Radiation reflector

A more elaborate example of induct on heating is shown in Fig. 5.8, which showsareactordesignedforthedeposition of silicon epitaxy in semiconductor devices (see Ch. 13).Thepowerissuppliedby a solid-state high-frequency (20 KHz) generator. A radiation reflector, shown in Detail A, increases the efficiency and uniformity of deposition. Pressure varies from 100 mbar to 1 atm. 

The albedo of earth surface varies from about 0.1 for the oceans to 0.6-0.9 for ice and clouds which mean the clouds, snow and ice are good radiation reflectors while liquid water is not. In fact, snow and ice have the highest albedos of any parts of the earth s surface Some parts of Antarctic reflect up to 90% of incoming solar radiation. 

Criticality Precautions. The presence of a critical mass of Pu ia a container can result ia a fission chain reaction. Lethal amounts of gamma and neutron radiation are emitted, and a large amount of heat is produced. The assembly can simmer near critical or can make repeated critical excursions. The generation of heat results eventually ia an explosion which destroys the assembly. The quantity of Pu required for a critical mass depends on several factors the form and concentration of the Pu, the geometry of the system, the presence of moderators (water, hydrogen-rich compounds such as polyethylene, cadmium, etc), the proximity of neutron reflectors, the presence of nuclear poisons, and the potential iateraction with neighboring fissile systems (188). As Httle as 509 g of Pu(N02)4 solution at a concentration Pu of 33 g/L ia a spherical container, reflected by an infinite amount of water, is a critical mass (189,190). Evaluation of criticaUty controls is available (32,190). 

For opaque materials, the reflectance p is the complement of the absorptance. The directional distribution of the reflected radiation depends on the material, its degree of roughness or grain size, and, if a metal, its state of oxidation. Polished surfaces of homogeneous materials reflect speciilarly. In contrast, the intensity of the radiation reflected from a perfectly diffuse, or Lambert, surface is independent of direction. The directional distribution of reflectance of many oxidized metals, refractoiy materials, and natural products approximates that of a perfectly diffuse reflector. A better model, adequate for many calculational purposes, is achieved by assuming that the total reflectance p is the sum of diffuse and specular components p i and p. ... 

In Western Europe the largest user is the vehicle construction industry where ABS has been used for fascia panels, door covers, door handles, radiator grilles, ventilation system components, heater housings, seat belt fastenings, console panels, loudspeaker housings, interior trim and other uses. For some years there was extensive use of electroplated ABS. Whilst this continues to be used for nameplates, reflectors and other parts where a bright reflecting surface is a requirement, it has tended to fall out of favour simply for decoration. 

One way of implementing the UV disinfection process at existing activated sludge plants involves suspending the UV lights (in the form of low-pressure mercury arc UV lamps with associated reflectors) above the secondary clarifiers. The effluent is exposed to the UV radiation as it rises over the wire in a thin film. 

Fig. 7.18. Instrumental arrangement for the measurement of total reflection x-ray fluorescence. The x-rays from the source (A) are allowed to impinge on the sample mounted on a reflector plate (B). Most of the incident radiation bounces off the sample (C), but some results in the production of XRF (D), which is measured by the detector (E).

Gold is classed as a heavy, noble metal located just below copper and silver in group 11 of the periodic table. Gold is a good conductor of electricity as well as an excellent heat reflector of infrared radiation, which makes it an efircient thin coating on glass in skyscrapers to reflect the heat of sunhght. 

Other potential applications of photonic crystals include crystals with rows of holes to guide radiation around sharp bends (something that cannot be attained with conventional optical fibres), nanoscopic lasers formed from thin films, ultrawhite pigment formed from a regular array of submicron titanium dioxide particles, radio frequency reflectors for magnetic resonance imaging (MRI) and LEDs. 

UV reflectors also reflect radiation energy in the visible and infrared (IR) energy spectral regions at least as efficiently as in the UV region. This is undesirable in such cases where the substrate or the piece being irradiated is heat sensitive. To overcome this, the surface of the reflector is coated with... 

Dichroic reflector A reflector having reduced reflectance to long wavelengths (IR radiation) also called "cold mirror."... 

Infrared Radiance is the amount of infrared energy primarily emitted by the quartz envelope of the UV source. This energy is collected and focused, with the UV energy on the surface of the substrate to the extent depending on the IR reflectivity and efficiency of the reflector. Infrared radiation can be expressed in energy or irradiance units but, most commonly, the surface temperature it generates is of primary interest. The heat it produces may be a benefit or a nuisance.2... 

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