What it does: X-ray fluorescence provides accurate quantitative data on the chemical composition of geologic samples.

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.
    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.

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. 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.

Related Research: This system has been used extensively to collect data for a wide variety research. Some of the major projects include:

• 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