General Materials
ID #1020
X-Ray Spectrometry,X-Ray Emission
General Uses
· Nondestructive multielemental analysis of thin samples, sodium through uranium, to approximately 1
ppm or 10-9 g/cm2
· Nondestructive multielemental analysis of thick samples for medium and heavy elements
· Semiquantitative analysis of elements versus depth
· Elemental analyses of large and/or fragile objects through external beam proton milliprobe
· Elemental analyses using proton microprobes, spatial resolution to a few microns, and mass detection
limits below 10-16 g
Examples of Applications
· Analysis of air filters for a wide range of elements
· Analysis of atmospheric aerosols by particle size for source transport, removal, and effect studies
· Analysis of powdered plant materials and geological powders for broad elemental content
· Analysis of elemental content of waters, solute, and particulate phases, including suspended particles
· Medical analysis for elemental content, including toxicology and epidemeology
· Analysis of materials for the semiconductor industry and for coating technology
· Archaeological and historical studies of books and artifacts, often using external beams
· Forensic studies
Samples
· Form: Thin samples (generally no more than a 10-mg/cm2 thick solid) are analyzed in vacuum, as are
stabilized powders and evaporated fluids. Thick samples can be any solid and thickness, but proton
beam penetration is typically 30 mg/cm2 or approximately 0.15 mm (0.006 in.) in a geological sample
· Size: The sample area analyzed is on the order of millimeters to centimeters, except in microprobes, in
which beam spot sizes approaching 1 μm are available
· Preparation: None for air filters and many materials. Powders and liquids must be stabilized, dried, and
generally placed on a substrate, such as plastic. Thick samples can be pelletized
Limitations
· Access to an ion accelerator of a few mega electron volts is necessary
· Generally, no elements below sodium are quantified
· Elements must be present above approximately 1 ppm
· Sample damage is more likely than with some alternate methods
· No chemical information is generated
· Computer codes are necessary for large numbers of analyses
Estimated Analysis Time
· 30 s to 5 min in most cases; thousands of samples can be handled in a few days
Capabilities of Related Techniques
· X-ray fluorescence: With repeated analyses at different excitation energies, essentially equivalent or
somewhat superior results can be obtained when sample size and mass are sufficient · Neutron activation analysis: Variable elemental sensitivity to neutron trace levels for some elements,
essentially none for other elements. Neutron activation analysis is generally best for detecting the least
common elements, but performs the poorest on the most common elements, complementing x-ray
techniques
· Electron microprobe: Excellent spatial resolution (approximately 1 μm), but elemental mass sensitivity
only approximately one part per thousand
· Optical methods: Atomic absorption or emission spectroscopy, for example, are generally applicable to
elements capable of being dissolved or dispersed for introduction into a plasma.
Introduction
Particle-induced x-ray emission (PIXE) is one of several elemental analyses based on characteristic x-rays. These
methods can be classified by the method of excitation and the nature of x-ray detection. The excitation source creates
inner electron shell atomic vacancies that cause x-ray emission when filled by outer electrons. X-ray fluorescence (XRF)
uses x-rays for this purpose; electrons are used to cause vacancies in electron microprobes and some scanning electron
microscopes. Particle-induced x-ray emission uses beams of energetic ions, normally protons of a few mega electron
volts, to create inner electron shell vacancies. Regarding detection, the most widely used methods involve wavelength
dispersion, which is scattering from a crystal, or energy dispersion, which involves direct conversion of x-ray energy into
electronic pulses in silicon or germanium diodes.
These methods all provide quantitative analyses of elemental content, yet the differences between PIXE and other x-raybased
methods have favored PIXE in several specialized analytical applications, especially environmental and biological.
Recent developments in focusing energetic proton beams (proton microprobes) have expanded the utility of PIXE in
applications in geology and materials science, combining part per million elemental sensitivity and micron spatial
resolution.
· Nondestructive multielemental analysis of thin samples, sodium through uranium, to approximately 1
ppm or 10-9 g/cm2
· Nondestructive multielemental analysis of thick samples for medium and heavy elements
· Semiquantitative analysis of elements versus depth
· Elemental analyses of large and/or fragile objects through external beam proton milliprobe
· Elemental analyses using proton microprobes, spatial resolution to a few microns, and mass detection
limits below 10-16 g
Examples of Applications
· Analysis of air filters for a wide range of elements
· Analysis of atmospheric aerosols by particle size for source transport, removal, and effect studies
· Analysis of powdered plant materials and geological powders for broad elemental content
· Analysis of elemental content of waters, solute, and particulate phases, including suspended particles
· Medical analysis for elemental content, including toxicology and epidemeology
· Analysis of materials for the semiconductor industry and for coating technology
· Archaeological and historical studies of books and artifacts, often using external beams
· Forensic studies
Samples
· Form: Thin samples (generally no more than a 10-mg/cm2 thick solid) are analyzed in vacuum, as are
stabilized powders and evaporated fluids. Thick samples can be any solid and thickness, but proton
beam penetration is typically 30 mg/cm2 or approximately 0.15 mm (0.006 in.) in a geological sample
· Size: The sample area analyzed is on the order of millimeters to centimeters, except in microprobes, in
which beam spot sizes approaching 1 μm are available
· Preparation: None for air filters and many materials. Powders and liquids must be stabilized, dried, and
generally placed on a substrate, such as plastic. Thick samples can be pelletized
Limitations
· Access to an ion accelerator of a few mega electron volts is necessary
· Generally, no elements below sodium are quantified
· Elements must be present above approximately 1 ppm
· Sample damage is more likely than with some alternate methods
· No chemical information is generated
· Computer codes are necessary for large numbers of analyses
Estimated Analysis Time
· 30 s to 5 min in most cases; thousands of samples can be handled in a few days
Capabilities of Related Techniques
· X-ray fluorescence: With repeated analyses at different excitation energies, essentially equivalent or
somewhat superior results can be obtained when sample size and mass are sufficient · Neutron activation analysis: Variable elemental sensitivity to neutron trace levels for some elements,
essentially none for other elements. Neutron activation analysis is generally best for detecting the least
common elements, but performs the poorest on the most common elements, complementing x-ray
techniques
· Electron microprobe: Excellent spatial resolution (approximately 1 μm), but elemental mass sensitivity
only approximately one part per thousand
· Optical methods: Atomic absorption or emission spectroscopy, for example, are generally applicable to
elements capable of being dissolved or dispersed for introduction into a plasma.
Introduction
Particle-induced x-ray emission (PIXE) is one of several elemental analyses based on characteristic x-rays. These
methods can be classified by the method of excitation and the nature of x-ray detection. The excitation source creates
inner electron shell atomic vacancies that cause x-ray emission when filled by outer electrons. X-ray fluorescence (XRF)
uses x-rays for this purpose; electrons are used to cause vacancies in electron microprobes and some scanning electron
microscopes. Particle-induced x-ray emission uses beams of energetic ions, normally protons of a few mega electron
volts, to create inner electron shell vacancies. Regarding detection, the most widely used methods involve wavelength
dispersion, which is scattering from a crystal, or energy dispersion, which involves direct conversion of x-ray energy into
electronic pulses in silicon or germanium diodes.
These methods all provide quantitative analyses of elemental content, yet the differences between PIXE and other x-raybased
methods have favored PIXE in several specialized analytical applications, especially environmental and biological.
Recent developments in focusing energetic proton beams (proton microprobes) have expanded the utility of PIXE in
applications in geology and materials science, combining part per million elemental sensitivity and micron spatial
resolution.
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Last update: 2008-03-25 20:56
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