..... Click the link for more information. by means of tiny visible flashes produced by the radiation when it strikes a sensitive substance known as a phosphor (see phosphorescence phosphorescence (fŏs'fərĕs`əns)
..... Click the link for more information. ). Phosphors used in scintillation counters include zinc sulfide, sodium iodide, various liquids, and organic phosphors. The individual flashes are caused by absorption and reemission of radiation by the phosphor. They may be amplified by photomultiplier devices or amplified and converted to an electrical signal by photoemissive substances (see photoelectric effect photoelectric effect, emission of electrons by substances, especially metals, when light falls on their surfaces. The effect was discovered by H. R. Hertz in 1887.
..... Click the link for more information. ). Scintillation counters may be used to detect the various types of radioactivity radioactivity, spontaneous disintegration or decay of the nucleus of an atom by emission of particles, usually accompanied by electromagnetic radiation . The energy produced by radioactivity has important military and industrial applications.
..... Click the link for more information. (alpha, beta, and gamma rays), cosmic rays, and various elementary particles elementary particles, the most basic physical constituents of the universe.
Basic Constituents of Matter
Molecules are built up from the atom , which is the basic unit of any chemical element .
..... Click the link for more information. .
scintillation counter [‚sint·əl′ā·shən ‚kau̇nt·ər]
Scintillation counter
A particle or radiation detector which operates through emission of light flashes that are detected by a photosensitive device, usually a photomultiplier or a silicon PIN diode. The scintillation counter not only can detect the presence of a particle, gamma ray, or x-ray, but can measure the energy, or the energy loss, of the particle or radiation in the scintillating medium. The sensitive medium may be solid, liquid, or gaseous, but is usually one of the first two. The scintillation counter is one of the most versatile particle detectors, and is widely used in industry, scientific research, medical diagnosis, and radiation monitoring, as well as in exploration for petroleum and radioactive minerals that emit gamma rays. Many low-level radioactivity measurements are made with scintillation counters. See Particle detector
Scintillation counters are made of transparent crystalline materials, liquids, plastics, or glasses. In order to be an efficient detector, the bulk scintillating medium must be transparent to its own luminescent radiation, and since some detectors are quite extensive, covering meters in length, the transparency must be of a high order. One face of the scintillator is placed in optical contact with the photosensitive surface of the photomultiplier or PIN diode (see illustration). In order to direct as much as possible of the light flash to the photosensitive surface, reflecting material is placed between the scintillator and the inside surface of the container.
)
In many cases it is necessary to collect the light from a large area and transmit it to the small surface of a photomultiplier. In this case, a “light pipe” leads the light signal from the scintillator surface to the photomultiplier with only small loss. The best light guides and light fibers are made of glass, plastic, or quartz. It is also possible to use lenses and mirrors in conjunction with scintillators and photomultipliers. See Optical fibers
A charged particle, moving through the scintillator, loses energy and leaves a trail of ions and excited atoms and molecules. Rapid interatomic or intermolecular transfer of electronic excitation energy follows, leading eventually to a burst of luminescence characteristic of the scintillator material. When a particle stops in the scintillator, the integral of the resulting light output, called the scintillation response, provides a measure of the particle energy, and can be calibrated by reference to particle sources of known energy. Photomultipliers or PIN diodes may be operated so as to generate an output pulse of amplitude proportional to the scintillation response.
When a particle passes completely through a scintillator, the energy loss of the particle is measured. When a gamma ray converts to charged particles in a scintillator, its energy may also be determined. When the scintillator is made of dense material and of very large dimensions, the entire energy of a very energetic particle or gamma ray may be contained within the scintillator, and again the original energy may be measured. Such is the case for energetic electrons, positrons, or gamma rays which produce electromagnetic showers in the scintillator. Energy spectra can be determined in these various cases by using electronic equipment to convert amplitudes of the output pulses from the photomultiplier or PIN diode to digital form, for further processing by computers or pulse-height analyzers.
How to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit webmaster's page for free fun content.
| ?Page tools | ||
|---|---|---|
|