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.

• Crystallographic Analysis

  • The field has greatly advanced with the development of x-ray diffraction methods, where the matter analyzed is usually in its crystal form.
  • Nuclear magnetic resonance spectroscopy and x-ray crystallography have become the methods of choice for understanding three-dimensional protein structures.
  • X-ray crystallography is the primary method for determining the molecular conformation of biological macromolecules, particularly proteins and nucleic acids such as DNA and RNA.
  • Neutron crystallography is often used to help refine structures obtained by x-ray methods or to solve a specific bond; the methods are often viewed as complementary, as x-rays are sensitive to electron positions and scatter most strongly off heavy atoms, while neutrons are sensitive to nucleus positions and scatter strongly off many light isotopes, including hydrogen and deuterium.
  • Distinguish between the three methods of crystallography: X-ray, neturon and electron crystallography

• 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.

• Basic Techniques in Protein Analysis

  • The basic techniques used to analyze proteins are mass spectrometry, x-ray crystallography, NMR, and protein microarrays.
  • Crystallographers aim high-powered X-rays at a tiny crystal containing trillions of identical molecules.
  • The crystal scatters the X-rays onto an electronic detector that is the same type used to capture images in a digital camera.
  • After each blast of X-rays, lasting from a few seconds to several hours, the researchers precisely rotate the crystal by entering its desired orientation into the computer that controls the X-ray apparatus.
  • This enables the scientists to capture in three dimensions how the crystal scatters, or diffracts, X-rays.

• 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.

• Determining Atomic Structures by X-Ray Crystallography

  • X-ray crystallography is a method of determining the arrangement of atoms within molecules.
  • X-ray crystallography is a method for determining the arrangement of atoms within a crystal structure.
  • The crystal is typically rotated with respect to different axes and shot again with X-rays, so that diffraction patterns from all angles of the X-rays hitting the crystal are recorded.
  • When bombarded with x-ray radiation, crystals exhibit a characteristic diffraction pattern.
  • An X-ray diffraction pattern of a crystallized protein molecule.

• 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 Analysis

  • X-ray diffraction is caused by constructive interference of x-ray waves that reflect off internal crystal planes.
  • A thin film or layer of powder is fixed in the path of monochromatic x-rays.
  • A detector measures x-rays from the sample over a range of angles.
  • The output graph displays x-ray intensity over 2 theta, the angle of the detector.
  • X-ray diffraction analysis workflow.

• 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.