File Name: continuous and characteristic x ray spectrum .zip
Each type of atom or element has its own characteristic electromagnetic spectrum. In this section, we explore characteristic x rays and some of their important applications. We have previously discussed x rays as a part of the electromagnetic spectrum in Photon Energies and the Electromagnetic Spectrum.
X-rays , also known as X-radiation , refers to electromagnetic radiation no rest mass, no charge of high energies.
X-ray spectra - continuous and characteristic X-ray spectra. The spectrum from an X-ray tube contains two distinct parts :. It consists of radiations of all possible wavelengths, from a certain lower limit to higher values continuously, as in the case of visible light.
The Continuous X-Ray Spectrum
Characteristic X-rays are emitted when outer- shell electrons fill a vacancy in the inner shell of an atom , releasing X-rays in a pattern that is "characteristic" to each element. Characteristic X-rays were discovered by Charles Glover Barkla in ,  who later won the Nobel Prize in Physics for his discovery in Characteristic X-rays are produced when an element is bombarded with high-energy particles, which can be photons, electrons or ions such as protons.
When the incident particle strikes a bound electron the target electron in an atom, the target electron is ejected from the inner shell of the atom. After the electron has been ejected, the atom is left with a vacant energy level , also known as a core hole. Outer-shell electrons then fall into the inner shell, emitting quantized photons with an energy level equivalent to the energy difference between the higher and lower states.
Each element has a unique set of energy levels, and thus the transition from higher to lower energy levels produces X-rays with frequencies that are characteristic to each element. The different electron states which exist in an atom are usually described by atomic orbital notation, as is used in chemistry and general physics.
However, X-ray science has special terminology to describe the transition of electrons from upper to lower energy levels: traditional Siegbahn notation , or alternatively, simplified X-ray notation. Similarly, when an electron falls from the M shell to the K shell, the X-ray emitted is called a K-beta X-ray.
Sometimes, however, instead of releasing the energy in the form of an X-ray, the energy can be transferred to another electron, which is then ejected from the atom. This is called the Auger effect. Characteristic X-rays can be used to identify the particular element from which they are emitted. This property is used in various techniques, including X-ray fluorescence spectroscopy , particle-induced X-ray emission , energy-dispersive X-ray spectroscopy , and wavelength-dispersive X-ray spectroscopy.
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Characteristic x-rays are emitted from heavy elements when their electrons make transitions between the lower atomic energy levels. The continuous distribution of x-rays which forms the base for the two sharp peaks at left is called "bremsstrahlung" radiation. X-ray production typically involves bombarding a metal target in an x-ray tube with high speed electrons which have been accelerated by tens to hundreds of kilovolts of potential. The bombarding electrons can eject electrons from the inner shells of the atoms of the metal target. Those vacancies will be quickly filled by electrons dropping down from higher levels, emitting x-rays with sharply defined frequencies associated with the difference between the atomic energy levels of the target atoms. The frequencies of the characteristic x-rays can be predicted from the Bohr model. Moseley measured the frequencies of the characteristic x-rays from a large fraction of the elements of the periodic table and produced a plot of them which is now called a " Moseley plot ".
The cut-off wavelength of the continuous X-ray spectrum is related to the accelerating The characteristic X-rays are emitted when an electron. (in atom) makes a  Properties of X-rays (pdf), Stanford.  Features of X-rays.
It has long been known that the x-rays emitted from an x-ray tube contain radiation characteristic of the material of the x-ray target superimposed upon a continuous spectrum. As early as Winkelmann and Straubel had noticed a scattered radiation which was characteristic of fluor spar; and later the characteristic x-rays scattered by different elements were studied systematically in a series of classic researches by Barkla. However, the actual separation of different wave-lengths into a spectrum was not possible until Friedrich , Knipping and Laue showed that crystals act as three dimensional diffraction gratings.
Under the assumption that the target of an x-ray tube is a plane mirror which completely reflects the electron waves, the characteristics of the continuous x-ray spectrum are deduced from the principles of wave-mechanics. It is also assumed that the velocity of the electrons is so small that its square may be neglected in comparison to c 2. The radiation due to a single transition is practically unidirectional, the direction of the beam Nadelstrahl being determined by the conservation laws of energy and momentum. This result is due to the simplified model, and not to general principles. The plane of the target is one of mirror symmetry for the intensity distribution—a result which is again inseparable from the model.
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