Infrared radiation

“ Electromagnetic radiation comes in a wide range of energies, with visible light (the best-known example of such radiation because we can detect it directly and with great sensitivity) about in the middle of the range. Electromagnetic radiations less energetic than light (such as infrared waves and microwaves) are converted into heat when absorbed by living tissue. The heat thus formed is sufficient to cause atoms and molecules to vibrate more rapidly, but this added vibration is not usually sufficient to pull molecules apart and therefore does not bring about chemical changes. ”

“ A total of approximately 100 000 infrared spectra, many of small regions on the disk, were obtained by IRIS. These spectra generally show hydrogen, helium, methane, ammonia, phosphine, ethane, and acetylene. In addition, excellent spectra were obtained in “hot spots,” regions in which breaks in the upper clouds permit radiation from deeper layers to escape. (The hot spots generally correspond to dark brown regions on photographs of the planet.) IRIS measured temperatures in the hot spots up to -13° C but no higher; apparently this temperature corresponds to the top of a deeper cloud deck. ”

“ One of the results of all this is that every month new uses of radioisotopes are developed.
More persons are trained every year in methods of radioisotope use and more manufacturers are producing and packaging radioactive materials. This booklet tells some of the successes achieved with these materials for medical purposes.
What Is Radiation?
Radiation is the propagation of radiant energy in the form of waves or particles. It includes electromagnetic radiation ranging from radio waves, infrared heat waves, visible light, ultraviolet light, and X rays to gamma rays. ”

“ The electromagnetic waves of radiant energy move only along straight paths. Hence, the intensity of radiation received depends on the angle of the incoming radiation and the distance from the source. Radiation perpendicular to the receiving surface is most intense. For a point source of radiation the intensity decreases inversely with the square of the distance from the source. ”

“ No certain evidence has yet been obtained that any body can be made radio-active by exposure to Röntgen rays or cathode rays. A metal exposed to the action of Röntgen rays gives rise to a secondary radiation which is very readily absorbed in a few centimetres of air. ”

“ In a complex way, the amount of thermal radiation reflected depends on the characteristics of the surface of the substance, the radiation wavelength, and the angle at which the radiation strikes the surface. In general, however, smooth, light-colored surfaces reflect more radiation than do dark, rough surfaces. A highly polished, smooth surface such as a mirror or chrome on a car, reflects a large part of the thermal radiation, but a black-topped road surface reflects very little. ”

“ The radio-active energy which accumulates in the radium tends to become dissipated in two different ways:— (1) By radiation (rays both charged and uncharged with electricity) ; (2) by conduction, i.e., by gradual transmission to surrounding bodies in a medium of gases and liquids (production of an emanation and transformation into induced radio-activity) .
The loss of radio-active energy, both by radiation and by conduction, increases with the amount of energy accumulated in the radio-active body. ”

“ If we take into account the entire range of radiation there is hardly a substance which is not, in this sense, coloured. In the spectrum of radiation transmitted through glass, for example, two broad absorption-bands would be observed, one in the ultra-violet, and the other in the infra-red, the electric and the visible rays not being absorbed to any great extent. ”

“ In these experiments it is the radio-active energy accumulated in the gas that maintains the activity of the walls. If the gas be withdrawn and a vacuum caused in the enclosure, we have found that dissipation of activity at once occurs in the rapid method; the intensity of radiation being reduced to one-half in twenty-eight minutes. ”

“ That is what radium does to that kind of glass. You see, if radium exists in a gram of inactive matter only to the extent of one in ten-thousand million parts its presence can be readily detected by this radioscope, and everything that has been rendered radioactive is the same. Ordinarily the air between the gold leaves is insulating. Bringing something radioactive near them renders the air a good conductor and the leaves fall under the radiation. ”

“ The experiments are not easily carried out, except with very intense radio-active sources, because, independently of the absorption by the air, the action upon a given receiver varies inversely as the square of the distance from a source of small dimensions. This radiation, which travels a long distance in the case of radium, comprises rays of the cathode kind and rays which are undeflected ”

“ The rays from the active substances carry off energy in a very concentrated form, and this energy is dissipated by the absorption of the rays in matter. The rays might be expected to cause a disintegration of the atoms of inactive matter on which they fall and thus give rise to a kind of radio-activity. This effect has been looked for by several observers. Ramsay and W. T. Cooke [361] state that they have noticed such an action, using about a decigram of radium as a source of radiation. ”

“ Although these particles are sustained by the gases of the sun, and are associated in aggregations which form the dazzling clouds of the photosphere, yet each one of them, in so far as its individual radiation is concerned, ought to be regarded as a solid body. The radiation from the sun is, therefore, essentially not the radiation from an incandescent gas; it is the radiation from a glowing solid. This is the reason why the solar spectrum is of the continuous type. ”

“ Of course, upon this foundation one can calculate the values and , when one assumes that a moving body is emanating waves, whose amplitude is the same as in the stationary state, while the density of the radiation energy is inversely proportional to the square of the wavelength. ”

“ One can foresee the possibility of establishing mechanics upon the dynamics of small material centers charged and in motion.
α-Rays.—The α-rays of radium have very little power of penetration. A piece of aluminium foil a few hundredths of a millimeter in thickness absorbs them almost completely. They are also absorbed by the air, and cannot penetrate air at the atmospheric pressure to a greater distance than 10 cm. The α-rays form the most important part of the radiation of radium, provided we measure the radiation by the amount of ionization which it produces in the air. ”

“ Any directed quality in radiant energy increases its effective temperature. Splitting a beam into two at s reflecting and refracting surface diminishes the temperature of each part; it is true that if the reflecting surface were non molecular the operation could be reversed, but actually the reversed rays would encounter the reflecting molecules in different collocations, and could not (§ 11) recombine into the same detailed phase-relations as before. The direct solar radiation falling on the Earth is almost completely convertible into mechanical effect on account of its very high temperature ”

“ Thus, the invisible waves of our filtered electric beam with which incandescence has been produced, may be regarded as generating synchronous vibrations in the platinum on which they impinge; but once these vibrations attain a certain amplitude, the mutual jostling of the atoms would produce quicker tremors, and the light-giving waves would follow as the necessary progeny of the heat-giving vibrations. From the very brightness of the light of some of the fixed stars we may infer the intensity of the dark radiation, which is the precursor and inseparable associate of their luminous rays. ”

“ In my preliminary experiments on the determination of the index of refraction of various substances for electric radiation, I used a single semi-cylinder of the given substance; the electric ray was refracted from the denser medium into air, and at the critical angle of incidence it underwent total reflection. The experiment was repeated with two semi-cylinders separated by a parallel air-space. With light waves an extremely thin air-film is effective in producing total reflection. ”

“ The rays which it emits prior to redness are all invisible rays, which can warm the hand but can not excite vision. When the temperature of the wire is raised to whiteness these dark rays not only persist, but they are enormously augmented in intensity. They constitute about 95 per cent, of the total radiation from the white-hot platinum wire. They make up nearly 90 per cent, of the emission from a brilliant electric light. You can by no means have the light of the carbons without this invisible emission as an accompaniment. ”

“ It is now a commonplace that chemical action, colour sensation and heat are merely different effects of one and the same kind of radiation, the particular effect produced in each case depending on the frequency and intensity of the vibration, and on the nature of the substance on which it falls. When radiation is completely absorbed by a black substance, it is converted into heat, the quantity of heat produced being equivalent to the total energy of the radiation absorbed, irrespective of the colour or frequency of the different rays. ”

“ If the earth is supposed to be in a state of thermal equilibrium in which the heat lost by radiation is supplied from radio-active matter, there must be an amount of radio-active matter in the earth corresponding to about 270 million tons of radium. If there were more radium than this in the earth, the temperature gradient would be greater than that observed to-day. ”

“ It is only the presence of material bodies that by their continued emission and absorption can transform the surrounding radiation towards the unique constitution which corresponds to their temperature. We can define the temperature of an isolated field of radiation, of this definite ultimate constitution, to be the same as that of the material bodies with which it would thus be in equilibrium. ”

“ In recent years, doubt as to the necessity for assuming the existence of an ether has been expressed by some who claim that it is sufficient to attribute the power of transmitting radiation to space itself. ”

“ We have, therefore, indubitable proof in all these experiments that we have something proceeding from the radiator which is capable of being reflected or refracted just like the rays of sound or ripples on the surface of water; and, moreover, we find that this electric radiation passes through some substances but not through others. There is, therefore, a strong presumption that we are here dealing with something which is similar in nature to light, although it cannot affect the eye. In order that we may complete the proof we must show that this radiation is susceptible of interference. ”

“ The extreme richness of the electric light in invisible rays of low refrangibility was demonstrated, one-tenth only of its radiation consisting of luminous rays. The deadness of the optic nerve to those invisible rays was proved, and experiments were then added, to show that the bright and the dark rays of a body raised gradually to intense incandescence, are strengthened together; that to reach intense white heat, intense dark heat must be generated. A sun could not be formed, or a meteorite rendered luminous, on any other conditions. ”

“ The radiations, consisting of definite narrow bright bands in the spectrum, that are characteristic of the gaseous state in which each molecule can vibrate freely by itself, are usually excited by electric or chemical agency; thus there is no ground for assuming that they always constitute true temperature radiation. The absorption of these radiations by strata of the same gases at low temperatures seems to prove that the unaltered molecules themselves possess these free periods, which do not, therefore, belong specially to dissociated ions. ”

“ Atmospheric transmittance, solar constant, solar flare activity, solar particle detection, Earth radiation budget wave receiver technology is rapidly advancing to submillimeter wavelengths which will enable the measurement of many additional minor atmospheric constituents that play a part in radiative transfer processes. ”

“ If, instead of the platinum wire, the earth itself were raised to incandescence, the obscure radiation which it now emits would continue to be emitted. To reach incandescence the planet would have to pass through all the stages of non-luminous radiation, and the final emission would embrace the rays of all these stages. There can hardly be a doubt that from the sun itself, rays proceed similar in kind to those which the dark earth pours nightly into space. In fact, the various kinds of obscure rays emitted by all the planets of our system are included in the present radiation of the sun. ”

“ The upper atmosphere covers the range of 15 to 150 km in altitude. Absorption and emission of radiation occur over a wide range of the electromagnetic spectrum at these heights. Satellite systems presently exist or are in the planning stages which perform high resolution passive radiometry measurements in both down-looking and limbsounding modes of vibrational (IR) and rotational (mm) molecular transitions. Limb-sounding microwave techniques will for tile first time allow study on a continuous global scale since spectral lines are observed in emission. ”