Uranium-235

“ 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. ”

“ Highly enriched uranium.—The term `highly enriched uranium' has the meaning given that term in section 3102 (4) . `` (4) Highly enriched uranium of weapons origin.—The term `highly enriched uranium of weapons origin' means highly enriched uranium that— `` (A) contains 90 percent or more uranium-235; and `` (B) is verified by the Secretary of Energy to be of weapons origin. ”

“ The much scarcer, fissionable isotope of uranium, U-235, has a half-life of 700 million years, indicating that its present abundance is only about 1 percent of the amount present when the solar system was born.
Note 5: Oxygen, Ozone and Ultraviolet Radiation
Oxygen, vital to breathing creatures, constitutes about one-fifth of the earth's atmosphere. It occasionally occurs as a single atom in the atmosphere at high temperature, but it usually combines with a second oxygen atom to form molecular oxygen (O2) . The oxygen in the air we breathe consists primarily of this stable form. ”

“ Nuclear fuel even today is no more expensive than conventional fuel in many parts of the United States. Nuclear fuel is neither heavy nor bulky and can be therefore transported easily. In those parts of the world where ordinary fuel is expensive, nuclear energy will soon become of great importance. Furthermore, we shall learn to use most of the energy in uranium rather than just the part contained in its rare and valuable isotope, U235. ”

“ One only has to add a neutron to common U238 to get radioactive U239. In the course of time this decays into plutonium. This element can be used like U235: It produces fission, a great amount of energy and enough neutrons to keep the process going. We shall also learn to extract energy from other nuclear fuels. Thorium acts like uranium, while deuterium can give energy by building up bigger nuclei rather than breaking them into smaller pieces. Therefore the source of energy will be universally available and quite inexpensive. ”

“ Natural uranium contains U235 in the ratio of 1 part to 139 of U238. It was hoped at first that this concentration would be sufficient to make a chain reaction, and that the expensive enrichment processes could be avoided. This seemed possible because at energies of a fraction of an electron-volt the neutrons are much more easily caught by U235 than by U238, which compensates for the low concentration. Actually neutrons are slowed down until their energy is as low as the energy of all other particles participating in the general agitation caused by the temperature. ”

“ 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. ”

“ This lever has a universal joint and connects with a hidden chamber, and when pulled will catapult the annihilated components of a small quantity of uranium in any direction we desire. The release of the slumbering energy of this uranium will produce an explosion of proportions beyond the wildest dreams of engineers—perhaps, one great enough to throw the Earth out of its orbit! ”

“ 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. ”

“ 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. ”

“ Whereas, the DU weapons not only penetrate armor and other hardened targets, but also burst into flames releasing quantities of aerosolized uranium particles into the environment that are easily carried by wind or water and are easily resuspended, blowing radioactive contamination to locations quite distant from battlefield locations ”

“ One isotope of plutonium, plutonium-239, which resulted from the absorption of a neutron by a 238U nucleus and the emission of two beta particles, was discovered to be as fissionable as 235U and hence theoretically just as feasible for a bomb. Since plutonium is chemically different from uranium, it offered the tremendous advantage that it could readily be concentrated by conventional chemical techniques.
The way to manufacture usable amounts of plutonium, an element that had never before been detected on earth, is to expose uranium to a very intense neutron bombardment. ”

“ However, the neutrons are made in the fission process with an energy of about a million electron-volts. Before they slow down sufficiently, they must pass through a stage in which their energy is about 7 electron-volts. In the neighborhood of this energy, it happens that the U238 has an extremely high probability for capturing a neutron and changing into U239. Near some other energies, similar though smaller absorption hurdles must be passed. Therefore natural uranium by itself 66 cannot be used to make a chain reaction. ”

“ Now you have lost completely, Hohmann, for the radiation from that paper when bombarded with the plutonium radiation, produces a whole string of secondary radioelements in your offices, in your desks, in your bodies, and in your air. The ash from burning is still hot, Hohmann, and the trucks that will carry the deadly paper will be as deadly. Your very country will be subject to slow fission if you start another uranium pile for several hundred years. ”

“ The range of the plutonium radiation is unknown, but it is great enough to bathe the entire country. You will find that most government offices are bulging with reams and reams of correspondence, many of which are over the critical mass. Nothing happens until someone turns on a plutonium-producing uranium pile, lets it run for a few hours, and the accumulation of plutonium starts. Right now, Hohmann, you have about four hours before most of your government offices go sky-high—from their own red tape. ”

“ 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”. ”

“ This was the day and moment when the world entered the “nuclear age”. For the first time, mankind had constructed a device in which the nuclear energy being given off was greater than the energy poured in. Mankind had tapped the reservoirs of nuclear energy and could put it to use. Had Rutherford lived but 6 more years, he would have seen how wrong he was to think it could never be done.
The people of earth remained unaware of what had taken place in Chicago and physicists continued to work toward the development of the nuclear bomb.
Enriched uranium was successfully prepared. ”

“ The lead-210 will then decay with its 22-year half-life.”
The radioactive series that starts with uranium is like a series of lakes connected by waterfalls. As long as uranium, the big one on top, has water in it, the others will be full and the falls will keep flowing. ”

“ But, surrounded by a shield through which no neutron could escape, any mass of material on earth would become an atomic pile!
A single molecule of uranium in any mass of rock will sooner or later disintegrate, giving off high-speed neutrons. Normally they travel indefinitely and are harmless. Some go up into the air and may ionize a single molecule. Some may find a fissionable atom and disrupt it. ”

“ 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. ”

“ They're doing with more or less of a rush what all the elements are doing at their leisure. A single ounce of uranium contains about the same amount of energy that could be produced by the combustion of ten tons of coal—but it won't let the energy go. Instead it holds on to it, and the energy leaks slowly, almost imperceptibly, away, like water from a big reservoir tapped only by a tiny pipe. 'Atomic energy' Rutherford calls it. Every element, every substance, has its ready to be touched off and put to use. ”

“ The HEU Agreements provide for the conversion of approximately 500 metric tons of highly enriched uranium contained in Russian nuclear weapons into low-enriched uranium for use as fuel in commercial nuclear reactors. ”

“ Iraq’s long-standing civil nuclear power programme is limited to small scale research. Activities that could be used for military purposes are prohibited by UNSCR 687 and 715. Iraq has no nuclear power plants and therefore no requirement for uranium as fuel. Iraq has a number of nuclear research programmes in the fields of agriculture, biology, chemistry, materials and pharmaceuticals. None of these activities requires more than tiny amounts of uranium which Iraq could supply from its own resources. ”

“ The nuclear force is so short-range, it barely reaches from end to end of a large nucleus like that of uranium. Left to itself, it holds together most of the time, but with the added energy of an entering neutron, we might imagine shock waves going through it and turning the nucleus into something like a quivering drop of liquid. Sometimes the uranium nucleus recovers, keeps the neutron, and then goes on to beta-particle emission. And sometimes the nucleus stretches to the point where the nuclear force doesn’t quite hold it together. ”

“ Then 2 beta particles are given off so that the thorium-233 becomes first protactinium-233 and then uranium-233.
If a thorium shell surrounds a nuclear reactor, fissionable uranium-233 is formed within it and is easily separated from the thorium. In this way, thorium is also added to the list of earth’s potential nuclear fuels. [4]
If all the uranium and thorium in the earth’s crust (including the thin scattering of those elements through granite, for instance) were available for use, we might get up to 100 times as much energy from it as from all the coal and oil on the planet. ”

“ You know, most of the wars they've been fighting, lately, on the Europo-American Sector have been, at least in part, motivated by rivalry for oil fields. But now that the Europo-Americans have begun to release nuclear energy, fissionables have become more important than oil. In less than a century, it's predicted that atomic energy will replace all other forms of power. Mineral Products Syndicate wanted to get a good source of supply for uranium, and your Proto-Aryan Sector franchise was worth grabbing. ”

“ 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. ”

“ Teena asked.
“They don’t shove them in with their bare hands,” Eddie said, trying not to show exasperation. “They use long holders to push the small chunks of material into the holes in the reactor. Then, as those uranium atoms keep splitting up and shooting particles around inside of the pile, some of them smack into the chunks of material, and stick there. Most elements will soak up radiation, just like a sponge soaks up water.” ”

“ The uranium bomb was a simple design and scientists were confident it would work without testing. The plutonium bomb worked by compressing the plutonium into a critical mass which sustains a chain reaction. The compression of the plutonium ball was to be accomplished by surrounding it with lens-shaped charges of conventional explosives. They were designed to all explode at the same instant. The force is directed inward, thus smashing the plutonium from all sides. ”