| beam splitter | <radiobiology> Optical device for dividing a beam of electromagnetic radiation into two or more separate beams. (09 Oct 1997) |
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| beam tree | <botany> A tree (Pyrus aria) related to the apple. Origin: AS. Beam a tree. See: Beam. Source: Websters Dictionary (01 Mar 1998) |
| beam-wall reaction | <radiobiology> Fusion reaction which occurs from the collision of a fast beam ion with an ion embedded in or adsorbed onto the reactor wall. (09 Oct 1997) |
| cantilever beam | In dentistry, a beam that is supported by only one fixed support at only one of its ends. (05 Mar 2000) |
| radium beam therapy | Therapeutic use of radium rays, the source of which is a quantity of radium at a distance from the patient. Synonym: radium beam therapy. (05 Mar 2000) |
| restrained beam | In dentistry, a beam that has two or more supports, at least one of which permits some freedom of rotation to the point of support but not as much as if the support were a free support. (05 Mar 2000) |
| continuous beam | In dentistry, a beam that continues over three or more supports, those supports not at the beam ends being equally free supports. (05 Mar 2000) |
| horizontal beam film | A radiograph made with the central axis of the X-ray beam parallel to the floor, able to show an air-fluid level. (05 Mar 2000) |
| simple beam | In dentistry, a straight beam that has only two supports, one at either end. (05 Mar 2000) |
| neutral axis of straight beam | The axis perpendicular to the plane of loading of a beam at stresses within the proportional limit; it lies at the gravity axis of the cross-section of the beam. (05 Mar 2000) |
| neutral beam injection | <radiobiology> This is one of the fundamental plasma heating methods. A particle accelerator is used to create fast ion beams (the particle energies are on the order of 100 keV), the ion beam is then passed through a neutral gas region, where the ions neutralise via charge-exchange reactions with the neutral gas. The neutralised beam is then injected into a magnetically confined plasma. The neutral atoms are unaffected (not confined) by the magnetic field, but ionize as they penetrate into the plasma. The high-energy ions then transfer some of their energy to the plasma particles in repeated collisions, and heat the plasma. (09 Oct 1997) |
| aperture for electron microscopy | <technique> Anode aperture: The opening in the accelerating voltage anode shield of the electron gun through which the electrons must pass to irradiate the specimen. Condenser aperture: An opening in the condenser lens controlling the number of electrons entering the lens and the angular aperture of the electron beam. The angular aperture can also be controlled by the condenser lens current. Physical objective aperture: A metallic diaphragm, with a small central hole, used to limit the cone of electrons accepted by the objective lens. This improves image-contrast since highly scattered electrons are prevented from arriving at the Gaussian image plane and therefore cannot contribute to background fog. Aplanatic. Free from spherical aberration and coma. (05 Aug 1998) |
| Auger electron | An electron ejected from a lower energy orbital after a photoelectric interaction of an X-ray photon with a K-shell electron by the characteristic radiation photon; the Auger electron recoils with energy equal to the characteristic radiation less the difference in shell binding energies. See: photoelectric effect. (05 Mar 2000) |
| backscattered electron | <microscopy> Produced by an incident electron colliding with the nucleus of an atom in the specimen. The incident electron is then scattered backward about 180 degrees with no appreciable loss of energy, an elastic collision. (05 Aug 1998) |
| backscattered electron imaging | <microscopy> The production of backscattered electrons from a sample varies directly with the specimen's average atomic number, higher atomic number elements produce more backscattered electrons than lower atomic number ones. Detection of Backscattered Electrons is achieved by using a donut shaped solid state saemiconductor device mounted on the bottom of the objective lens. When Backscattered Electrons strike the detector electron-hole pairs are created which are then counted. This quantity is translated into a pixel intensity and displayed on the CRT, forming the image. By splitting the detector into halves (or quadrants) differences in the signal level on the individual detector segments provide surface topography information. (05 Aug 1998) |