Discharge lamp

Ultraviolet photoelectron spectroscopy (UPS) is a variety of photoelectron spectroscopy that is aimed at measuring the valence band, as described in sectionBl.25.2.3. Valence band spectroscopy is best perfonned with photon energies in the range of 20-50 eV. A He discharge lamp, which can produce 21.2 or 40.8 eV photons, is commonly used as the excitation source m the laboratory, or UPS can be perfonned with synchrotron radiation. Note that UPS is sometimes just referred to as photoelectron spectroscopy (PES), or simply valence band photoemission. 

Until the advent of lasers the most intense monochromatic sources available were atomic emission sources from which an intense, discrete line in the visible or near-ultraviolet region was isolated by optical filtering if necessary. The most often used source of this kind was the mercury discharge lamp operating at the vapour pressure of mercury. Three of the most intense lines are at 253.7 nm (near-ultraviolet), 404.7 nm and 435.7 nm (both in the visible region). Although the line width is typically small the narrowest has a width of about 0.2 cm, which places a limit on the resolution which can be achieved. 

Whereas the emission spectrum of the hydrogen atom shows only one series, the Balmer series (see Figure 1.1), in the visible region the alkali metals show at least three. The spectra can be excited in a discharge lamp containing a sample of the appropriate metal. One series was called the principal series because it could also be observed in absorption through a column of the vapour. The other two were called sharp and diffuse because of their general appearance. A part of a fourth series, called the fundamental series, can sometimes be observed. 

It is possible to change the conditions in the helium discharge lamp so that the helium is ionized predominantly to He (He II). The radiation is due mainly to the n = 2 — n = transition of He II (analogous to the first member of the Lyman series of the hydrogen atom in Figure 1.1) at 30.4 nm with an energy of 40.81 cY A thin aluminium foil filter can be used to remove any He I radiation. 

When neon is used in a discharge lamp radiation is produced predominantly with two close wavelengths, 74.4 nm and 73.6 nm, corresponding to energies of 16.67 eV and 16.85 eV, making this source rather less useful than the more tmly monochromatic, and more highly energetic. He I source. 

GLimm-lainpe,/. glow (discharge) lamp. -Hcht,... 

Luminaire types (a) parabolic aluminized reflector (PAR) lamp holder (b) incandescent, compact fluorescent or high-intensity discharge lamp downlight (c) lensed fluorescent lamp luminaire (d) wall-mounted compact fluorescent lamp luminaire (e) wall-mounted high-intensity discharge lamp luminaire (f) roadway luminaire (g) low bay industrial luminaire (h) multi-faceted reflector (MR) lamp (i) pendant sphere. 

Fluorescent lamps are termed a low-pressure discharge lamp. An electric current passes through mer-... 

Electrical units 503, 519 Electrification due to wiping 77 Electro-analysis see Electrolysis and Electrogravimetry Electrochemical series 63 Electro-deposition completeness of, 507 Electrode potentials 60 change of during titration, 360 Nernst equation of, 60 reversible, 63 standard 60, (T) 62 Electrode reactions 505 Electrodeless discharge lamps 790 Electrodes antimony, 555 auxiliary, 538, 545 bimetallic, 575... 

The top and the bottom x-ray detector each contain a multiplier phototube coated with phosphor. This tube compares the intensity of the x-ray beam entering the detector with that of the light from the reference standard, a discharge lamp. The reference beam is part of a circuit that maintains the x-ray source at constant intensity. The deviation wedge comes to rest when the intensities of the transmitted x-ray beams stand in a predetermined ratio. At this point, the unbalance in the servo system has been compensated, and the position of the deviation wedge consequently indicates the thickness of the strip. In 1955, this application was made fully automatic that is, the unbalance (or error signal) just mentioned was used to readjust tandem cold reduction mills of the United States Steel Corporation. Automatic control proved significantly more effective than manual control. 

A discharge lamp rated with a power of 25 W (1 W = 1 J s-1) emits yellow light of wavelength 580 nm. How many photons of yellow light does the lamp generate in 1.0 s ... 

Self-Test 1.5A Another discharge lamp produces 5.0 J of energy per second in the blue region of the spectrum. How many photons of blue (470 nm) light would the lamp generate if it were left on for 8.5 s ... 

This type, made by the General Electric Co., is resistant to sodium vapour and is used in sodiiun vapour discharge lamps. It has a very high boric oxide content, a low softening temperature, and a low electrical resistance. It is used as an internal layer in soda glass tubing X.8. ... 

High voltage hydrogen discharge lamps which give continuous radiation in the ultra-violet can be constructed quite simply and elaborate designs are unnecessary for many purposes. A very simple... 

W. West (1949) gives a survey of soiue discharge lamps of different types in which he provides details of the operating conditions for such lamps. 

Air or water cooled mercury discharge lamps find many uses, one of the more obvious of which is the study of photochemical reactions. These lamps are usually made of vitreous silica because of its low thermal expansion, high melting point and its transparency to ultraviolet radiation. Their operating pressure has a profound effect on the spectral distribution of the radiation produced and therefore it is important to consider the requirements in the design of such lamps. 

A typical photoionization detector is shown in Figure 3.11. The UV source is a discharge lamp, containing an inert gas or gaal mixture at low pressure, that emits monochromatic light of 1... 

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