ANALYTICAL METHODS/Geochemical Analysis (Including X-ray) 61 Figure General set of processes involved in the generation of fluorescent X rays by X ray bombardment of atoms The small grey filled circle represents the nucleus; the outer rings represent electron orbitals The thicker black circle represents the location of a given electron (e ) With X ray bombardment, the highlighted electron jumps to a higher orbital The energized electron quickly falls back to its original state, releasing a secondary X ray The range of elements in a sample leads to a range of characteristic fluorescent X rays with peak heights that are functions of the amounts of the elements in the sample tube or even a radioactive source) strikes a sample, the X-ray can be either absorbed by the atom or scattered through the material Some incident X-rays are absorbed by the atom, and electrons are ejected from the inner shells to outer shells, creating vacancies As the atom returns to its stable condition, electrons from the outer shells are transferred to the inner shells and in the process give off a characteristic X-ray with an energy equal to the difference between the two binding energies of the corresponding shells XRF is widely used to measure the elemental composition of natural materials, since it is fast and nondestructive to the sample It can be used to measure many elements simultaneously XRF can be used directly on rock surfaces, although there is a danger of natural heterogeneity resulting in variable results Rock, soil, and sediment samples are typically crushed and made into pellets by compressing them or by melting the whole sample and then quenching to make a glass disk XRF is useful for the geochemical analysis of a wide range of metals and refractory and amphoteric compounds (such as SiO2 and Al2O3) and even some non-metals (chloride and bromide) XRF is also routinely used to measure the natural metal content of liquid petroleum samples The quality of XRF data is a function of the selection of appropriate standards It is considered to be best practice to use standards that are similar to the samples in question to minimize matrix effects XRF can measure down to parts-per-million concentrations and lower, depending on the element and the material X-ray Diffraction X-rays have a similar wavelength to the lattice spacing of common rock-forming minerals and have been used to characterize the crystal structure and mineralogy of Earth materials by using X-ray diffraction (XRD) analysis This is most commonly used to define the presence of minerals, mineral proportions, mineral composition (in favourable circumstances), and other subtle mineralogical features of rocks, sediments, and soils X-rays, even from a pure elemental source bombarded with electrons, have a collection of peaks – X-rays characteristic of the quantized electron energy levels – and bremsstrahlung X-ray beams of a tightly defined energy (and thus wavelength) have been used to investigate and characterize the minerals present in rocks, sediments, and soils by removing all but one X-ray peak from the spectrum of wavelengths generated by a source element X-rays are useful in investigating mineral structure since they can be selected to have a wavelength that is only just smaller than the interlattice spacing (d-spacing) of common rockforming minerals A number of X-ray sources have historically been selected, but copper is the most commonly employed, and the copper Ka peak is the one that is directed onto samples This has a charac˚ (0.15418 nm) This is teristic wavelength of 1.5418 A ideal for many minerals since they have high-order (dominant, most obvious) lattice spacings of this size or up to 10–15 times greater than this wavelength