Nuclear fission

“ Nuclear reactors generate energy with the help of nuclear fission. Every time a fission occurs we are left with radioactive by-products. It is most important to prevent the uncontrolled escape of these fission products from the reactor. Fortunately the dangerous products can be retained in the reactor—if the machine has been constructed and operated with reasonable care. ”

“ Only a few, relatively rare, naturally occurring substances -- primarily Uranium-235 -- can maintain the nuclear fission chain reaction necessary for operation of these [p1083] reactors. There are thus severe constraints on the long run potential of nuclear energy for generating electricity unless new nuclear fuel is "artificially" produced. ”

“ 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. ”

“ In the years devoted to the development and construction of a nuclear weapon, scientists and technicians expanded their knowledge of nuclear fission and developed both the gun-type and the implosion mechanisms to release the energy of a nuclear chain reaction. ”

“ 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. ”

“ 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. ”

“ It has been estimated that an attack on U.S. population centers by 100 weapons of one-megaton fission yield would kill up to 20 percent of the population immediately through blast, heat, ground shock and instant radiation effects (neutrons and gamma rays) ; an attack with 1,000 such weapons would destroy immediately almost half the U.S. population. These figures do not include additional deaths from fires, lack of medical attention, starvation, or the lethal fallout showering to the ground downwind of the burst points of the weapons.
Most of the bomb-produced radionuclides decay rapidly. ”

“ Both the local and worldwide fallout hazards of nuclear explosions depend on a variety of interacting factors: weapon design, explosive force, altitude and latitude of detonation, time of year, and local weather conditions.
All present nuclear weapon designs require the splitting of heavy elements like uranium and plutonium. The energy released in this fission process is many millions of times greater, pound for pound, than the most energetic chemical reactions. ”

“ 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. ”

“ 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. ”

“ By arguing in this way one finds that for each megaton of fission energy which escapes from the test site in the world-wide fallout the lives of approximately four hundred persons would be shortened by leukemia or bone cancer. Under present conditions of testing, roughly one half of the fission products are deposited as close-in fallout in and near the test site. Per megaton of fission energy exploded, therefore, perhaps 200 persons may get leukemia or bone cancer. ”

“ The reactor is charged with radioactive fission products and some other radioactive substances produced by neutron absorption. Any accident which will allow even a portion of these products to escape into the air will endanger people at a considerable distance in the downwind direction. One reason why reactors can be dangerous is that in protracted operation of the reactor, fission products which have longer lives accumulate. It is precisely these longer-lived products which are more dangerous because they have a better chance to find their way into the human body. ”

“ 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. ”

“ 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. ”

“ The nature of the surface, whether it is soil or water, also plays a role. If the explosion has taken place right on the ground, on a soil surface, a lot of big, heavy dirt particles become incorporated into the fireball and begin to fall under the action of gravity even before the cloud stops rising. This fallout continues for a period of several hours to perhaps a half day. At the same time some of the radioactive fission products which have adhered to these dirt particles also fall out. ”

“ Enemy realization of an impending defeat may be preceded by disparagement of the importance of the area in which the defeat is to take place, or by description to the home audience of the enormous strength which enemy forces face at that particular place. Enemy action—when the enemy is security-minded—may be anticipated from his complete silence on something which he would normally talk about. It must have seemed odd that the Americans stopped talking about nuclear fission altogether, when prewar years had seen a certain number of news items on the subject in the New York press each month. ”

“ 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. ”

“ The ortho-history books were clear on one fact: Venus had been destroyed in the War of Annihilation by means of a hydrogen-chain reaction, the most deadly atom blast known. Atoms of hydrogen, under the influence of gamma-particle bombardment, coalesced to form atoms of helium—and all the incalculable power represented by the odd fraction of mass left over was released in the form of free energy.
But the atom-rocket before me seemed to be nothing more than a simple nuclear-fission affair! Where were the photon-exciters? ”

“ 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. ”

“ President, lies in the spiritual. Every race on every inhabited planet is given the intelligence and desire to evolve upward spiritually but they do not always succeed. A time limit is set on this so that the inhabitants of each planet arrive finally at an evolutionary crisis."
The President thought of nuclear fission, the atom bomb, mankind's incredible progress over the last two hundred years. "And you have come to aid us in spiritual development?" ”

“ Jars said, "and with this particular planet we're discussing, it can be a dangerous attitude."
"So?" Deering said, nudging me. "And could I ask why?"
"Ask it."
"I ask."
"You've recorded the state of their development. They have, among other things, achieved nuclear fission."
"So? In the fourth grade we are teaching nuclear fission."
"We are a scientific people. They haven't been, until very, very recently. You have noted, I hope, their first extensive use of this new discovery?"
"Hero—Helo—" Deering shrugged. "My memory."
"Hiroshima," Jars supplied. "Love—, my friend?" ”

“ If a chain reaction could be started in a sizable piece of uranium, unimaginable quantities of energy would be produced. Just 1 gram of uranium, undergoing complete fission, would deliver the energy derived from the total burning of 3 tons of coal and would deliver that energy in a tiny fraction of a second.
Szilard, who had come to the United States in 1937, clearly visualized the tremendous explosive force of something that would have to be called a “nuclear bomb”. ”

“ 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. ”

“ You hear a lot of talk these days about secret weapons. If it's not a new wrinkle in nuclear fission, it's a gun to shoot around corners and down winding staircases. Or maybe a nice new strain of bacteria guaranteed to give you radio-active dandruff. ”

“ All that mattered was that unless the Blazers were stopped immediately our world was finished. Those fission-hungry fiends would strip us to the last erg of our nuclear energy—and to a world geared to atomic power that meant the end. ”

“ The world appeared to have far greater sources of energy than had been expected. The “fossil fuels”—coal, oil and natural gas—were being used at such a rate that many speculated that the gas and oil would be gone in decades and the coal in centuries. Was it possible that uranium might now serve as a new source that would last indefinitely?
It was rather disappointing that it was uranium-235 which underwent fission, because that isotope made up only 0.7% of the uranium that existed. ”

“ 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 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. ”