Arriving Equipment

EPA has purchased new pieces of equipment to give researchers the ability to conduct increasingly advanced studies in their effort to improve the health of the public and the environment:

X-Ray Diffractometer (XRD)

X-ray diffraction is a versatile, nondestructive technique used for identifying the crystalline phases present in solid materials and powders. It is also used for analyzing structural properties (such as stress, grain size, phase composition, crystal orientation, and defects) of the phases. The technique uses a beam of X-rays to bombard a specimen from various angles. The X-rays are diffracted (according to Bragg's law, which confirmed the existence of real particles at the atomic scale) as they are reflected from successive planes formed by the crystal lattice of the material. By varying the angle of incidence, a diffraction pattern emerges that is characteristic of the sample. The pattern is identified by comparing it with tens of thousands of reference patterns contained in an internationally recognized database.

Estimated time of arrival: TBA

Scanning Transmission Electron Microscope (STEM)

With a scanning transmission electron microscope (STEM), the electron beam is raster-scanned across the material. (A raster scan is the pattern of image storage and transmission used in most computer image systems.) This produces a variety of electron and X-ray signals that may be used for compositional analysis.

The 200kV STEM operates at a resolution of .4 nanometers. It is used for examination of biological and material samples with similar applications to the transmission electron microscope but with the addition of a scan head that rasters the beam across the sample.

In one project, EPA will use the STEM systems to investigate the interactions between Pseudomonas aeruginosa (a soil bacterium found near an abandoned Kentucky lead mine) and heavy metals, including lead, arsenic, and cadmium.

In combination with an electron dispersive spectrometer system, the STEM system produces a variety of electron and X-ray signals that may be used for compositional analysis.

Estimated time of arrival: winter 2008

Arriving Equipment

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