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Philips PW2404 X-ray Fluorescence Spectrometer
with Super Q Software
Purchased with a grant from the National Science Foundation
What it does:
X-ray fluorescence provides
accurate quantitative data on the chemical composition of geologic samples.
Instrument and Analytical Statistics:
Samples for major element analysis are
powdered and mixed with lithium tetraborate flux in a 9:1 flux:sample ratio, then
melted to produce a glass disc using a Claisse Fluxy Fluxer. For trace element analysis, powered samples are
mixed in approximately a 5:1 sample:flux ratio with Copolywax flux, then formed into
a pressed pellet using an hydraulic press. Major element calibration curves are based
on a set of 40 standards. A set of 30 standards is used for trace element analyses.
How it works:
Each chemical element is composed of
a nucleus along with a specific number of orbiting electrons. During x-ray fluorescence
analysis, high energy x-ray photons produced in the x-ray tube bombarb the sample
causing the ejection of electrons from their orbitals. Fluorescence occurs when
energy is given off as outer shell electrons drop down to replace inner shell
electrons that have been ejected. The amount of energy lost as a result of each
such electron transition, along with its related wavelength, are specific to each
particular element.
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Within the x-ray spectrometer, a crystal with a known lattice
spacing is used as a diffraction grating that allows through only one x-ray wavelength
at any given diffraction angle. Because the x-ray wavelengths produced by fluorescence
are unique to each element, this diffraction restricts all energy except for that of the
element of interest from reaching the detector. Therefore, any signal that is picked
up by the detector can be attributed to the element of interest. The more there is of
that element in a sample, the more electron transitions that can occur, and the more
signal that will be produced. The amount of signal that is received is compared
to calibration curves, which are plots of the amount of energy received vs. weight
percent for standards with known compositions.
Related Research:
This system has been used extensively
to collect data for a wide variety research. Some of the major projects include:
- CZEN - Critical Zone research on soil development & chemical weathering (Project Website)
- NSF/CRUI - Study on Acid Deposition and Calcium Depletion in Adirondack Soils
- ILWAS - Integrated Lake Watershed Acidification Study - a study of the effects of acid deposition on three Adirondack lakes
- RILWAS - Regional Integrated Lake Watershed Acidification Study - a study of the effects of acid deposition on lakes in
the Adirondacks and various other locations across the United States, Canada, and Europe
- ALBIOS - Aluminum Biogeochemstry Study - a study of the effects of aluminum on forested ecosystems
- IFS - Integrated Forest Study - an international effort to study the effects of acid deposition on forest ecosystems throughout
the U.S., Canada, and Europe
Last updated 2/12
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