Description
Every gas gives off a characteristic light when placed across a high electrical field. Spectrum tubes are built to contain different gaseous atoms or molecules. When a tube is placed into the Spectrum tube Power Supply, the 5,000V field will cause the gases to emit energy in the form of a well-defined light state.
When gas is excited by the high voltage, an electron will be excited to a higher energy level. When the electron returns to a lower energy level, it simultaneously emits a photon of light. This photon of light is always the same energy since the energy change is always the same. Therefore, each excited element emits characteristic wavelengths determined by energy level differences (∆E) present in that element.
When the spectrum tube is turned on, it may appear to be a particular color with the unaided eye. However, analysis of the spectrum with a spectrometer will reveal a series of sharp (monochromatic) emission lines. Spectrum tubes use research-grades gases and vapors to provide bright-line spectral lines of high clarity. They are designed for optimum intensity and line resolution when examined in a student-grade spectrometer equipped with a 200 line/mm (5,000 line/inch) diffraction grating.
The pressure of the various gases in spectrum tubes is a carefully controlled value that will produce the maximum quality of brightness and clarity of the spectral lines. The tube life is extended if the operation is cyclic and the tubes are never on for more than 30 seconds. Some tubes using neon, helium and other gases found in cold cathodes display signs that can run continuously with less deterioration of the quality of the spectral lines. Others, such as hydrogen, halogens, and water vapor, require more care in operating to increase the life of the spectrum tube. Pure nickel electrodes and the best research-grade gases are used, and meticulous care is taken in processing to increase service life. However, the tubes all start to contaminate at a very slow rate when used. How soon this can be detected by the user depends on the sensitivity of the measuring equipment. If the tubes are used as recommended and not allowed to get overheated, the useful life, or time it takes to detect contamination with the usual measuring equipment, is very long.
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