![]() This is often termed as working “at the line focus” or “at the square focus,” respectively. In this case the projection of the focus into the plane perpendicular to this X-ray path is a line with dimensions 10 × 0.1 mm on the “long” side of the focus in its “narrow” side, the focus appears as a radiating square of dimensions 1 × 1 mm. Frequently the size of the focus is 10 × 1 mm and the X-ray path has the usual 6° inclination from the horizontal plane of the focus. In the following discussion the case of a vertically mounted X-ray tube is assumed, as this appears to be preferred by most workers.Īnother basic decision concerns the type of window to be used for the camera. Better mechanical stability and access to all four windows favor the vertical position, but several types of small-angle cameras (e.g., the Rigaku Denki goniometer) require a horizontal tube. First, one has to decide whether the tube should be mounted vertically or horizontally. Laggner, in Encyclopedia of Physical Science and Technology (Third Edition), 2003 VI.A.2 Installation of X-Ray Tube and Cameraįor this description it is assumed that an X-ray tube with line focus and four windows is used. Thus the spectrum emitted from the anode consists of the continuous bremsstrahlung and the characteristic X-ray lines of the anode material. (2) An inner-shell electron of an atom is ejected if the kinetic energy exceeds the binding energy, and from this the characteristic X-rays of the anode material are emitted. (1) An electron enters the electric field of an atomic orbital and is slowed down, and the loss of kinetic energy during slowing down is emitted as electromagnetic radiation, called bremsstrahlung. Two effects can occur if the accelerated electrons interact with the atoms of the anode material. The electrons are emitted from a heated tungsten filament which serves as the cathode and are accelerated by a high voltage applied between the filament and a metal anode. The X-ray tubes are built as a vacuum-sealed metal glass cylinder. In X-ray tubes, the X-rays are produced by the bombardment of matter with accelerated electrons. Utz Kramar, in Encyclopedia of Spectroscopy and Spectrometry (Second Edition), 1999 X-Ray Tubes 24 Beam fluxes greater than those obtained with modern rotating anodes have already been reported, with the theoretical capability of increasing this flux by another three orders of magnitude. ![]() Microfocus X-ray tubes are usually not as intense a source as modern rotating anodes, although the focused electron beam allows a larger take-off angle the biggest advantage is that they are much easier to maintain.Ī new method of generating X rays that is not yet commercially available uses an electron-impact beam impinging on a stream of liquid gallium. Another option to increase the intensity is to focus the electron beam on a very small area of the anode ( microfocus X-ray tubes). These sources are called rotating anodes. ![]() More intense beams can be obtained if the anode is rotated at speeds of 6000 rpm or more, as the intensity of the output radiation is not limited by the cooling rate of the metal target. This limits the power at which they can be operated, and therefore the intensity of the beam achieved. If the take-off angle is larger, the beam will be more intense, but the quality of the focus will degrade.Ī problem with X-ray tubes is that the electrons produce a large amount of heat when they strike the anode. Another important parameter is the take-off angle at which the X-rays emerging from the anode are selected. X-ray tubes typically use filters to absorb K β radiation and the smaller white beam component. Copper, with the K α emission line at 1.54 Å is usually the preferred target, although recently chromium sources have been suggested for de novo structure solution using the anomalous signal from sulfur, calcium and other intrinsic medium-weight atoms in the crystal 23 the longer emission wavelength of chromium (2.29 Å) results in a high value of the anomalous scattering factor component f″ arising from those atoms. The resulting rapid deceleration of the electrons causes the emission of white radiation ( Bremsstrahlung) as well as discrete, much more intense radiation at the characteristic wavelength of emission of the target metal. The X-ray tubes produce X-rays when an energetic beam of electrons hits a metallic target (anode). González, in Comprehensive Biophysics, 2012 1.5.2.1.1 X-ray tubes and rotating anodes
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |