Radiation

“ If we imagine a field of radiation to be enclosed within perfectly reflecting walls, then, provided there is no material substance in the field which can radiate and absorb, the constitution of the radiation in it may be any whatever, and it will remain permanent. ”

“ The loss by radiation can be very considerable under certain circumstances; 50 per cent. of the whole quantity of heat generally going that way, it is obvious that radiation deserves our full consideration. Particularly, an unequal radiation may be very injurious, such as takes place when a person is sitting or lying near a cold wall which is not covered by some bad heat-conductor, or near a window, etc.
On school-forms, the exposed sides of the first and last pupils are always more cooled than the sides directed toward their neighbors. ”

“ If the above view is correct then it would be possible to detect the effect of molecular strain due to visible or invisible radiation by the following more or less delicate methods. It is to be borne in mind that the effect of radiation is almost confined to the skin or outer layer of the substance. ”

“ For the accurate measurement of deviation, the effect produced by radiation on the receiver should undergo an abrupt variation. When the radiation passes from a dense to a light medium, at a certain critical angle of incidence, the radiation is totally reflected. ”

“ When the particles become continuous, the radiation can only affect the extremely thin layer of molecules on the surface, the mass in the interior being shielded by the outer conducting sheet; the molecular changes produced on the surface layer do not affect to any appreciable extent the conductivity of the mass. ”

“ Influence of previous History.—As regards the first, I have already shown in my previous paper [2] that a substance strained by radiation often exhibits opposite or reversal effects. Freshly powdered particles often show erratic results, but the effects become consistent after annealing; this often increases the sensibility also, by increasing the molecular mobility. Fresh particles are sometimes found to exhibit very little sensitiveness. ”

“ In radiation, the heated body gives rise to a motion of vibration in the aether, which is propagated equally in all directions, and is reconverted into heat when it encounters any obstacle capable of absorbing it. Thus radiation differs from conduction and convection in taking place most perfectly in the absence of matter, whereas conduction and convection require material communication between the bodies concerned. ”

“ To speak in the first instance of radiation, it will be clear to you that our surface is prevented from radiating heat directly toward the colder objects in our neighborhood, and that it can only radiate toward the covering materials, which receive this heat. By the laws of conduction and radiation the heat, which has radiated from the body into the clothes, has to travel through them by radiation and conduction, till, arrived at their outer surface, it can radiate thence toward colder objects, just as it would from the naked surface of the body. ”

“ 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. ”

“ 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. ”

“ Of course, gases do radiate heat and light under some circumstances, but the radiation seems to be produced either by chemical action, as in the flames coloured by metallic vapours, or by electric discharge, as in vacuum tubes, the arc or the electric spark. ”

“ Radiation strikes the receiving object from all of the points—in greatest intensity from points perpendicular and closest to the object, and in lesser intensity from the other points. Because so many points are producing radiant energy, the decrease in intensity with distance from a flame source is less than that from a line source and much less than that from a point source. The number of points from which radiation can be received also increases rapidly with the area of the radiating surface. ”

“ As soon as it is possible to associate with any given special kind and arrangement of emitting and absorbing bodies a state of radiation in the surrounding vacuum which is characterized by absolute stability, then this state can be no other than that of black radiation. ”

“ There is no doubt that the process which takes place in the emission of radiation from the radioactive elements is a transformation of the element, an explosion of the atoms accompanied by the emission either of double-charged helium atoms or of electrons, and the forming of the atoms of a new element. The energy of the rays is an internal atomic energy, freed by these transformations. ”

“ 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. ”

“ 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. ”

“ Quite analogous are the relations at the emission of a moving black surface. It was left by a certain amount of total relative radiation, which is equal to the true relative radiation and is increased or decreased by the amount of work performed by or against the radiation pressure, depending on whether the black surface is moving in the positive or negative sense. Only the true relative radiation stems from the heat reservoir of the moving body, by which our terminology may be justified. ”

“ In this investigation it is essential that the substance examined should be completely protected from all disturbances, such as mechanical vibration, &c., and only subjected to the action of radiation. The experimental difficulties are very great. If we take a strongly sensitive positive substance—say iron, the effect of the first flash of radiation (a diminution of resistance) is very great, and the subsequent relatively feeble reversal effects, unless carefully looked for, are liable to pass unnoticed. ”

“ In its broadest sense, radiation is any phenomenon spreading out from some source in all directions. Physically, such radiation may consist of waves or of particles. [3] Of the wave forms the two best-known are sound and electromagnetic radiations.
Sound carries very low concentrations of energy. This energy is absorbed by living tissue and converted into heat. Heat in itself can increase the mutation rate but the effect is a small one. The body has effective machinery for keeping its temperature constant and the gonads are not likely to suffer unduly from exposure to heat. ”

“ A measure of radiation dose—defined in terms of the amount of energy deposited per unit weight of irradiated material. A dose of 400,000 roentgens in living tissue deposits enough energy to raise the temperature by 1°C. A dose of only 400 roentgens in a human being will cause death fifty per cent of the time. ”

“ Jetefti's remarkably erudite Demonstration—following studies of cosmic radiation around various Words—studies of ionization, of stratospheric air currents, of polarization, of the uninterruptibility of streams of neutrons, gamma rays, alpha particles, electrons, photons, and other forms of radiation with which the Words had been surrounded, of the Heaviside Layer, etc., etc.—that no external (i.e., interplanetary) agency or intelligence had projected the Words on city skies. ”

“ Even if it were supposed that the radio-elements possess the property of absorbing the energy of some unknown type of radiation, which is able to pass through ordinary matter with little absorption, there still remains the fundamental difficulty of accounting for the peculiar radiations from the radio-elements, and the series of changes that occur in them. ”

“ If there were no hole the internal stream of radiation would be exactly that of a black body at the same temperature however perfect the reflecting power, or however low the emissive power of the walls, because the defect in emissive power would be exactly compensated by the internal reflection. ”

“ To avoid this difficulty, we want to imagine adiabatic changes of the radiation state in our cavity as of such kind, that a black body is present in the space surrounded at all sides by mirrors, yet whose capacity is so small, that its heat content can be neglected against the energy content of space . ”

“ For such a spontaneous change must involve loss of availability; and, beyond the wave-length of maximum energy in the spectrum, the temperature of a given density of radiation is greater the shorter its wave-length, as it is a function of that density and the wave-length alone such that greater radiation always corresponds to higher temperature. ”

“ In the case of the radiation from our fire, about 98 per cent of the whole emission consists of invisible rays; the body, therefore, which was most opaque to these triumphed as an absorber, though that body was a white one. ”

“ The more ion pairs produced in living matter, the greater the extent of biological damage. For this reason it is customary to describe radiation effects in terms of the number of ion pairs created per gram of living tissue in various parts of the body. Since each ion pair corresponds to an energy transfer of about 32 electron-volts, an alternative description may be given in terms of the amount of energy deposited. ”

“ 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. ”

“ The great principle of radiation, which affirms that all bodies absorb the same rays that they emit, is now a familiar one. When, for example, a beam of white light is sent through a yellow sodium-flame, produced by a copious supply of sodium-vapor, the yellow constituent of the white beam is stopped by the yellow flame, and, if the beam be subsequently analyzed by a prism, a black band is found in the place of the intercepted yellow band of the spectrum. ”

“ Matter, we believe, is gradually destroyed and its energy set free in radiation. Is there no counter-process by which radiation collects in space, evolves into electrons and protons, and begins star-building all over again? ”

“ 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. ”

“ With the emission of radiation it can go from stationary states with greater energy to others with less energy, ending its journey by remaining in the orbit which corresponds to the least possible energy. ”

“ The following experiment with a moderately negative substance (arsenic) and a moderately positive substance (osmium) will bring out this interesting peculiarity in a clear manner. The intensity of incident radiation may be varied in two ways; (1) by removing the radiator further and further from the receiver, or (2) by using polarised radiation, whose intensity may be varied by the rotation of an analyser. In the experiments to be described, the first method was adopted. ”

“ Some types of radiation—those made up of comparatively large particles, for instance—are more effective in producing ions and bring about molecular changes with greater ease than do electromagnetic radiations delivering equal energy to the body. Thus if 1 rad of alpha particles is absorbed by the body, 10 to 20 times as much biological effect is produced as there would be in the absorption of 1 rad of X rays, gamma rays, or beta particles. ”

“ Ionizing radiation in low intensities is part of our natural environment. Such natural radiation is referred to as background radiation. Part of it arises from certain constituents of the soil. Atoms of the heavy metals, uranium and thorium, are constantly, though very slowly, breaking down and in the process giving off alpha rays, beta rays, and gamma rays. These elements, while not among the most common, are very widely spread; minerals containing small quantities of uranium and thorium are to be found nearly everywhere. ”