Secondary x-ray emission

It is necessary in PIXE to take into account some correction factors for thickness evaluation due to X-ray absorption in the sample. In some samples (esp. in alloys) the influence of secondary X-ray emission should also be considered. 

It is also possible to create characteristic secondary X-ray emission using other incident radiation to excite the sample. When ions of suffident energy (usually MeV protons) produced by an ion accelerator are employed as an excitation source, the technique is named particle-induced X-ray emission (PIXE), The sensitivity of the PIXE method is very high for Fe and neighboring elements with a similar Z number, i.e. approximately 20 essential metallic elements." The lower detection limit for a PIXE beam is given by the ability of the X-rays to pass through the window between the chamber and the X-ray detector, which sharply decreases with the decrease of atomic number. The upper limit is dependent on the ionization cross-section, the probability of the K electron shell ionization, which decreases with the increase of atomic number. 

Neutron Activation Analysis X-Ray Fluorescence Particle-Induced X-Ray Emission Particle-Induced Nuclear Reaction Analysis Rutherford Backscattering Spectrometry Spark Source Mass Spectrometry Glow Discharge Mass Spectrometry Electron Microprobe Analysis Laser Microprobe Analysis Secondary Ion Mass Analysis Micro-PIXE... 

There are two principal sources of reliable partitioning data for any trace element glassy volcanic rocks and high temperature experiments. For the reasons outlined above, both sources rely on analytical techniques with high spatial resolution. Typically these are microbeam techniques, such as electron-microprobe (EMPA), laser ablation ICP-MS, ion-microprobe secondary ion mass spectrometry (SIMS) or proton-induced X-ray emission (PIXE). 

Ion beam probes are used in a wide range of techniques, including Secondary Ion Mass Spectroscopy (SIMS), Rutherford backscattering spectroscopy (RBS) and proton-induced X-ray emission (PIXE). The applications of these and number of other uses of ion beam probes are discussed. 

When primary X-rays are directed on to a secondary target, i.e. the sample, a proportion of the incident rays will be absorbed. The absorption process involves the ejection of inner (K or L) electrons from the atoms of the sample. Subsequently the excited atoms relax to the ground state, and in doing so many will lose their excess energy in the form of secondary X-ray photons as electrons from the higher orbitals drop into the hole in the K or L shell. Typical transitions are summarized in Figures 8.35 and 8.36. The reemission of X-rays in this way is known as X-ray fluorescence and the associated analytical method as X-ray fluorescence spectrometry. The relation between the two principal techniques of X-ray emission spectrometry is summarized in Figure 8.37. 

There are now several different types of machines that are all capable of microanalysis. All have advantages and disadvantages, but the choice of which to use is often governed by expense and availability to a particular institution. Electron probe microanalysis is by far the most popular, but here particle-induced X-ray emission (PIXE), the laser microprobe mass analyzer (LAMMA), electron energy loss spectroscopy (EELS), and secondary ion mass spectrometry (SIMS) are also considered. 

Three analytical techniques which differ in how the primary vacancies are created share the use of such X-rays to identify the elements present. In X-ray fluorescence, the solid sample is irradiated by an X-ray beam (called the primary beam), which interacts with the atoms in the solid to create inner shell vacancies, which then de-excite via the emission of secondary or fluorescent X-rays - hence the name of the technique. The second uses a beam of electrons to create the initial vacancies, giving rise to the family of techniques known collectively as electron microscopy. The third and most recently developed instrumentation uses (usually) a proton beam to cause the initial vacancies, and is known as particle- (or proton-) induced X-ray emission (PIXE). 

Another important characteristic is that ion beams can produce a variety of the secondary particles/photons such as secondary ions/atoms, electrons, positrons. X-rays, gamma rays, and so on, which enable us to use ion beams as analytical probes. Ion beam analyses are characterized by the respectively detected secondary species, such as secondary ion mass spectrometry (SIMS), sputtered neutral mass spectrometry (SNMS), electron spectroscopy, particle-induced X-ray emission (PIXE), nuclear reaction analyses (NRA), positron emission tomography (PET), and so on. 

U Cephei (V = 6.8-9.0, P = 2.493 d) is an eclipsing binary consisting of a B7V primary and a G8DI-IV secondary component. This binary is one of the semidetached Algol systems showing soft X-ray emission which is probably associated with a hot corona surrounding the secondary component (White and Marshall 1983). 

X-ray photoelectron spectroscopy (XPS), SIMS (Secondary Ion Mass Spectroscopy) and nuclear-reaction-based analyses (like RBS - Rutherford Backscattering -, and PIXE - Proton Induced X-ray Emission) have already proven their complementary potentialities. 

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