X-ray spectroscopy

Examples of X-ray spectroscopy in the following topics:

• X-Rays

  • It is also used for material characterization using X-ray spectroscopy .
  • X-rays with photon energies above 5 to 10 keV (below 0.2-0.1 nm wavelength), are called hard X-rays, while those with lower energy are called soft X-rays.
  • Since the wavelength of hard X-rays are similar to the size of atoms, they are also useful for determining crystal structures by X-ray crystallography.
  • By contrast, soft X-rays are easily absorbed in air and the attenuation length of 600 eV (~2 nm) X-rays in water is less than 1 micrometer.
  • The distinction between X-rays and gamma rays is somewhat arbitrary.

• X-Ray Spectra: Origins, Diffraction by Crystals, and Importance

  • In a previous Atom on X-rays, we have seen that there are two processes by which x-rays are produced in the anode of an x-ray tube.
  • In one process, the deceleration of electrons produces x-rays, and these x-rays are called Bremsstrahlung, or braking radiation.
  • The x-ray spectrum in is typical of what is produced by an x-ray tube, showing a broad curve of Bremsstrahlung radiation with characteristic x-ray peaks on it.
  • The process is called x-ray diffraction because it involves the diffraction and interference of x-rays to produce patterns that can be analyzed for information about the structures that scattered the x-rays.
  • These can be studied using x-ray crystallography.

• X-Rays

  • X-radiation (composed of x-rays) is a form of electromagnetic radiation.
  • X-rays can be generated by an x-ray tube, a vacuum tube that uses high voltage to accelerate the electrons released by a hot cathode to a high velocity.
  • These x-rays have a continuous spectrum.
  • The intensity of the x-rays increases linearly with decreasing frequency, from zero at the energy of the incident electrons, the voltage on the x-ray tube.
  • Its unique features are x-ray outputs many orders of magnitude greater than those of x-ray tubes, wide x-ray spectra, excellent collimation, and linear polarization.

• X-Ray Imaging and CT Scans

  • Radiography uses x-rays to view material that cannot be seen by the human eye by identifying areas of different density and composition.
  • X-ray imaging, or radiography, used x-rays to view material within the body that cannot be seen by the human eye by identifying areas of different density and composition.
  • X-ray radiographs are produced by projecting a beam of X-rays toward an object, in medical cases, a part of the human body.
  • Depending on the physical properties of the object (density and composition), some of the X-rays can be partially absorbed.
  • CT scans, or computed tomography scans use a combination of X-ray radiography and tomography to produce slices of areas of the human body.

• Gamma Rays

  • Gamma rays have characteristics identical to X-rays of the same frequency—they differ only in source.
  • They have many of the same uses as X-rays, including cancer therapy.
  • The distinction between X-rays and gamma rays has changed in recent decades.
  • Originally, the electromagnetic radiation emitted by X-ray tubes almost invariably had a longer wavelength than the radiation (gamma rays) emitted by radioactive nuclei.
  • Thus, gamma rays are now usually distinguished by their origin: X-rays are emitted by definition by electrons outside the nucleus, while gamma rays are emitted by the nucleus.

• X-Ray Diffraction

  • The principle of diffraction is applied to record interference on a subatomic level in the study of x-ray crystallography.
  • X-ray diffraction was discovered by Max von Laue, who won the Nobel Prize in physics in 1914 for his mathematical evaluation of observed x-ray diffraction patterns.
  • In x-ray crystallography, the term for diffraction is Bragg diffraction, which is the scattering of waves from a crystalline structure.
  • Similarly, the x-ray beam that is diffracted off a crystal will have some parts that have stronger energy, and others that lose energy.
  • The XRD machine uses copper metal as the element for the x-ray source.

• X-Rays and the Compton Effect

  • Compton explained the X-ray frequency shift during the X-ray/electron scattering by attributing particle-like momentum to "photons".
  • By the early 20th century, research into the interaction of X-rays with matter was well underway.
  • It was observed that when X-rays of a known wavelength interact with atoms, the X-rays are scattered through an angle $\theta$ and emerge at a different wavelength related to $\theta$.
  • In his paper, Compton derived the mathematical relationship between the shift in wavelength and the scattering angle of the X-rays by assuming that each scattered X-ray photon interacted with only one electron.
  • Therefore, you can say that Compton effects (with electrons) occur with x-ray photons.

• Diffraction Revisited

  • X-ray diffraction is a commonly used tool in materials research.
  • In comparison, X-rays interact with the spatial distribution of the valence electrons, while neutrons are scattered by the atomic nuclei through the strong nuclear force.
  • They are scattered by the nuclei of the atoms, unlike X-rays, which are scattered by the electrons of the atoms. 
  • Thus, neutron diffraction has some key differences compared to more common methods using X-rays or electrons.
  • Compare application of X-ray, electron, and neutron diffraction for materials research

• Diffraction Gratings: X-Ray, Grating, Reflection

  • X-ray crystallography is a method of determining the atomic and molecular structure of a crystal, in which the crystalline atoms cause a beam of X-rays to diffract into many specific directions.
  • In an X-ray diffraction measurement, a crystal is mounted on a goniometer and gradually rotated while being bombarded with X-rays, producing a diffraction pattern of regularly spaced spots known as reflections (see ).
  • Each dot, called a reflection, in this diffraction pattern forms from the constructive interference of scattered X-rays passing through a crystal.

• Further Reading

  • To learn more about faint x-ray structure in the Crab nebula, consult
  • ~H. & Fesen, R.A. 2006, "Faint X-Ray Structure in the Crab Pulsar Wind Nebula,'' ApJ, 652, 1277