, available from U.S. Department of Health, Education,and Welfare, Rockville, MD 20850.4 U.S. Government Handbook 93, Safe
14、ty Standards for Non-Medical X-Ray and Sealed Gamma-Ray Sources, Part 1, General, Superintendent of Documents, available fromU.S. Government Printing Office, Washington, DC 22025.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org.
15、For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.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. Becauseit may
16、 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 versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbo
17、r Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1expectations. Typically, instrument manufacturers customize the instrument configuration to satisfy the end-users requirements forelemental coverage, elemental precision, and detection limits. Instrument manufacturer developed ana
18、lytical methods may includespecific parameters for sample excitation, wavelengths, inter-element interference corrections, calibration and regression,equipment configuration/installation, and sample preparation requirements. Laboratories should have a basic understanding of theparameters derived by
19、the manufacturer.5. Description of Equipment5.1 Types of SpectrometersX-ray spectrometers can be classified as sequential, simultaneous, or a combinationhybrid (see5.1.3of these two (hybrid).).5.1.1 Sequential SpectrometersThe sequential spectrometer disperses and detects secondary X rays X-rays by
20、means of anadjustable monochromator called a goniometer. In flat-crystal instruments, secondary X rays are Secondary X-rays emitted fromthe specimen and nonparallel X rays pass through a mask that defines the viewed region of the specimen. Next, they enter acollimator, typically a Soller slit, and n
21、onparallel X-rays are eliminated by means of a Soller slit (collimator). being absorbed bythe blades of the collimator. The parallel beam of X rays strikes a flat X-rays strikes an analyzing crystal whichthat disperses theX rays X-rays according to their wavelengths. The dispersed X rays X-rays are
22、then measured by suitable detectors.Adjusting thegoniometer variesdetectors, which may have an attached collimator in front of the entrance window.Adjustment of the goniometerchanges the angle between the specimen, crystal, and detector, permitting the measurement of different wavelengths, and there
23、foredifferent elements. Sequential instruments containing curved-crystal optics are less common. This design substitutes curved for flatcrystals and entrance and exit slits for collimators.therefore, of different elements.5.1.2 Simultaneous SpectrometersSimultaneous spectrometers use separate monoch
24、romators to measure each element. Theseinstruments are for the most part of fixed configuration, although some simultaneous instruments have a scanning channel withlimited function. an individual monochromator to measure a selected wavelength of X- rays for each element. A typicalmonochromator consi
25、sts of an entrance slit, a curved (focusing) analyzing crystal, an exit slit, and a suitable detector. SecondaryX rays X-rays pass through the entrance slit and strike the analyzing crystal, which diffracts the wavelength of interest and focusesit through the exit slit where it is measured by to ent
26、er the detector. Some simultaneous instruments use flat crystals, but this isless common.crystals.5.1.3 Hybrid SpectrometersHybrid spectrometers combine features found in sequential and simultaneous instruments. Theyhave both fixed channels and one or more fully functional goniometers.One type uses
27、a set of fixed monochromators for key X-raylines and a goniometer for choosing other lines. Another type uses a set of fixed monochromators along with an energy dispersivedevice for choosing other lines.5.2 Spectrometer Environment:5.2.1 Temperature StabilizationA means for stabilizing the temperatu
28、re of the spectrometer shallshould be provided. Thedegree of temperature control shallshould be specified by the manufacturer. Temperature stability directly affects instrumentstability.5.2.2 Optical Path:5.2.2.1 A vacuum path is generally preferred, especially for the analysis of light elements (lo
29、ng wavelengths). measurement ofX-rays of sufficiently low energy (long wavelengths) to be absorbed by air or nitrogen. Instruments capable of vacuum operationshallshould have a vacuum gagegauge to indicate vacuum level. An airlock mechanism shall also should be provided to pumpdown evacuate the spec
30、imen chamber before opening it to the spectrometer. Pump down time shall be specified by themanufacturer.A means of controlling evacuation time is a desirable feature.5.2.2.2 A helium path is recommended when light element analysis measurement of low energy X-rays is required and thespecimen (such a
31、s a liquid) would be disturbed by a vacuum. Instruments equipped for helium operation shallshould have anairlock for flushing the specimen chamber with helium before introducing the specimen into the spectrometer. Helium flushing timeshall be specified by the manufacturer. The manufacturer shallA me
32、ans of controlling helium flush time is a desirable feature. Themanufacturer should also provide a means for accurately controlling the pressure of the helium within the spectrometer.5.2.2.3 An air path is an option when the instrument is not equipped for vacuum or helium operation. Light element an
33、alysisand some lower detection Operation with air in the optical path may be an option with some spectrometer designs.NOTE 1Some spectrometers do not allow operation in air because high X-ray flux generates ozone that damages elastomers in vacuum seals. Somespectrometers use bellows coupled to micro
34、switches as the safety interlock to prevent accidental exposure to X-rays by those repairing a spectrometerand to prevent damage resulting from operation with an air-filled optical path.limits are sacrificed when operating with an air optical path.5.3 ExcitationA specimen is excited by X rays X-ray
35、s generated by an X-ray tube which is powered by a high voltagegenerator and is usually cooled by circulating water. The intensity of the various wavelengths of X rays generator. The wavelengthdistribution and flux of X-rays striking the specimen is varied by changing the power settings to the tube
36、or by inserting filters intothe beam path.path between the tube window and the specimen position.5.3.1 X-Ray TubeThe X-ray tube may be one of two types;types: end-window or side-window. Depending upon theinstrument, either the anode or the cathode is grounded. Cathode grounding permits the window of
37、 the X-ray tube to be thinnerand thus affords more efficient transmittance of the longer excitation wavelengths.wavelengths.E1172 1625.3.1.1 X-ray tubes are produced with a variety of targets. The choice of the target material depends upon the wavelengths thatrequire excitation. X rays X-rays from c
38、ertain materials excite the longer wavelengths more efficiently. Other materials are betterfor exciting the shorter wavelengths. Generally the choice of target material is a compromise.5.3.1.2 X-ray tubes are rated according to maximum power, maximum current, and typical power settings. These should
39、 bespecified by the manufacturer. (WarningIt is important that the user be protected from exposure to harmful X rays. Standardwarning labels shall warn the user of the possibility of exposure to X rays. Safety interlock circuits (7.3) shall shut down powerto the X-ray tube whenever protective shield
40、ing is removed.)5.3.2 High Voltage GeneratorThe high voltage generator supplies power to the X-ray tube. Its stability is critical to theprecision of the instrument.5.3.2.1 The dc voltage output of the high voltage generator is typically adjustable within the range of 10 to 20 kV to 60 kV.Some desig
41、ns operate at lower voltage and some provide up to 100 kV. Voltage stability, drift with temperature, thermal drift, andvoltage ripple should be specified.Voltage repeatability should be specified for a programmable generator, which is frequently usedin sequential systems.generator.5.3.2.2 The curre
42、nt to the X-ray tube is typically adjustable within the range of 5 to 100 mA to 125 mA, with some suppliesrated up to 160 mA. Current stability and thermal drift should be specified. Current repeatability should be specified forprogrammable generators.5.3.2.3 Voltage and current recovery times shoul
43、d be specified for programmable generators. The software routines whichcontrol the generator must delay measurement until the generator recovers from voltage or current changes.5.3.2.4 Input power requirements should be specified by the manufacturer so the proper power can be supplied when theinstru
44、ment is installed. Maximum generator power output should be stated. (WarningSafety is a primary concern when dealingwith high voltage. Safety interlock circuits (7.3) and warning labels shall protect the user from coming in contact with high voltage.The interlock system shall shut down the generator
45、 when access to high voltage is attempted. Circuits shall be provided to protectthe X-ray tube from power and current overloads.)5.3.3 Water Cooling RequirementsThe X-ray tube and some high voltage generators require cooling by either filtered tapwater or a closed-loop heat exchanger system.5.3.3.1
46、The manufacturer shallshould specify water flow and quality requirements.5.3.3.2 To protect components from overheating, an interlock circuit that monitors either water coolant flow or temperature orboth shallshould shut down power to the X-ray tube whenever these requirements are not met.5.3.3.3 Wa
47、ter purity is especially critical in cathode-grounded systems since this requires because the coolant tomust benonconducting. A closed-loop heat exchanger is necessary to supply high purity cooling purity, low conductivity water. Aconductivity gage shall monitor water coolant purity in these systems
48、 and shall shut down power to gauge may be provided toprotect the X-ray tube when coolant purity is below requirements.conductivity becomes too high. The closed loop may incorporatean ion exchange resin to maintain water purity.5.3.4 Primary Beam FilterA primary beam filter is commonly used in seque
49、ntial spectrometers to filter out the characteristicemissions from the X-ray tubestube target when these emissions might interfere with the measurement of an analyte element.Primary beam filters are also useful for lowering the background in the longer wavelength (lower energy) portion of the spectrum.This serves to increase the peak to background ratio and offers greater detection of those longer wavelength X rays.to lowerdetection limits.5.3.4.1 Primary beam filters are made of several different metals (depending upon the X-ray tubestube target) and come invario
