Mercury vapor arc lamps

For irradiation at 254 nm a low pressure mercury vapor arc lamp is used. The 185 nm light emitted by these lamps is absorbed by the lamp envelope and the vessel containing the sample. Ninety percent of the remaining light is at 254 nm and, if desired, the other weak spectral lines in the UV and visible can be removed with the appropriate filter (see below). As the pressure of vapor inside a mercury lamp is increased the 254 nm line becomes weaker relative to other spectral lines because of self-absorption. Useful emission in the 300 to 400 nm range is obtained from medium... 

Hazardous Decomp. Prods. Heated to decomp., emits toxic fumes of Hg HMIS Health 3, Flammability 0, Reactivity 1 Uses Amalgam dental fillings catalyst electrical apparatus cathodes for prod, of chlorine and caustic soda instrument indicator fluid thermometers barometers mercury vapor arc lamps extraction metallurgy mirror coating boilers coolant and neutron absorber in nuclear power plants vacuum pumps... 

Exposure systems for most resists use ultraviolet (UV) light from mercury vapor arc lamps. The resists are designed to react either to abroad spectrum of UV wavelengths, or they are formulated to react preferentially to one or more ofthe main spectrum lines emitted from the lamp (e g., g-line at 435 mn, h-line at 405 nm, and i-line at 365 nm). 

Ultraviolet light sources are based on the mercury vapor arc. The mercury is enclosed ia a quart2 tube and a potential is appHed to electrodes at either end of the tube. The electrodes can be of iron, tungsten, or other metals and the pressure ia a mercury vapor lamp may range from less than 0.1 to >1 MPa (<1 to >10 atm). As the mercury pressure and lamp operating temperatures are iacreased, the radiation becomes more iatense and the width of the emission lines iacreases (17). 

Additive lamps Arc or microwave medium-pressure mercury vapor UV lamps that have small amounts of different metal halides added to the mercury in the lamp. The halides emit their characteristic wavelengths in addition to mercury additions (this term is preferred over doped lamps). 

Figure 13. Line and continuous spectra from various light sources ----= Xenon lamp -------= Mercury vapor arcs .= Hydrogen lamp...

Lighting. An important appHcation of clear fused quartz is as envelop material for mercury vapor lamps (228). In addition to resistance to deformation at operating temperatures and pressures, fused quartz offers ultraviolet transmission to permit color correction. Color is corrected by coating the iaside of the outer envelope of the mercury vapor lamp with phosphor (see Luminescent materials). Ultraviolet light from the arc passes through the fused quartz envelope and excites the phosphor, produciag a color nearer the red end of the spectmm (229). A more recent improvement is the iacorporation of metal haHdes ia the lamp (230,231). 

Interest in the photochemistry of boron compounds dates back as far as 1913 when Alfred Stock investigated the effects of light from a mercury vapor lamp on diboran 6) and on tetraboran 10). In the case of diborane(6) he commented UV light will also decompose B2H6. The volume of a sample in a quartz tube increased by 1/6 after 24 hours exposure to a mercury-arc lamp, and a pale yellow crystalline substance appeared. Stock also observed that B4H q decomposition to B2H is not noticeably influenced by sunlight. 

A diagram of the author s original spectrofluorimeter is shown in Figure 3. The light source, S, was either a 1 kw. compact source mercury vapor lamp, or for the measurement of fluorescence excitation spectra, a 375 w. xenon arc. The required frequency of exciting light was isolated by means of a Hilger 1)247 quartz prism monochromator, Mj, and... 

Mercury arcs are employed in these lamps because of the spectral distribution they emit, and because mercury vapor is relatively inert. It does not attack either the glass or the electrode materials (Kirk 1982). This contributes to the long lifetimes of mercury lamps. Low pressure mercury lamps are commonly called fluorescent lamps. High pressure mercury lamps are used in industrial environments and for street lighting and floodlighting. Other applications for mercury vapor lamps include motion-picture projection, photography, and heat therapy. 

The lamp is mounted securely at its ends and connected to a source of direct current preferably 220 volts or 500 volts through suitable resistances and a switch. The switch is closed and a small Bunsen flame is played on the capillary between A and B. The mercury vaporizes and the arc strikes and is localized between the two bulbs. As soon as the lamp starts, water is turned on so that it flows down around the lamp in a large stream. The cold water keeps the cement intact and preserves the lamp. The energy is so intense that without water-cooling the quartz would be melted immediately. Hard water may be used provided that it passes over the lamp so rapidly that there is not time to heat up the water and deposit lime. The mounting of the lamp may be varied for different purposes. The lamp may be placed in front of a quartz window in a copper tank which is partially drained until the lamp is started. After starting, the tank is allowed to fill to an outlet near the top thus covering the lamp. 

Low-pressure mercury lamp [Arc) A type of resonance lamp which contains mercury vapor at pressures of about 0.1 Pa (0.75 x lO Torr 1 Torr = 133.3 Pa). At 25 °C, such a lamp emits mainly at 253.7 and 184.9 run. Other terms used for such a lamp are germicidal, cold and hot cathode. Wood lamp. 

Medium-pressure mercury lamp (Arc) Radiation source containing mercury vapor at pressures ranging from 100 to several hundred kPa (1 atm = 101.325 kPa). Emits mostly from 310 to 1000 nm with most intense Hnes at 300, 303, 313, 334, 366, 405, 436, 546, and 578 nm. 

Mercury-xenon lamp (Arc) An intense source of ultraviolet, visible, and near infrared radiation produced by an electrical discharge in a mixture of mercury vapor and xenon under high pressure. 

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