Source deuterium discharge

The usual sources of ultraviolet radiation are hydrogen or deuterium discharge lamps (the latter usually being preferred) or the mercury vapour lamp. All ultraviolet sources must be fitted with quartz or silica glass windows and none of the lamps named emits any significant amounts of radiation above 400 nm. 

There are two commonly used sources of light in UV-visible absorption spectrophotometry, hydrogen or deuterium discharge lamps and incandescent filament... 

For the ultraviolet region, a low-pressure hydrogen or deuterium discharge tube is generally used as the source. Each of these can be used from 185 to about 375 nm, but the deuterium source has about three times the spectral output of the hydrogen source. Ultraviolet sources must have a quartz window, because glass is not transparent to ultraviolet radiation. They are frequently water-cooled to dissipate the heat generated. 

The light source is commonly a tungsten filament lamp (covering the visible region of the spectrum, typically 340-8(X) nm) or a deuterium discharge lamp for the UV region (200-350 nm). For some applications, more intense sources such as a xenon or xenon/mercury arc lamp, or even lasers, may be required. 

The photodiode array detector (PDAD) measures absorption of light waves by a sample. This is considered the most powerful of the ultraviolet spectrophotometric detectors. The optical system focuses light from a deuterium source through the sample flow cell onto several photodiodes. These act as capacitators by holding a fixed amount of charge. When light strikes the photodiodes, they discharge a certain amount of current. 

Sources of ultraviolet radiation include (a) tungsten-filament incandescent lamps (b) tungsten-iodine cycle lamps with quartz envelopes (c) mercury-vapor lamps and (d) the zinc discharge lamp. Odier types are available, but enjoy only limited application. The hydrogen or deuterium lamps are used in the laboratory, but are delicate and costly for process uses. 

A light source—a tungsten filament hydrogen, mercury, or deuterium lamps a xenon discharge lamp—that provides an intense, stable, and constant radiation. 

If a continuum source is needed for absorption spectroscopy, this can be provided by discharge lamps fdled to higher densities, such that pressures can exceed 100 bar at operational temperatures. The result is a broad continuum emission with superimposed line spectra, as shown for several lamps in Fig. 14. In commercial spectrometers the deuterium lamp is commonly used for the UV region below 350 nm while the tungsten-halogen lamp is convenient for the 350 to 900 nm range. The latter is an example of a thermal source whose radiant excitance per unit wavelength closely approximates that predicted by the Planck formula for a blackbody radiator " ... 

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