The EDS detector uses a very sensitive semiconductor detector and separates elements on the basis of X-ray energies rather than wavelength (although these are related). The two new large crystal type spectrometers, give higher detection sensitivity for trace elements. The JXA-8230 has 5 WDS spectrometers, each with 2 different crystals, giving access to 76 elements from Be to U, excluding the rare gases and radioactive elements. In order to access different parts of the X-ray spectrum, several different crystals are required. By comparing the X-ray intensity of an element in a sample with the intensity in a reference material, the concentration of that element in the sample can be calculated. Wavelength dispersive spectrometers use a crystal monochromator to isolate a particular X-ray wavelength, characteristic of the energy transition of a certain element. The difference in energy between orbitals depends on the electronic configuration of the particular atom, and the X-ray photon wavelength is therefore characteristic of the element that produced it. An electron from an outer electron orbital can drop down to fill the space, and the difference in potential energy between the two states is released in the form of an X-ray photon. The incident electron beam can knock electrons out of orbitals around the nucleus of an atom in the sample and create an electron vacancy. X-ray analysis BSE image and WDS magnesium x-ray intensity map of a spicule They are also useful in identifying different mineral phases in a sample. The number of backscattered electrons is related to the mean atomic number under the beam, and BSE images can reveal subtle differences in mineral chemistry, such as crystal zoning. Backscattered electron images BSE image of clinopyroxene showing igneous zoningīackscattered electron (BSE) images are produced by counting the number of high energy electrons that are deflected from the surface of the sample. Secondary electron images however are superb for looking at fine scale details in various samples such as materials and microfossils. For polished surfaces, such as those used for X-ray analysis, these images show relatively little detail. In this mode, the instrument is equivalent to a scanning electron microscope (SEM), and is capable of taking high resolution images at a sub micron scale. Secondary electron images (SEI) are produced by collecting low energy electrons which are dislodged from the surface of a sample by the incident electron beam.
For more information please contact Ian Schipper: Electron imaging Secondary electron images SEI image of a flea We are currently implementing a limited semi-commercial service for EPMA analyses. The combined WD/ED system can simultaneously analyse up to 5 WDS elements and all EDS elements, as well as collecting BSE, SEI and CL images. Combined with a new PC-based operating environment, these allow the simultaneous collection of light, X-ray and electron signals. The instrument is a highly sensitive system featuring a combination of 5 wavelength dispersive X-ray spectrometers (WDS), a recently developed energy dispersive X-ray spectrometer (EDS) analyser featuring spectral imaging, a JEOL xCLent 3 cathodoluminescence (CL) spectrometer, and highly sensitive detectors for acquisition of backscattered electron (BSE) and secondary electron (SEI) images. Purchased in 2009, the EPMA is a key instrument in Victoria University of Wellington’s research programmes. Analysis of these phenomena can provide qualitative and quantitative information about the chemical composition of a sample, at a spatial resolution of less than 1 µm (0.001 mm).
The EPMA uses a focused beam of electrons to probe a solid sample, and interactions between the beam and the sample produce electrons, X-rays, and light.
JEOL JXA-8230 SuperProbe Electron Probe Microanalyser (EPMA)