Shielding, from radiation

A.17 Spacecraft are commonly clad with aluminum to provide shielding from radiation. Adequate shielding requires that the cladding provide 20. g of aluminum per square centimeter. How thick does the aluminum cladding need to be to provide adequate shielding ... 

Time and shielding can be merged into a single factor. The shelters described in Section 5.2.1 (walls, basements, etc.) really serve as shields from radiation, heat, fallout, and even from the air blast and flying debris. At the moment of explosion, radiation and heat travel at the speed of light and expose unshielded victims. At the instant of realization that a nuclear weapon has exploded, an individual should move as quickly as possible to a location behind a rugged shielding material. 

Both the heat and mass transfer coefficients are functions of air velocity. However, at air speeds greater than about 15 ft/s (4.5 m/s), the ratio h kgis approximately constant. The wet-bulb depression is directly proportional to the difference between the humidity at the surface and the humidity in the bulk of the air. In the wet- and dry-bulb hygrometer, the wet-bulb depression is measured by two thermometers, one of which is fitted with a fabric sleeve wetted with water. These thermometers are mounted side by side and shielded from radiation, an effect neglected in the derivation above. Air is drawn over the thermometers by means of a small fan. The derivation of the humidity from the wet-bulb depression and a psychrometric chart are discussed later. 

The shortgrass-vegetation radiation field consisted of 1.2 hectares in north-central Colorado and included a 8750-Ci Cs source that was suspended 1 m above the ground surface. The radiation field was divided into six sectors a control sector shielded from radiation, two chronically irradiated sectors, and... 

It should be noted that all bodies radiate to all others. Thus, any warm object within an infrared spectrophotometer may become a source radiating more energy than it receives from its surroundings. The optical path in an instrument is always carefully shielded from radiation from hot electronic components. Potentially troublesome, however, are warm samples which, of necessity, are directly in the optical path. For example, a sample at ITC (350°K, 17rF) exhibits a radiation peak at 8.4 whose intensity is 1.7 % of that due to a 1500°K source at the same wavelength. Because of the slower decrease with wavelength of the 350°K source compared to the 1500°K source, the former radiates about 6% as much energy as the latter at 15 fx. 

Similar experiments were performed with an unsilvered helium dewar, and with that dewar wrapped on the outside with aluminum foil. In both cases the temperature distribution was qualitatively the same as with the silvered dewar. Because of the decreased shielding from radiation, the evaporative gas flow from the helium bath was greater than before. The primary effect of this was to lower by a few degrees the vapor temperature at which the gradient increased. The distance of this point from the helium surface still corresponded to the location of the nitrogen surface. 

Different Wavelengths, 10-242 Series expansions, A-65 to 67 Shielding, from radiation, 10-235 to 239,16-46 SI units... 

The dry bulb temperature (DBT) is the temperature of air measured by a thermometer freely exposed to the air but shielded from radiation and moisture. The wet-bulb temperature (0w) is the temperature a parcel of air would have if it were cooled to saturation (100% relative humidity) by the evaporation of water into it, with the latent heat being supplied by the parcel. In other words, wet bulb temperature is the temperature reached by water surface if the air is passed over it. Wet bulb temperature is a function of dry bulb temperature and humidity. The chart shows dry bulb temperature on the x-axis and moisture content on the y-axis. Any point below the saturation line represents air that is unsaturated, therefore, the chart has relative humidity cxirves going up to 100% relative humidity. Wet bulb temperature lines are constant enthalpy or adiabatic cooling lines. The change in composition of... 

Figure 16.2. LIDO, designed to study materials for shielding from radiation in a submarine.

The sixth component of the system is the shield, which protects materials and workers from radiation, especially neutrons and gamma rays. 

Ra.dia.tlon Shielding. Like lead, bismuth absorbs radiation. Therefore, bismuth ahoys are widely used in the medical industry during radiation therapy. The ahoy is molded to the shape of various organs that are to be shielded. Then the molds are placed between the radiation source and the patient to protect the patient s vital organs from radiation exposure. 

The transfer of heat from a source to a receiver by radiant energy is radiation. The sun transfers its energy to the earth by radiation. A fire in a fireplace is another example of radiation. The fire in the fireplace heats the air in the room and by convection heats up the room. At the same time, when you stand within line of sight of the fireplace, the radiant energy coming from the flame of the fire itself makes you feel warmer than when you are shielded from the line of sight of the flame. Heat is being transferred both by convection and by radiation from the fireplace... 

The nuclear reactor also must be shielded against the emission of radioactive material to the external environment. Suitable radiation controls include both thermal and biological shielding systems. Radiation from alpha particles (a rays) and beta particles ((3 rays) has little penetrating power, but gamma rays have deep penetration properties. Neutron radiation is, however, the primary area of risk. Typically, extremely thick concrete walls are used as a neutron absorber, but lead-lined concrete and special concretes are also used. 

Neglecting any temperature drop across the shield (which has a surface emissivity esh), then in the steady state, the transfer rate of radiant heat to the shield from the surface 1 must equal the rate at which heat is radiated from the shield to surface 2. 

It is advisable to wrap the entire apparatus with aluminum foil to avoid exposure to ultraviolet light. The reaction solution can be observed through a small hole in the aluminum foil which is shielded from the direct radiation of the lamp. 

The detector itself may be shielded from background y-rays by means of an annular shield of W or Pb, and absorbers in the form of appropriate metal foils are placed between the detector and the specimen. These reduce the intensity of the continuum of Bremsstrahlung radiation and also prevent back-scattered protons from entering the detector which would degrade the observed spectrum. 

The ratio is clearly pressure dependent in the lower stratosphere [02] and [M] are fairly large and /3 is small (due to absorption above the required wavelengths), so the dominant odd-oxygen species is ozone. At higher altitudes both [02] and [M] fall and the photolysis rate increases so that O is the dominant species in the atmosphere. The net flux of radiation in the band 240-290 nm is nearly zero at the surface of the Earth, which is then shielded from this radiation. 

Shielding Rule 3 Use available resources to shield your lungs against airborne contaminants (e.g., cover your mouth with a handkerchief) and shield your body from radiation (e.g., move behind a concrete wall). 

Nuclear Explosion Survival Rule 3 Get below ground if possible or move to the center of a large building before fallout arrives. Note that the ground and layers of solid barriers (e.g., brick, cinderblock, concrete) will shield against radiation from fallout. 

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