Radiation energy, absorbed/emitted

Dose is related to the amount of radiation energy absorbed by people or equipment. If the radiation comes from a small volume compared with the exposure distance, it is idealized as a point source (Figure 8.3-4). Radiation source, S, emits particles at a constant rate equally in all directions (isotropic). The number of particles that impact the area is S t Tr where Tr is a geometric effect that corrects for the spreading of the radiation according to ratio of the area exposed to the area of a sphere at this distance i.e. the solid angle - subtended by the receptor (equation 8.3-4). 

Another way of achieving polymerisation at low temperatures is by using ionising radiation from gamma rays emitted by cobalt-60. The radiation energy absorbed by the monomer results in the production of free radicals. The radiation method does not require initiators or promoters. On the other hand, the cost of radiation source is high and polymerisation rate may be low [11]. 

Velocity of electromagnetic radiation Energy of a photon of electromagnetic radiation Energy absorbed or emitted during an electron transition Velocity of hght in a medium... 

The field of science that studies the interaction of electromagnetic radiation with matter is known as spectroscopy. Spectroscopic studies on the wavelength, the intensity of the radiation absorbed, emitted, or scattered by a sample, or how the intensity of the radiation changes as a function of its energy and wavelength, provide accurate tools for studying the composition and structure of many materials (Davies and Creaser 1991 Creaser and Davies 1988). 

Many compounds are capable of absorbing uv radiation and subsequently emitting radiation of a longer wavelength, either instantly (fluorescence) or after a time delay (phosphorescence). Usually, the fraction of the absorbed energy that is re-emitted is quite low, but for a few compounds values of 0.1-1 are obtained, and such compounds... 

Radiation is not emitted continuously, but is emitted in small bundles called photons. The energy of a photon is dependent on the wavelength of the radiation. When a photon of radiation is absorbed into a metal such as the cathode (negative plate) of the UV tube, the energy of the photon is imparted to an electron within the metal, causing it to leave the surface of the metal and be drawn toward the anode (positive plate). The energy that the electron must have to leave the metal is called the work function of the metal. The sensitivity range of the radiation detector is dependent upon the work function of the metal used in the cathode. 

Since the earth has temperature, it emits radiant energy called thermal radiation or planetary infrared radiation. Measurements by satellites show an average radiant emission from the earth of about 240 watts per square meter. This is equivalent to the radiation that a black body would emit if its temperature is at -19°C (-3°F). This is also the same energy rate as the solar constant averaged over the earth s surface minus the 30% reflected radiation. This shows that the amount of radiation emitted by the earth is closely balanced by the amount of solar energy absorbed and since the earth is in this state of balance, its temperature will change relatively slowly from year to year. 

If more solar energy is absorbed than infrared radiation emitted, the earth would warm and a new equilibrium would appear. But, if the earth had more clouds, it would reflect more solar radiation and absorb less. This would have a cooling effect on the planet, lowering the amount of infrared radiation that is escaping to space to balance the lower amount of absorbed solar energy. The earth s radiant energy balance today is 240 watts per square meter. 

Experimental spectra are usually presented as plots of the intensity of (absorbed, emitted, reflected, or scattered) radiation versus the photon energy (in eV), the wavelength (in nm) or the wavenumber (in cm ). Using Equation (1.1), useful interconversion equations between these different units can be obtained ... 

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