ASTM E1172-87(2011)
(Practice)Standard Practice for Describing and Specifying a Wavelength-Dispersive X-Ray Spectrometer
Standard Practice for Describing and Specifying a Wavelength-Dispersive X-Ray Spectrometer
SIGNIFICANCE AND USE
This practice describes the essential components of a wavelength-dispersive X-ray spectrometer. This description is presented so that the user or potential user may gain a cursory understanding of the structure of an X-ray spectrometer system. It also provides a means for comparing and evaluating different systems as well as understanding the capabilities and limitations of each instrument.
SCOPE
1.1 This practice covers the components of a wavelength-dispersive X-ray spectrometer that are basic to its operation and to the quality of its performance. It is not the intent of this practice to specify component tolerances or performance criteria, as these are unique for each instrument. The document does, however, attempt to identify which of these 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 responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations 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 and Technology and the U.S. Government Printing Office , which deal with the subject of X-ray safety. Refer also to Practice E416.
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Standards Content (Sample)
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Designation: E1172 − 87(Reapproved 2011)
Standard Practice for
Describing and Specifying a Wavelength-Dispersive X-Ray
Spectrometer
This standard is issued under the fixed designation E1172; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope trochemical Laboratory (Withdrawn 2005)
E876 Practice for Use of Statistics in the Evaluation of
1.1 This practice covers the components of a wavelength-
Spectrometric Data (Withdrawn 2003)
dispersive X-ray spectrometer that are basic to its operation
and to the quality of its performance. It is not the intent of this
3. Terminology
practice to specify component tolerances or performance
3.1 For terminology relating to X-ray spectrometry, refer to
criteria, as these are unique for each instrument. The document
Terminology E135.
does, however, attempt to identify which of these are critical
and thus which should be specified.
4. Significance and Use
1.2 This standard does not purport to address all of the
4.1 This practice describes the essential components of a
safety concerns, if any, associated with its use. It is the
wavelength-dispersive X-ray spectrometer. This description is
responsibility of the user of this standard to establish appro-
presented so that the user or potential user may gain a cursory
priate safety and health practices and determine the applica-
understanding of the structure of an X-ray spectrometer sys-
bility of regulatory limitations prior to use. Specific safety
tem. It also provides a means for comparing and evaluating
hazard statements are given in 5.3.1.2 and 5.3.2.4, and in
different systems as well as understanding the capabilities and
Section 7.
limitations of each instrument.
1.3 There are several books and publications from the
National Institute of Standards and Technology and the U.S.
5. Description of Equipment
3,4
Government Printing Office which deal with the subject of
5.1 Types of Spectrometers—X-ray spectrometers can be
X-ray safety. Refer also to Practice E416.
classified as sequential, simultaneous, or a combination of
2. Referenced Documents these two (hybrid).
5.1.1 Sequential Spectrometers—The sequential spectrom-
2.1 ASTM Standards:
eter disperses and detects secondary X rays by means of an
E135 Terminology Relating to Analytical Chemistry for
adjustable monochromator called a goniometer. In flat-crystal
Metals, Ores, and Related Materials
instruments, secondary X rays are emitted from the specimen
E416 Practice for Planning and Safe Operation of a Spec-
and nonparallel X rays are eliminated by means of a Soller slit
(collimator). The parallel beam of X rays strikes a flat
analyzing crystal which disperses the X rays according to their
This practice is under the jurisdiction of ASTM Committee E01 on Analytical
wavelengths. The dispersed X rays are then measured by
Chemistry for Metals, Ores, and Related Materials and is the direct responsibility of
Subcommittee E01.20 on Fundamental Practices. suitable detectors. Adjusting the goniometer varies the angle
Current edition approved Nov. 15, 2011. Published June 2012. Originally
between the specimen, crystal, and detector, permitting the
approved in 1987. Last previous edition approved in 2003 as E1172 – 87(2003).
measurement of different wavelengths and therefore different
DOI: 10.1520/E1172-87R11.
elements. Sequential instruments containing curved-crystal
NBS Handbook, X-Ray Protection, HB76, and NBS Handbook 111, ANSI
N43.2-1971, available from National Institute of Standards and Technology,
optics are less common. This design substitutes curved for flat
Gaithersburg, MD 20899.
crystals and entrance and exit slits for collimators.
Radiation Safety Recommendations for X-Ray Diffraction and Spectrographic
5.1.2 Simultaneous Spectrometers—Simultaneous spec-
Equipment, No. MORP 68-14, 1968, available from U.S. Department of Health,
Education, and Welfare, Rockville, MD 20850. trometers use separate monochromators to measure each ele-
U.S. Government Handbook 93, Safety Standards for Non-Medical X-Ray and
ment. These instruments are for the most part of fixed
Sealed Gamma-Ray Sources, Part 1, General, Superintendent of Documents,
configuration, although some simultaneous instruments have a
available from U.S. Government Printing Office, Washington, DC 22025.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1172 − 87 (2011)
scanning channel with limited function. A typical monochro- 5.3.1.2 X-ray tubes are rated according to maximum power,
mator consists of an entrance slit, a curved (focusing) analyz- maximum current, and typical power settings. These should be
ing crystal, an exit slit, and a suitable detector. Secondary X specified by the manufacturer. (Warning—It is important that
rays pass through the entrance slit and strike the analyzing the user be protected from exposure to harmful X rays.
crystal, which diffracts the wavelength of interest and focuses
Standardwarninglabelsshallwarntheuserofthepossibilityof
it through the exit slit where it is measured by the detector. exposure to X rays. Safety interlock circuits (7.3) shall shut
Some simultaneous instruments use flat crystals, but this is less
down power to the X-ray tube whenever protective shielding is
common. removed.)
5.1.3 Hybrid Spectrometers—Hybrid spectrometers com-
5.3.2 High Voltage Generator—The high voltage generator
bine features found in sequential and simultaneous instru-
supplies power to the X-ray tube. Its stability is critical to the
ments. They have both fixed channels and one or more fully
precision of the instrument.
functional goniometers.
5.3.2.1 The dc voltage output of the high voltage generator
istypicallyadjustablewithintherangeof10to100kV.Voltage
5.2 Spectrometer Environment:
stability, drift with temperature, and voltage ripple should be
5.2.1 Temperature Stabilization—A means for stabilizing
specified. Voltage repeatability should be specified for a
the temperature of the spectrometer shall be provided. The
programmable generator, which is frequently used in sequen-
degree of temperature control shall be specified by the manu-
tial systems.
facturer. Temperature stability directly affects instrument sta-
bility. 5.3.2.2 The current to the X-ray tube is typically adjustable
within the range of 5 to 100 mA. Current stability and thermal
5.2.2 Optical Path:
drift should be specified. Current repeatability should be
5.2.2.1 Avacuum path is generally preferred, especially for
specified for programmable generators.
the analysis of light elements (long wavelengths). Instruments
5.3.2.3 Voltage and current recovery times should be speci-
capable of vacuum operation shall have a vacuum gage to
fiedforprogrammablegenerators.Thesoftwareroutineswhich
indicate vacuum level. An airlock mechanism shall also be
control the generator must delay measurement until the gen-
provided to pump down the specimen chamber before opening
erator recovers from voltage or current changes.
it to the spectrometer. Pump down time shall be specified by
the manufacturer. 5.3.2.4 Input power requirements should be specified by the
5.2.2.2 A helium path is recommended when light element manufacturer so the proper power can be supplied when the
instrument is installed. Maximum generator power output
analysis is required and the specimen (such as a liquid) would
be disturbed by a vacuum. Instruments equipped for helium should be stated. (Warning—Safety is a primary concern
when dealing with high voltage. Safety interlock circuits (7.3)
operation shall have an airlock for flushing the specimen
chamber with helium before introducing the specimen into the and warning labels shall protect the user from coming in
contact with high voltage. The interlock system shall shut
spectrometer. Helium flushing time shall be specified by the
manufacturer. The manufacturer shall also provide a means for down the generator when access to high voltage is attempted.
Circuits shall be provided to protect the X-ray tube from power
accurately controlling the pressure of the helium within the
spectrometer. and current overloads.)
5.2.2.3 An air path is an option when the instrument is not 5.3.3 Water Cooling Requirements—The X-ray tube and
equipped for vacuum or helium operation. Light element
some high voltage generators require cooling by either filtered
analysis and some lower detection limits are sacrificed when tap water or a closed-loop heat exchanger system.
operating with an air optical path.
5.3.3.1 The manufacturer shall specify water flow and
quality requirements.
5.3 Excitation—A specimen is excited by X rays generated
5.3.3.2 To protect components from overheating, an inter-
by an X-ray tube which is powered by a high voltage generator
lock circuit that monitors either water coolant flow or tempera-
and is usually cooled by circulating water. The intensity of the
ture or both shall shut down power to the X-ray tube whenever
various wavelengths of X rays striking the specimen is varied
these requirements are not met.
bychangingthepowersettingstothetubeorbyinsertingfilters
into the beam path. 5.3.3.3 Water purity is especially critical in cathode-
5.3.1 X-Ray Tube—TheX-raytubemaybeoneoftwotypes; grounded systems since this requires the coolant to be noncon-
ducting. A closed-loop heat exchanger is necessary to supply
end-window or side-window. Depending upon the instrument,
eithertheanodeorthecathodeisgrounded.Cathodegrounding high purity cooling water. A conductivity gage shall monitor
water coolant purity in these systems and shall shut down
permits the window of the X-ray tube to be thinner and thus
affords more efficient transmittance of the longer excitation power to the X-ray tube when coolant purity is below require-
ments.
wavelengths.
5.3.1.1 X-ray tubes are produced with a variety of targets. 5.3.4 Primary Beam Filter—A primary beam filter is com-
The choice of the target material depends upon the wave- monly used in sequential spectrometers to filter out the
lengths that require excitation. X rays from certain materials characteristic emissions from the X-ray tube’s target when
excite the longer wavelengths more efficiently. Other materials these emissions might interfere with the measurement of an
are better for exciting the shorter wavelengths. Generally the analyte element. Primary beam filters are also useful for
choice of target material is a compromise. lowering the background in the longer wavelength portion of
E1172 − 87 (2011)
the spectrum. This serves to increase the peak to background are parallel to the plates or tubes will pass through the slit.
ratio and offers greater detection of those longer wavelength X Therefore, the X rays that exit the slit are parallel.
rays.
5.6.1.1 Soller slits may be present in several locations. A
primarySollerslitisalwayspresentintheopticalpathbetween
5.3.4.1 Primary beam filters are made of several different
the specimen and the analyzing crystal. Auxiliary slits may be
metals (depending upon the X-ray tube’s target) and come in
installed at the detector windows between the detector and the
various thicknesses. The manufacturer should specify the type,
analyzing crystal.
thickness, and location of the primary beam filter.
5.6.1.2 It is common for a sequential spectrometer to have
5.4 Sample Positioning—Theprocessofpositioningaspeci-
both coarse and fine primary Soller slits, installed and mounted
men in a spectrometer for analysis involves several compo-
in a changer mechanism. Better resolution is achieved with a
nents; the specimen holder, the specimen changer, and the
fine slit, but at the expense of a loss of intensity.
specimen rotation mechanism (spinner). These components
5.6.1.3 The manufacturer should specify the location and
contribute collectively to the reproducibility of positioning the
plate spacing of all Soller slits installed in a particular
specimen in the optical path and thus, to instrument precision.
instrument. A means shall be provided for adjusting (peaking)
The design of these components should therefore be regarded
each slit.
critically.
5.6.2 Entrance and Exit Slits—Both entrance and exit slits
5.4.1 Reproducibilityofthedistancebetweenthefaceofthe
are required in a curved-crystal spectrometer. The curved
specimen and the window of the X-ray tube is especially
crystal establishes a focusing circle that is similar to the
critical and should be specified by the manufacturer.
Rowland circle defined by a grating in an optical emission
5.4.2 The spinner rotates the specimen while it is being
spectrograph. In an X-ray spectrometer, however, proper fo-
exposed to the X-ray beam and thus helps to minimize the
cusing requires that both slits not only be on the focusing circle
influence of surface defects and specimen inhomogeneity on
but also have identical chordal distances from the slits to the
analytical results.
crystal. A detector is aimed at the crystal through the exit slit.
5.4.3 Imperfections in the surface of the specimen have the
5.6.2.1 The manufacturer should specify the size of the
greatest effect on analytical results in spectrometers with a
entrance and exit slit for each monochromator and shall
shallow angle of irradiation or take-off angle. The manufac-
provide adjustments to peak each monochromator. Depending
turer shall specify these angles.
upon the manufacturer, peaking may involve movement of the
5.4.4 Other important specifications include maximum
crystal, the exit slit, or both.
specimen size (thickness and diameter) and the specimen
5.6.3 Apertures—Inflat-crystalspectrometers,anapertureis
rotation speed (if the instrument is equipped with a spinner).
placed at the point in the optical path where the secondary X
rays exit the specimen. The aperture limits the area of the
5.5 Dispersion—The analyzing crystal is the dispersive
specimen seen by the detector. In some instruments, the size of
device in a wavelength-dispersive X-ray spectrometer. Various
this aperture is fixed, but in most it can be varied, either by
crystals having a variety of interplanar spacings are used to
manual replacement or a mechanical changer. The manufac-
disperse the
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