ASTM C982-88(1997)e1
(Guide)Standard Guide for Selecting Components for Energy-Dispersive X-Ray Fluorescence (XRF) Systems
Standard Guide for Selecting Components for Energy-Dispersive X-Ray Fluorescence (XRF) Systems
SCOPE
1.1 This guide describes the components for an energy-dispersive X-ray fluorescence (XRF) system for materials analysis. It can be used as a reference in the apparatus section of test methods for energy-dispersive X-ray fluorescence analyses of nuclear materials.
1.2 The components recommended include X-ray detectors, signal processing electronics, data acquisition and analysis systems, and excitation sources that emit photons (See Fig. 1).
1.3 Detailed data analysis methods are not described or recommended, as they may be unique to a particular analysis problem. Some applications may require the use of spectrum deconvolution to separate partially resolved peaks or to correct for matrix effects in data reduction.
1.4 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.
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e1
Designation: C 982 – 88 (Reapproved 1997)
Standard Guide for Selecting Components for
Energy-Dispersive X-Ray Fluorescence (XRF) Systems
This standard is issued under the fixed designation C 982; 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 (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Keywords were added editorially in March 1998.
1. Scope using energy-dispersive XRF usually employ apparatus with
the components described in this document.
1.1 This guide describes the components for an energy-
dispersive X-ray fluorescence (XRF) system for materials
4. Hazards
analysis. It can be used as a reference in the apparatus section
4.1 XRF equipment analyzes by the interaction of ionizing
of test methods for energy-dispersive X-ray fluorescence
radiation with the sample. Applicable safety regulation and
analyses of nuclear materials.
standard operating procedures must be reviewed prior to the
1.2 The components recommended include X-ray detectors,
use of such equipment. (See NBS Handbook 111. )
signal processing electronics, data acquisition and analysis
4.2 Instrument performance may be influenced by environ-
systems, and excitation sources that emit photons (See Fig. 1).
mental factors such as heat, vibration, humidity, dust, stray
1.3 Detailed data analysis methods are not described or
electronic noise, and line voltage stability. These factors and
recommended, as they may be unique to a particular analysis
performance criteria should be reviewed with equipment
problem. Some applications may require the use of spectrum
manufacturers.
deconvolution to separate partially resolved peaks or to correct
4.3 The quality of quantitative XRF results can be depen-
for matrix effects in data reduction.
dent on a variety of factors, such as sample preparation and
1.4 This standard does not purport to address all of the
mounting. Consult the specific analysis method for recom-
safety problems, if any, associated with its use. It is the
mended procedures.
responsibility of the user of this standard to establish appro-
4.4 Sample chambers are available commercially for opera-
priate safety and health practices and determine the applica-
tion in air, vacuum, or helium atmospheres, depending upon
bility of regulatory limitations prior to use.
the elements to be determined and the physical form of the
2. Referenced Documents sample.
2.1 ASTM Standards:
5. Energy Dispersive X-Ray Detectors
E 135 Terminology Relating to Analytical Chemistry for
NOTE 1—Because of the rapid improvement in detector and electronics
Metals, Ores, and Related Materials
technologies, the most up-to-date information on XRF components is
E 181 General Methods for Detector Calibration and Analy-
found in manufacturers’ literature. Lists of vendors of XRF equipment can
sis of Radionuclides
be found in compilations such as the “Guide to Scientific Instruments,”
published by the American Association for the Advancement of Science,
3. Significance and Use
Washington, DC.
3.1 This guide describes typical prospective analytical
5.1 Energy-dispersive X-ray detectors can be used to detect
X-ray fluorescence systems that may be used for qualitative
X rays with energies from approximately 1 to 100 keV;
and quantitative elemental analysis of materials related to the
however, a single-type detector usually cannot satisfy all the
nuclear fuel cycle.
3.2 Standard methods for the determination of materials
General References for XRF include Bertin, Eugene P., Principles and
Practices of X-Ray Spectrometric Analysis, Second Ed., Plenum Press, New
York-London, 1975, Jenkins, Ron, An Introduction to X-Ray Spectrometry, Heyden
This guide is under the jurisdiction of ASTM Committee C-26 on Nuclear Fuel and Sons, Ltd., London, New York, Rhine, 1974, and Woldseth, Rolf, All You Ever
Cycle and is the direct responsibility of Subcommittee C26.05 on Methods of Test. Wanted to Know About X-Ray Energy Spectrometry, First Ed., Kevex Corporation,
Current edition approved Nov. 25, 1988. Published February 1989. Burlingame, CA, 1973.
2 5
Annual Book of ASTM Standards, Vol 03.05. Radiation Safety for X-Ray Diffraction and X-Ray Fluorescence Analysis
Annual Book of ASTM Standards, Vol 12.02. Equipment, National Institute of Standards and Technology, Washington, DC.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
C 982
Reprinted by permission of Kevex Corporation, Burlingame, CA.
FIG. 1 Function Block Diagram of XES System
requirements of efficiency and energy resolution over such a proportional counters, may be used in certain applications in
wide energy range. which the high resolution of the semiconductor detectors is not
5.2 The energy resolution (Terminology E 135) of a detector required.
is usually specified by the FWHM (full width at half maxi- 5.6 All types of X-ray detectors have entrance windows of
mum) of the full energy peak of an X ray (or g ray) of a a low-Z material (for example, Be on solid-state detectors or
particular energy and at a specified count rate. The FWTM (full plastic film on gas-filled counters) to minimize X-ray absorp-
width at one-tenth maximum) of the full-energy peak or the tion.
peak-to-background ratio, or both, may also be specified.
6. Signal Processing Electronics
“High resolution” (small values of FWHM) detectors are
6.1 The bias power supply required to operate X-ray detec-
required to separate X rays of similar energy emitted by
different elements. tors must be capable of delivering sufficient high voltage and
5.3 The dimension of the detector “active volume” is current for the particular detector. The power shall be regulated
usually specified for X-ray detection applications, allowing the and have ripple and noise content below the 10-mV level.
efficiency of the device for detecting a particular energy X ray 6.2 A preamplifier converts the charge pulse caused by an
to be estimated. ionizing event in the detector to a voltage signal. It must also
5.4 XRF analysis systems requiring high-resolution detec- minimize electronic noise that would degrade the spectrum
tors employ semiconductor (“solid state”) detectors. resolution. The preamplifier is typically charge sensitive and
5.4.1 Lithium-drifted silicon, Si(Li), detectors are usually uses a field-effect transistor. The noise content, gain, and
used for applications requiring the detection of X rays from 1 count-rate capability must be compatible with the particular
to 40 keV. Si(Li) resolution is commonly specified at 5.9 keV detector and application. “Resistive feedback” and “pulsed-
and 1000 cps. Resolutions of 145 to 160 eV (FWHM) are optical feedback” are two types of preamplifier techniques
typical. suitable for high-resolution spectroscopy. The preamplifier is
5.4.2 Germanium, Ge, detectors or lithium-drifted germa- usually supplied as an integral part of the detector, and the
nium, Ge(Li), detectors are usually employed to detect X rays detector manufacturer should be consulted to determine a
in the high-energy region of the X-ray spectrum. Ge resolution suitable preamplifier.
is commonly specified at 122 keV and 1000 cps when the 6.3 A shaping amplifier is used to integrate the preamplifier
detector is to be used for X-ray detection. Resolutions of 500 pulse for a well-defined duration, differentiate the pulse to
eV (FWHM) are typical. provide an acceptable shape, and amplify the pulse to an
appropriate voltage. Typical shaping times vary from 1 to 40 μs
5.4.3 Both Ge(Li) and Si(Li) detectors must be operated at
77°K (liquid nitrogen temperature). Si(Li) detectors can be depending on the detector count rate and the required energy
resolution. Amplifier outputs are approximately ten volts maxi-
stored at room temperature. Germanium detectors must be
stored at 77°K (Standard E 181). mum. The amplification factor is variable so that the output
5.4.4 Improvements in technology can extend the useful pulse height spectrum corresponds to the desired range of
energy range of a particular detector type or result in the X-ray energies. Most shaping amplifiers provide power to the
development of new detector materials. Manufacturers should preamplifier. High-resolution amplifiers are equipped with
be consulted for the latest information. adjustments for signal shaping to optimize the resolution at a
5.5 Scintillation detectors such as NaI(T1), or gas-filled given rate. Some high-resolution amplifiers are equipped with
N
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