ASTM E1172-22

Standard Practice for Describing and Specifying a Wavelength Dispersive X-Ray Spectrometer

SIGNIFICANCE AND USE
4.1 This practice describes the essential components of a wavelength dispersive X-ray spectrometer. This description is presented so that the user may gain a general 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.  
4.2 A laboratory may implement this practice or an X-ray fluorescence method in partnership with a manufacturer of the analytical instrumentation. If a laboratory chooses to consult with an instrument manufacturer, then the following should be considered. The laboratory should know the alloy matrices to be analyzed, elements and mass fraction ranges to be determined, and the expected performance requirements for each of these elements. The laboratory should inform the instrument manufacturer of these requirements so an analytical method may be developed which meets the laboratory’s expectations. Typically, instrument manufacturers customize the instrument configuration to satisfy the end-user’s requirements for elemental coverage, elemental precision, and detection limits. Instrument manufacturer developed analytical methods may include specific 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 the parameters derived by the manufacturer.
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. However, the practice does attempt to identify which 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 responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Specific safety hazard statements are given in Section 7.  
1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Nov-2022
• ICS: 17.180.30 - Optical measuring instruments
• Technical Committee: E01 - Analytical Chemistry for Metals, Ores, and Related Materials
• Drafting Committee: E01.20 - Fundamental Practices

Relations

• Refers: ASTM E135-20 - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 01-Jan-2020
• Refers: ASTM E135-19 - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 15-May-2019
• Refers: ASTM E135-16 - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 15-May-2016
• Refers: ASTM E135-15a - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 01-Jul-2015
• Refers: ASTM E135-15 - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 15-May-2015
• Refers: ASTM E135-14b - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 15-Aug-2014
• Refers: ASTM E135-14a - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 01-Apr-2014
• Refers: ASTM E135-14 - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 15-Feb-2014
• Refers: ASTM E135-13a - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 01-Dec-2013
• Refers: ASTM E2857-11 - Standard Guide for Validating Analytical Methods
• Effective Date: 01-Nov-2011
• Refers: ASTM E135-11b - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 15-Sep-2011
• Refers: ASTM E135-11a - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 15-Jun-2011
• Refers: ASTM E135-11 - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 15-Jan-2011
• Refers: ASTM E135-10b - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 01-Jul-2010
• Refers: ASTM E135-10a - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 15-Jan-2010

Overview

ASTM E1172-22 is the internationally recognized standard practice for describing and specifying a wavelength dispersive X-ray spectrometer (WDXRF). Developed by ASTM International, this standard outlines the essential components of a wavelength dispersive X-ray spectrometer, enabling users to gain a clear understanding of the system’s structure and performance. The document is especially valuable for laboratories and manufacturers seeking to evaluate, compare, and specify WDXRF instruments or to collaborate in developing analytical methods tailored to specific analytical requirements.

Key Topics

• Core Components: The standard identifies the critical hardware and configurations, including sequential, simultaneous, and hybrid spectrometers, as well as key optical and detection elements.
• Spectrometer Environment: Considerations such as temperature control, vacuum or helium optical paths, and specimen chamber design are discussed as they affect instrument stability and performance.
• Excitation and Detection: Details the types and operating principles of X-ray tubes, high voltage generators, detectors (such as proportional and scintillation counters), and beam moderating devices.
• Sample Handling: Outlines requirements for specimen holders, changers, rotation mechanisms, and surface preparation, which impact the accuracy and repeatability of results.
• Dispersion and Optics: Specifies requirements for analyzing crystals and monochromators for wavelength dispersion, as well as the role of slits, apertures, and filters in optimizing measurements.
• Signal Processing and Software: Explains the function of preamplifiers, amplifiers, pulse height discriminators, and the importance of robust data acquisition, calibration, and analytical software.
• Performance Criteria: Provides guidance on assessing detector linearity, precision, and detection limits in X-ray spectrometry.
• Safety Features: Describes minimum requirements for user safety, including interlocks, emergency shutdown systems, and “X-Rays On” indicators.

Applications

Wavelength dispersive X-ray spectrometers described in ASTM E1172-22 are widely used in:

• Materials Analysis: Quantitative and qualitative elemental analysis of metals, ores, ceramics, and other materials in industrial, research, and quality control settings.
• Alloy and Matrix Characterization: Accurate determination of alloy compositions by analyzing multiple component elements and their mass fractions.
• Process Control: Monitoring and controlling product quality in metallurgical and mining industries using rapid and reliable X-ray fluorescence analysis.
• Laboratory Collaboration: Facilitating communication between laboratories and instrument manufacturers for developing customized, application-specific analytical methods.

Laboratories implementing this standard are advised to clearly understand their analytical requirements (alloy types, elements, detection limits) and to communicate these needs to manufacturers. This collaboration ensures that chosen instrument configurations and software solutions meet performance expectations and regulatory requirements.

Related Standards

ASTM E1172-22 references several key standards for supplementary guidance:

• ASTM E135 – Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• ASTM E2857 – Guide for Validating Analytical Methods

Additionally, compliance with recognized international standardization principles, such as those set by the WTO Technical Barriers to Trade (TBT) Committee, reinforces the global applicability of ASTM E1172.

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By providing a systematic approach to the specification and comparison of wavelength dispersive X-ray spectrometers, ASTM E1172-22 helps ensure optimized instrument performance, safety, and method development for a wide range of analytical applications. For more information or to obtain the full standard, visit the ASTM International website.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1172 − 22
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 presented so that the user may gain a general understanding of
the structure of an X-ray spectrometer system. It also provides
1.1 This practice covers the components of a wavelength
ameansforcomparingandevaluatingdifferentsystemsaswell
dispersive X-ray spectrometer that are basic to its operation
as understanding the capabilities and limitations of each
and to the quality of its performance. It is not the intent of this
instrument.
practice to specify component tolerances or performance
criteria, as these are unique for each instrument. However, the
4.2 A laboratory may implement this practice or an X-ray
practice does attempt to identify which tolerances are critical
fluorescence method in partnership with a manufacturer of the
and thus which should be specified.
analytical instrumentation. If a laboratory chooses to consult
1.2 This standard does not purport to address all of the
with an instrument manufacturer, then the following should be
safety concerns, if any, associated with its use. It is the
considered. The laboratory should know the alloy matrices to
responsibility of the user of this standard to establish appro-
be analyzed, elements and mass fraction ranges to be
priate safety, health, and environmental practices and deter-
determined, and the expected performance requirements for
mine the applicability of regulatory limitations prior to use.
each of these elements. The laboratory should inform the
Specific safety hazard statements are given in Section 7.
instrument manufacturer of these requirements so an analytical
1.3 This international standard was developed in accor-
method may be developed which meets the laboratory’s
dance with internationally recognized principles on standard-
expectations. Typically, instrument manufacturers customize
ization established in the Decision on Principles for the
the instrument configuration to satisfy the end-user’s require-
Development of International Standards, Guides and Recom-
ments for elemental coverage, elemental precision, and detec-
mendations issued by the World Trade Organization Technical
tion limits. Instrument manufacturer developed analytical
Barriers to Trade (TBT) Committee.
methods may include specific parameters for sample
excitation, wavelengths, inter-element interference corrections,
2. Referenced Documents
calibration and regression, equipment configuration/
2.1 ASTM Standards:
installation,andsamplepreparationrequirements.Laboratories
E135 Terminology Relating to Analytical Chemistry for
shouldhaveabasicunderstandingoftheparametersderivedby
Metals, Ores, and Related Materials
the manufacturer.
E2857 Guide for Validating Analytical Methods
3. Terminology
5. Description of Equipment
3.1 For definitions of terms used in this practice, refer to
5.1 Types of Spectrometers—X-ray spectrometers can be
Terminology E135.
classified as sequential, simultaneous, or hybrid (see 5.1.3).
4. Significance and Use
5.1.1 Sequential Spectrometers—The sequential spectrom-
eter disperses and detects secondary X-rays by means of an
4.1 This practice describes the essential components of a
adjustable monochromator called a goniometer. Secondary
wavelength dispersive X-ray spectrometer. This description is
X-rays emitted from the specimen pass through a mask that
defines the viewed region of the specimen. These X-rays enter
This practice is under the jurisdiction of ASTM Committee E01 on Analytical
Chemistry for Metals, Ores, and Related Materials and is the direct responsibility of
a collimator, typically a Soller slit, and nonparallel X-rays are
Subcommittee E01.20 on Fundamental Practices.
eliminated by being absorbed by the blades of the collimator.
Current edition approved Dec. 1, 2022. Published January 2023. Originally
The parallel beam of X-rays impinge an analyzing crystal that
approved in 1987. Last previous edition approved in 2016 as E1172 – 16. DOI:
10.1520/E1172-22.
disperses the X-rays according to their wavelengths. The
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
dispersed X-rays are measured by suitable detectors, which
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
may have an attached collimator in front of the entrance
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. window. Adjustment of the goniometer changes the angle
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1172 − 22
between the specimen, crystal, and detector, permitting the permits the window of the X-ray tube to be thinner and thus
measurement of different wavelengths, and therefore, different affords more efficient transmittance of longer wavelengths.
elements.
5.3.1.1 X-ray tubes are produced with a variety of targets.
5.1.2 Simultaneous Spectrometers—Simultaneous spec- The choice of the target material depends upon the wave-
trometers use multiple monochromators to measure a selected lengths that require excitation. X-rays from certain materials
wavelength of X- rays for each element. A typical monochro- excite longer wavelengths more efficiently. Other materials are
mator consists of an entrance slit, a curved (focusing) analyz- better for exciting shorter wavelengths. Generally the choice of
ing crystal, an exit slit, and a suitable detector. Secondary target material is a compromise.
X-rays pass through the entrance slit and impinge on the
5.3.1.2 X-ray tubes are rated according to maximum
analyzing crystal, which diffracts the wavelength of interest
voltage, maximum current, and typical power settings. These
and focuses it through the exit slit to enter the detector. Some
should be specified by the manufacturer.
simultaneous instruments use flat crystals.
5.3.2 High Voltage Generator—The high voltage generator
5.1.3 Hybrid Spectrometers—Hybrid spectrometers com-
supplies power to the X-ray tube. Its stability is critical to the
bine features found in sequential and simultaneous instru-
precision of the instrument.
ments. One type uses a set of fixed monochromators for key
5.3.2.1 The dc voltage output of the high voltage generator
X-ray lines and a goniometer for choosing other lines.Another
is typically adjustable within the range of 20 kV to 60 kV.
type uses a set of fixed monochromators along with an energy
Some designs operate at lower voltage and some provide up to
dispersive device for choosing other lines.
100 kV. Voltage stability, thermal drift, and voltage ripple
should be specified. Voltage repeatability should be specified
5.2 Spectrometer Environment:
for a programmable generator.
5.2.1 Temperature Stabilization—A means for stabilizing
5.3.2.2 The current to the X-ray tube is typically adjustable
the temperature of the spectrometer should be provided. The
from 5 mA to 125 mA, with some generators rated up to 160
degree of temperature control should be specified by the
mA. Current stability and thermal drift should be specified.
manufacturer. Temperature stability directly affects instrument
Current repeatability should be specified for programmable
stability.
generators.
5.2.2 Optical Path:
5.3.2.3 Voltage and current recovery times should be speci-
5.2.2.1 A vacuum path is generally preferred, especially
fiedforprogrammablegenerators.Thesoftwareroutineswhich
when measuring X-rays of low energy (long wavelengths) that
control the generator must delay measurement until the gen-
areabsorbedbyairornitrogen.Instrumentscapableofvacuum
erator recovers from voltage or current changes.
operation should have a vacuum gauge to indicate vacuum
5.3.2.4 Input power requirements should be specified by the
level. An airlock mechanism should be provided to evacuate
manufacturer so the proper power can be supplied when the
the specimen chamber before opening it to the spectrometer.A
instrument is installed. Maximum generator power output
means of controlling evacuation time is a desirable feature.
should be stated.
5.2.2.2 A helium path is recommended when measurement
5.3.3 Cooling Requirements—The X-ray tube and some
of low energy X-rays is required and the specimen (such as a
high voltage generators require cooling by either filtered tap
liquid) would be negatively affected by a vacuum. Instruments
water or a closed-loop heat exchanger system.
equipped for helium operation should have an airlock for
flushing the specimen chamber with helium before introducing
5.3.3.1 The manufacturer should specify water flow and
the specimen into the spectrometer. A means of controlling
quality requirements.
helium flush time is a desirable feature. The manufacturer
5.3.3.2 To protect components from overheating, an inter-
should also provide a means for accurately controlling the
lock circuit that monitors either water coolant flow or tempera-
pressure of the helium within the spectrometer.
ture or both should shut down power to the X-ray tube
5.2.2.3 Operation with air in the optical path may be an
whenever these requirements are not met.
option with some spectrometer designs.
5.3.3.3 Water purity is especially critical in cathode-
grounded systems because the coolant must be nonconducting.
NOTE 1—Some spectrometers prevent operation in air because high
A closed-loop heat exchanger is necessary to supply high
X-ray flux generates ozone that damages elastomers in vacuum seals.
Some spectrometers use bellows coupled to micro-switches as safety purity, low conductivity water. A conductivity gauge may be
interlocks to prevent users from being exposed to X-rays and to prevent
provided to protect the X-ray tube when conductivity becomes
damage resulting from operation with an air-filled optical path.
too high. The closed loop may incorporate an ion exchange
resin to maintain water purity.
5.3 Excitation—A specimen is excited by X-rays generated
by an X-ray tube powered by a high voltage generator. The
5.3.4 Primary Beam Filter—A primary beam filter is com-
wavelength distribution and flux of X-rays striking the speci-
monly used in sequential spectrometers to filter out character-
men is varied by changing the power settings to the tube or by
istic emissions from the X-ray tube target when these emis-
inserting filters into the beam path between the tube window
sions might interfere with measurement of an analyte element.
and the specimen position.
Primarybeamfiltersarealsousefulforloweringbackgroundin
5.3.1 X-Ray Tube—TheX-raytubemaybeoneoftwotypes: the longer wavelength (lower energy) portion of the spectrum.
end-window or side-window. Depending upon the instrument, This serves to increase the peak to background ratio and to
eithertheanodeorthecathodeisgrounded.Cathodegrounding lower detection limits.
E1172 − 22
5.3.4.1 Primary beam filters are made of several different specimen and the analyzing crystal. Auxiliary slits may be
metals (depending upon the X-ray tube target) and come in a installed at the detector windows between the detector and the
variety of thicknesses. The manufacturer should specify the analyzing crystal.
type, thickness, and location of the primary beam filter. 5.6.1.2 It is common for a sequential spectrometer to have a
selection of Soller slits with different blade spacing mounted in
5.4 Sample Positioning—Theprocessofpositioningaspeci-
a changer mechanism. Better resolution is achieved with closer
men for measurement in a spectrometer involves several
blade spacing, but at the expense of a loss of signal intensity.
components: the specimen holder, the specimen changer, and
5.6.1.3 The manufacturer should specify the location and
the specimen rotation mechanism (spinner).These components
plate spacing of all Soller slits installed in a particular
contribute collectively to the repeatability of positioning the
instrument.
specimen in the optical path and thus to instrument precision.
5.6.2 Entrance and Exit Slits—Both entrance and exit slits
5.4.1 If provided, a spinner rotates the specimen while it is
are required in a curved-crystal spectrometer. The curved
being exposed to the primary X-ray beam, helping to minimize
crystal establishes a focusing circle that is similar to the
the influence of surface preparation striations or defects and
Rowland circle defined by a grating in an atomic emission
specimen heterogeneity on analytical results. Specimen rota-
spectrometer. In contrast, proper focusing in an X-ray fluores-
tion rate should be specified by the manufacturer.
cence spectrometer requires that both slits not only be on the
5.4.2 The condition of the surface of a specimen has the
focusing circle but also have identical chordal distances from
greatest effect on analytical results in spectrometers having a
theslitstothecrystal.Adetectorisaimedatthecrystalthrough
shallow angle of incidence of primary X-rays with respect to
the exit slit.
the specimen surface or a shallow angle of viewing the
5.6.2.1 The manufacturer should specify the sizes of the
...

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. Because
it may 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 version
of the standard as published by ASTM is to be considered the official document.
Designation: E1172 − 16 E1172 − 22
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
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. However, the practice does attempt to identify which 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 responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and to 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 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
E135 Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
E2857 Guide for Validating Analytical Methods
3. Terminology
3.1 For terminology relating to X-ray spectrometry, definitions of terms used in this practice, refer to Terminology E135.
4. Significance and Use
4.1 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 cursorygeneral 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.
This practice is under the jurisdiction of ASTM Committee E01 on Analytical Chemistry for Metals, Ores, and Related Materials and is the direct responsibility of
Subcommittee E01.20 on Fundamental Practices.
Current edition approved June 1, 2016Dec. 1, 2022. Published June 2016January 2023. Originally approved in 1987. Last previous edition approved in 20112016 as
E1172 – 87E1172 – 16.(2011). DOI: 10.1520/E1172-16.10.1520/E1172-22.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1172 − 22
4.2 It is understood that a A laboratory may implement this practice or an X-ray fluorescence method in partnership with a
manufacturer of the analytical instrumentation. If a laboratory chooses to consult with an instrument manufacturer, then the
following should be considered. The laboratory should have an idea of know the alloy matrices to be analyzed, elements and mass
fraction ranges to be determined, and the expected performance requirements for each of these elements. The laboratory should
inform the instrument manufacturer of these requirements so they may develop an analytical method may be developed which
meets the laboratory’s expectations. Typically, instrument manufacturers customize the instrument configuration to satisfy the
end-user’s requirements for elemental coverage, elemental precision, and detection limits. Instrument manufacturer developed
analytical methods may include specific 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 the parameters derived by the manufacturer.
5. Description of Equipment
5.1 Types of Spectrometers—X-ray spectrometers can be classified as sequential, simultaneous, or hybrid (see 5.1.3).
5.1.1 Sequential Spectrometers—The sequential spectrometer disperses and detects secondary X-rays by means of an adjustable
monochromator called a goniometer. Secondary X-rays emitted from the specimen pass through a mask that defines the viewed
region of the specimen. Next, theyThese X-rays enter a collimator, typically a Soller slit, and nonparallel X-rays are eliminated
by being absorbed by the blades of the collimator. The parallel beam of X-rays strikesimpinge an analyzing crystal that disperses
the X-rays according to their wavelengths. The dispersed X-rays are measured by suitable detectors, which may have an attached
collimator in front of the entrance window. Adjustment of the goniometer changes the angle between the specimen, crystal, and
detector, permitting the measurement of different wavelengths, and therefore, of different elements.
5.1.2 Simultaneous Spectrometers—Simultaneous spectrometers use an individual monochromator multiple monochromators to
measure a selected wavelength of X- rays for each element. A typical monochromator consists of an entrance slit, a curved
(focusing) analyzing crystal, an exit slit, and a suitable detector. Secondary X-rays pass through the entrance slit and strike impinge
on the analyzing crystal, which diffracts the wavelength of interest and focuses it through the exit slit to enter the detector. Some
simultaneous instruments use flat crystals.
5.1.3 Hybrid Spectrometers—Hybrid spectrometers combine features found in sequential and simultaneous instruments. One type
uses a set of fixed monochromators for key X-ray lines and a goniometer for choosing other lines. Another type uses a set of fixed
monochromators along with an energy dispersive device for choosing other lines.
5.2 Spectrometer Environment:
5.2.1 Temperature Stabilization—A means for stabilizing the temperature of the spectrometer should be provided. The degree of
temperature control should be specified by the manufacturer. Temperature stability directly affects instrument stability.
5.2.2 Optical Path:
5.2.2.1 A vacuum path is generally preferred, especially for the measurement of when measuring X-rays of sufficiently low energy
(long wavelengths) to bethat are absorbed by air or nitrogen. Instruments capable of vacuum operation should have a vacuum
gauge to indicate vacuum level. An airlock mechanism should be provided to evacuate the specimen chamber before opening it
to the spectrometer. A means of controlling evacuation time is a desirable feature.
5.2.2.2 A helium path is recommended when measurement of low energy X-rays is required and the specimen (such as a liquid)
would be disturbed negatively affected by a vacuum. Instruments equipped for helium operation should have an airlock for flushing
the specimen chamber with helium before introducing the specimen into the spectrometer. A means of controlling helium flush time
is a desirable feature. The manufacturer should also provide a means for accurately controlling the pressure of the helium within
the spectrometer.
5.2.2.3 Operation with air in the optical path may be an option with some spectrometer designs.
NOTE 1—Some spectrometers do not allow prevent operation in air because high X-ray flux generates ozone that damages elastomers in vacuum seals.
Some spectrometers use bellows coupled to micro-switches as the safety interlockinterlocks to prevent accidental exposure to X-rays by those repairing
a spectrometer users from being exposed to X-rays and to prevent damage resulting from operation with an air-filled optical path.
E1172 − 22
5.3 Excitation—A specimen is excited by X-rays generated by an X-ray tube powered by a high voltage generator. The wavelength
distribution and flux of X-rays striking the specimen is varied by changing the power settings to the tube or by inserting filters into
the beam path between the tube window and the specimen position.
5.3.1 X-Ray Tube—The X-ray tube may be one of two types: end-window or side-window. Depending upon the instrument, either
the anode or the cathode is grounded. Cathode grounding permits the window of the X-ray tube to be thinner and thus affords more
efficient transmittance of longer wavelengths.
5.3.1.1 X-ray tubes are produced with a variety of targets. The choice of the target material depends upon the wavelengths that
require excitation. X-rays from certain materials excite longer wavelengths more efficiently. Other materials are better for exciting
shorter wavelengths. Generally the choice of target material is a compromise.
5.3.1.2 X-ray tubes are rated according to maximum power,voltage, maximum current, and typical power settings. These should
be specified by the manufacturer.
5.3.2 High Voltage Generator—The high voltage generator supplies power to the X-ray tube. Its stability is critical to the precision
of the instrument.
5.3.2.1 The dc voltage output of the high voltage generator is typically adjustable within the range of 20 kV to 60 kV. Some
designs operate at lower voltage and some provide up to 100 kV. Voltage stability, thermal drift, and voltage ripple should be
specified. Voltage repeatability should be specified for a programmable generator.
5.3.2.2 The current to the X-ray tube is typically adjustable within the range of from 5 mA to 125 mA, with some
suppliesgenerators rated up to 160 mA. Current stability and thermal drift should be specified. Current repeatability should be
specified for programmable generators.
5.3.2.3 Voltage and current recovery times should be specified for programmable generators. The software routines which control
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 the
instrument is installed. Maximum generator power output should be stated.
5.3.3 Cooling Requirements—The X-ray tube and some high voltage generators require cooling by either filtered tap water or a
closed-loop heat exchanger system.
5.3.3.1 The manufacturer should 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 or both
should shut down power to the X-ray tube whenever these requirements are not met.
5.3.3.3 Water purity is especially critical in cathode-grounded systems because the coolant must be nonconducting. A closed-loop
heat exchanger is necessary to supply high purity, low conductivity water. A conductivity gauge may be provided to protect the
X-ray tube when conductivity becomes too high. The closed loop may incorporate an ion exchange resin to maintain water purity.
5.3.4 Primary Beam Filter—A primary beam filter is commonly used in sequential spectrometers to filter out characteristic
emissions from the X-ray tube target when these emissions might interfere with measurement of an analyte element. Primary beam
filters are also useful for lowering background in the longer wavelength (lower energy) portion of the spectrum. This serves to
increase the peak to background ratio and to lower detection limits.
5.3.4.1 Primary beam filters are made of several different metals (depending upon the X-ray tube target) and come in a variety
of thicknesses. The manufacturer should specify the type, thickness, and location of the primary beam filter.
5.4 Sample Positioning—The process of positioning a specimen for measurement in a spectrometer involves several components:
the specimen holder, the specimen changer, and the specimen rotation mechanism (spinner). These components contribute
collectively to the repeatability of positioning the specimen in the optical path and thus to instrument precision.
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5.4.1 If provided, a spinner rotates the specimen while it is being exposed to the primary X-ray beam, helping to minimize the
influence of surface preparation striations or defects and specimen heterogeneity on analytical results. Specimen rotation rate
should be specified by the manufacturer.
5.4.2 Imperfections in The condition of the surface of a specimen havehas the greatest effect on analytical results in spectrometers
having a shallow angle of incidence of primary X-rays with respect to the specimen surface or a shallow angle of viewing the
secondary X-rays with respect to the specimen surface, or both. The manufacturer should specify these angles.
5.4.3 Maximum Minimum and maximum specimen size (thickness and diameter) should be specified.
5.5 Dispersion—The analyzing crystal is the dispersive device in a wavelength dispersive X-ray spectrometer. A number of
crystals providing a range of interplanar spacings are used to disperse the secondary X-rays.
5.5.1 Sequential spectrometers may contain several different crystals mounted on a changer mechanism to allow the analystuser
to select a specific crystal for the wavelength being measured. Crystals of similar lattice spacing, but different composition, may
offer significantly different reflection efficiency.
5.5.2 Each monochromator in a simultaneous instrument has a specified crystal selected in accordance with the expected analytical
requirements. The crystal is generally bent and ground to a curve or a logarithmic spiral to focus the diffracted X-rays through the
monochromator’s
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