Binary fission

“ First, with regard to sexual propagation, we have already seen that this is by no means the only method of propagation among the multicellular organisms; and it now remains to add that, on the other hand, there is, to say the least, a suggestive foreshadowing of sexual propagation among the unicellular organisms. For although simple binary fission is here the more usual mode of multiplication, very frequently two (rarely three or more) Protozoa of the same species come together, fuse into a single mass, and thus become very literally “one flesh.” ”

“ The body substance is granular, with a spherical, sharply contoured nucleus and an accessory nuclear body. No vacuoles are present, but occasionally the endoplasm contains red blood corpuscles. The pseudopodia are hyaline, finger- or lobe-shaped, and are protruded either singly or in twos. Multiplication is by binary fission and by the formation of spherical cysts (15 μ to 20 μ in diameter) in which occurs successive division of the nuclei, ultimately forming ten to twelve roundish bodies each of which soon develops a flagellum. ”

“ When a neutron strikes the nucleus of uranium-235 (235U) or plutonium-239 (239Pu) , it may cause the nucleus to split into two roughly equal fragments, releasing neutrons and energy. This is the well-known process of neutron-induced fission, the method in which nuclear energy is produced in both reactors and bombs. [14] The most common uranium isotope, 238U, also breaks up by fission, but does so all by itself, without the need for any external neutrons. That process is spontaneous fission and it goes on at random, very much like radioactive decay. ”

“ Of the 200 million electron-volts released in fission, about 10 million go into gamma rays and neutrons created in the fission process itself. This energy contributes to the immediate and local radiation danger. Another 24 million electron-volts go into radioactivity of the fission products, and of this, about half go into neutrinos, which are neither dangerous nor useful; the other half is carried by electrons and gives rise to the delayed radioactive hazard. But the bulk of the energy, over 160 million electron-volts, goes into kinetic energy of the two primary fission fragments. ”

“ Occasionally the random quivering of a nucleus would bring about a shape that the nuclear interaction could not bring back to normal and the nucleus would then break apart. In a gram of ordinary uranium, there is a nucleus undergoing such “spontaneous fission” every 2 minutes on the average. Therefore, enough uranium need only be brought together to surpass critical size and it will explode within seconds, for the first nucleus that undergoes spontaneous fission will start the chain reaction. ”

“ A balance of the elements A and B cancels out and therefore we have the normal explosion experienced in Earth One."
"But how did it happen?"
"When the subcritical masses of uranium came together on Alamogordo Day, the fission started throughout the mass. Also present—we know now—is the capture of neutrons by unfissioned atoms which raise the element's mass, and the other fission products hitting this element raise its charge. Space-resonant elements resulted in those sub-microseconds of initial fission. ”

“ The nuclear processes during conjugation suggest the phylogenetic loss of a process of multiple fission into active gametes. As noted, in fission the meganucleus divides by direct constriction; each micronucleus by a mode of mitosis. The process of fission is subject in its activity to the influences of nutrition and temperature, slackening as the food supply becomes inadequate or as the temperature recedes from the optimum for the process. ”

“ Our early nuclear explosives have used fission. In the fission process a great array of radioactive products are formed, some of them intensely poisonous. More recently we have learned how to produce energy by fusion. Fusion produces fewer and very much less dangerous radioactivities. Actually the neutrons which are a by-product of the fusion reaction may be absorbed in almost any material and may again produce an assortment of radioactive nuclei. However, by placing only certain materials near the thermonuclear explosion, one may obtain a weapon in which the radioactivity is harmless. ”

“ An important feature of Fermi’s experiment is the large amount and variety of radioactivity that he found. The reason for this variety, as we now know, is that the fission process does not take place in a unique manner. The two primary fission fragments are very rarely of equal weight and charge. On the average the lighter fragment weighs about 90, and the heavier one about 140. Sometimes the lighter fragment will weigh as little as 75, and the heavier one as much as 160. As the weight varies, of course, so also does the charge. ”

“ The first large-scale application of thermonuclear energy was the so-called hydrogen bomb, or “H-bomb.” For a brief time an exploding fission bomb develops a temperature 28 of hundreds of millions of degrees Fahrenheit, hot enough to cause some light nuclei to fuse. In the hydrogen bomb, light nuclei of deuterium and/or tritium are exposed to this temperature during such a fission explosion. The resulting fusion of these nuclei causes the explosion to be hundreds of times more powerful than that of the fission device alone. ”

“ The larger yield nuclear weapons derive a substantial part of their explosive force from the fusion of heavy forms of hydrogen--deuterium and tritium. Since there is virtually no limitation on the volume of fusion materials in a weapon, and the materials are less costly than fissionable materials, the fusion, "thermonuclear," or "hydrogen" bomb brought a radical increase in the explosive power of weapons. However, the fission process is still necessary to achieve the high temperatures and pressures needed to trigger the hydrogen fusion reactions. ”

“ The calf is her 15th to be born in 15 years. The cow, believed about 20 years old, has been under observation by scientists, who found she suffered little apparent effect, although the fallout caused some hair to turn gray (see light patches on back) . Other cows in the herd died natural deaths.
When a nuclear device is detonated, the release of energy is due to the fission of uranium or plutonium atoms or to the fusion of hydrogen atoms. At the instant of fission, some 75 radionuclides, or fission products, are created. ”

“ This happens for the simple reason that nuclei tend to be more stable when they have an even number of neutrons (or protons) than when they have an odd number. U235, having an odd number of neutrons, is more eager to receive an additional neutron than 238, which already has an even number of neutrons. Consequently, the capture of a slow neutron by 235 almost always eventuates in the fission process; while in 238, the excess energy, introduced by the 65 neutron, is merely ejected from the nucleus in the form of a gamma ray, and U238 becomes U239. ”

“ From such arguments as these one concludes that Sr90 and Cs137 are the most important isotopes for the internal hazard from the world-wide fallout. One can be reasonably sure that there are no others of importance, because careful and extensive 107 research has not found significant amounts of any in our bodies. We need not fear that one has been overlooked, because the beta activity of the fission products is always easy to detect. ”

“ Of course, there was no great desire for a fearful explosion to get out of hand while the chain reaction was being studied. Before any bomb could be constructed, the mechanism of the chain reaction would have to be studied. Could a chain reaction capable of producing energy (for useful purposes as well as for bombs) be established? To test this, a quantity of uranium was gathered in the hope that a controlled chain reaction of uranium fission could be established. For that purpose, control rods of a substance that would easily absorb neutrons and slow the chain reaction were used. ”

“ Gemmation may be correlated with multiple nuclear fission in such a way that buds are formed over the whole body surface of the organism, which thereby undergoes a process of simultaneous multiple fission into numerous daughter-individuals. Rapid multiple fission of this kind is termed sporulation, and is a form of reproduction which is of common occurrence, especially in parasitic forms. ”

“ I was too close to the atom-rocket. My conductor screen grazed the warhead itself!
Its energies surged through the unstable elements in the warhead; a warning bell sprang into clamorous life. The group around me froze in their tracks, mouths open, faces mirroring fright and disbelief—and the frightful power of the strained atoms within the warhead began to grind toward nuclear fission! ”

“ The one per cent of argon found in the earth’s atmosphere comes almost entirely from the second reaction. These radioactivities are also interesting because appreciable amounts of potassium40 are always present in human tissue.
All nuclei at the heavy end of the periodic system are radioactive alpha emitters. Uranium, for example, has no stable isotopes; they all undergo alpha decay. But there is another 46 mode of spontaneous decay of uranium, which is much less frequent than alpha decay but is of much greater practical importance. This is the fission process. ”

“ This can, for obvious reasons, lead to serious instability in the overall system—most interesting systems cannot withstand the unbounded increase of any of their parameters without serious negative consequences. The basic engineering principles underlying the creation of nuclear weapons exploit this feature of positive feedback mechanisms: the destructive output of nuclear weapons results from the energy released during the fission of certain isotopes of (in most cases) uranium or plutonium. ”

“ Not all the radioactivity which is made in the explosion contributes to the fallout, either local or world-wide. Some of the radioactive fission fragments (gamma emitters) have such short half-lives [11] that they actually disintegrate before the bomb has disassembled. A great many others disintegrate in the first few minutes while the atomic cloud is rising. The energetic beta and gamma rays released in these early, rapid disintegrations are stopped in short distances and merely add to the havoc at the scene of the explosion. ”

“ One striking fact about uranium fission was the large amount of energy it released. In general, when a very massive nucleus is converted to a less massive one, energy is released because of the change in the mass defect, as Aston had shown in the 1920s. When the uranium nucleus breaks down through the ordinary radioactive processes to become a less massive lead nucleus, energy is given off accordingly. When, however, it breaks in two to become the much less massive nuclei of barium and krypton (or others in that neighborhood) much more energy is given off. ”

“ The positive electric charges within an atomic nucleus repel one another. In the most heavily charged nuclei this repulsion becomes so great that the nucleus can break into two parts, simultaneously releasing a considerable amount of energy. In the case of spontaneous nuclear fission the two parts are more or less equal in size. ”

“ But all these applications will use up only a vanishing 162 fraction of the fission products. Moreover, most of the biologically important elements are not produced in the fission of uranium. Many useful activities can be produced by neutron absorption in reactors. But among the fragments of uranium perhaps only radio-iodine has been put so far to direct physiological use.
Industry deals with less sensitive objects than living tissue. Therefore greater amounts of radioactive materials can be used here. And indeed radioactivity has done a great variety of jobs. ”

“ They tended to travel too far too soon and get outside the lump of uranium too easily. To produce a chain reaction that could be studied with some safety, the presence of a moderator was needed. This was a supply of small nuclei that did not absorb neutrons readily, but absorbed some of the energy of collision and slowed down any neutron that struck it. Nuclei such as hydrogen-2, beryllium-9, or carbon-12 were useful moderators. When the neutrons produced by fission were slowed, they travelled a smaller distance before being absorbed in their turn and the critical size would again be reduced. ”

“ That explosion was the first man-made release of atomic energy—a process we had known how to bring about for ages, but one we would never use. For we have learned the secret of limitless power without the transformation of mass into energy. Your way is the way of destruction, Martin Kirk; ours is exactly the opposite.
"For the first time, the leaders of Mythox knew the meaning of fear—fear that, once Earth's scientists had found the secret of nuclear fission they would go on to the one extreme forbidden throughout the Universe itself. ”

“ Atavistic giganticism. It's all very clearly explained in the micro-films. Pituitary giants they are, with the physical characteristics of primitives. Dawn men."
Sheldon rubbed his burning brow.
"If I had returned a hundred years in the future what you say would not have seemed incredible," he muttered, dazedly. "The radiations produced by atomic fission on an almost undreamed of scale might alter human genes, yes. ”

“ In fact, from Aston’s studies it could be seen that, mass for mass, nuclear fusion would produce far more energy than nuclear fission. This was particularly true in the conversion of hydrogen to helium; that is, the conversion of the individual protons of 4 separate hydrogen nuclei into the 2-proton—2-neutron structure of the helium nucleus. A gram of hydrogen, undergoing fusion to helium, would deliver some fifteen times as much energy as a gram of uranium undergoing fission. ”