Radioactive decay

“ Unlike physical "systems"--bacteria, animals, men and stars--unstable isotopes do not individually have a predictable life span. There is no way of forecasting when a single unstable nucleus will decay.
Nevertheless, it is possible to get around the random behavior of an individual nucleus by dealing statistically with large numbers of nuclei of a particular radioactive isotope. In the case of thorium-232, for example, radioactive decay proceeds so slowly that 14 billion years must elapse before one-half of an initial quantity decayed to a more stable configuration. ”

“ To say that a given nucleus has one chance in a hundred of decaying in the next second means that out of some large number (say 100 million) of such radioactive nuclei, one per cent (one million) will decay in the next second. But it is absolutely impossible to say beforehand which nuclei will be the ones to decay. A particular nucleus may decay immediately or only after some very long time. The collection as a whole, however, will always do the expected thing. ”

“ 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. ”

“ 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. ”

“ Different radioactive species have different half-lives. Many are only a small fraction of a second; some are billions of years. N16 decays to O16 (plus an electron and a neutrino) with a half-life of about eight seconds. A free neutron decays into a proton, an electron, and a neutrino with a half-life of 13 minutes. Strontium with weight 90 (Sr90) undergoes a beta decay with a half-life of 28 years. (This is an isotope that is not found anywhere in nature, but is made in fairly large quantities in the fission process.) ”

“ It works, in effect, like the upper chamber of an hourglass. Mathematically it is written:
N = N0e-λt
where N = the number of radioactive atoms present in the system now, N0 = the number that was present when t = 0, (in other words, at the time the clock started) , e = the base of natural (or Napierian [8] ) logarithms (the numerical value of e = 2.718 ...) , λ (lambda) = the decay rate of the radioactive material, expressed in atoms decaying per atom per unit of time, t = the time that has elapsed since the origin of system, expressed in the same units. ”

“ When a nuclear weapon explodes near the ground, great quantities of pulverized earth and other debris are sucked up into the nuclear cloud. There the radioactive gases produced by the explosion condense on and into this debris, producing radioactive fallout particles. Within a short time, these particles fall back to earth--the larger ones first, the smaller ones later. On the way down, and after they reach the ground, the radioactive particles give off invisible gamma rays--like X-rays--too much of which can kill or injure people. These particles give off most of their radiation quickly ”

“ These facts are important because they determine the magnitude and the character of the danger when the radioactivity finally falls out of the cloud and is deposited on the surface of the earth. Those radioactive particles which disintegrate while still in the cloud need not worry us since this radiation can have no effect on living organisms that may be underneath. Provided that the cloud is more than a few hundred feet above the ground, the beta and gamma rays released in these disintegrations merely dissipate their energy in ionizing the air. ”

“ A better way to appreciate the danger from fallout is to compare it with other more familiar dangers. Such a comparison can be made with the natural background of cosmic rays and radioactivity in the earth and in our own bodies.
We are constantly and inescapably exposed to this radiation. Our ancestors have been exposed to it. The human race has evolved in such a radioactive environment. Moreover, the biological effects from different kinds of radiation can be compared in a meaningful way in terms of roentgens. Therefore the danger from Sr90 is not unknown in every respect. ”

“ Particularly significant studies have been conducted of the absorption of radionuclides by plants and animals living on nearby reefs and islands, and of both lateral and vertical diffusion rates of elements in the open ocean. [8]
The 1954 nuclear test at Eniwetok Atoll produced heavier-than-expected local radioactive fallout. Since then, both 24 American and Japanese scientists have studied water-mass movement rates, using the fallout radionuclides strontium-90 and cesium-137 themselves as tracer elements. ”

“ In the beginning of the Atomic Era, the Deadly Radiations existed. They still exist, but they are no longer deadly, because all life on this planet has adapted itself to such radiations, and all living things are now immune to them."
"And Hradzka has returned to a time when such immunity did not exist? But would that not be to his advantage?"
"Remember, General, that man has been using atomic energy for ten thousand years. Our whole world has become drenched with radioactivity. The planet, the seas, the atmosphere, and every living thing, are all radioactive, now. ”

“ A reactor accident conceivably could add a unique hazard since neutron radiation might change the normally stable, nonradioactive atoms in the bodies of nearby workers into radioactive ones. Even gold or silver fillings in their teeth might become radioactive. ”

“ 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. ”

“ 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. ”

“ The Radioactivity Induced by Radium and the Emanation from Radium.—When a solid salt of radium is placed in a closed space filled with air, the interior walls of the closed space and all solids in it become radioactive. We may, for example, place inside the space a plate of any solid, leave it there a certain time, and then remove it to study its activity. It is found that the activity of the plate increases at first according to the length of its stay in the space, but that it reaches a limiting value after a sufficiently long time. ”

“ Fallout radioactivity is assessed as a potential specific hazard to human populations.
2. Conditions created by fallout are examined for their potential long-term ecological significance.
3. Radionuclides introduced into the environment by nuclear tests, reactor operations, or other means are used as trace materials in basic studies in biological systems.
4. Radioactive forms of minerals and nutrients are deliberately introduced into biosystems—in measured amounts and under conditions of control—for studies of metabolic cycles and rates of flow of energy and nutrition. ”

“ After the storage period, the gas is pumped into an array of instruments known as a low-background PROPORTIONAL COUNTER, and its radioactivity is determined. This is an involved process. First there is the matter of the BACKGROUND COUNT.
The background count of an instrument is the number of pulses (counts) it will give per unit time when there is no radioactive sample in it. These counts are caused by cosmic rays, by radioactive contamination always found in the vicinity of the counter, or by any contamination inside the instrument. ”

“ Life on earth evolved amid constant exposure to ionizing [3] radiation, from the earth itself and from space, known as 4 background radiation. Therefore environmental studies must be conducted in relation to, and with understanding of, background radioactivity.
This Pacific Ocean coconut crab, member of a family that usually sticks to tide-covered beaches, depends on coconut trees for its food.
Of some 340 kinds of atoms that have been found in nature, about 70 are radioactive. ”

“ One of these tests involved the detonation of an atomic device under water, in the heart of the atoll’s aquatic circulatory system. Bikini also was used for 5 years, from 1954 through 1958, for the testing of thermonuclear [8] devices. Its islands and reefs were burned by atomic heat, and the waters of its lagoon were contaminated by deposits of radioactive fallout. Thus, for almost a score of years, Bikini, a small outcropping of coral in the mid-Pacific, was identified with the earliest experiments in nuclear explosion. ”

“ All nuclear explosions cause light, heat and blast, which occur immediately. In addition, explosions that are on or close to the ground would create large quantities of dangerous radioactive fallout particles, most of which would fall to earth during the first 24 hours. Explosions high in the air would create smaller radioactive particles, which would not have any real effect on humans until many months or years later, if at all. ”

“ Peal shook his head, but somewhat doubtfully. "On Earth, they're mostly only mesons from strikes by cosmic radiation. Out here, we get only the extremely hard radiation—the shielding of the ship is too thin to affect them. Maybe they might speed up the half-life a little—but they shouldn't make it increase. I've been thinking about them, too. Meteorites show a much greater decay of uranium to lead than the ores on Earth, which might indicate some effect from cosmic radiation. But unless they somehow produce another isotope from uranium that's raising the activity, I can't figure it out. ”

“ The interior of a house or building should be quite safe from any outside source of charged particles emitted by radioactive substances except possibly the most energetic beta rays. Only if the source of charged particles is inside the body so that in spite of their limited ranges the particles can find their way to sensitive tissues, is there any danger. ”

“ These veins are veins of pitchblende which are found hardly anywhere in Europe except in the north of Bohemia and which are worked near the little town of Joachimsthal. And those radioactive bodies are uranium, thorium, helium and chiefly, in the case which we are considering . . ."
"Radium," François interrupted.
"You've said it, my boy: radium. Phenomena of radioactivity occur more or less everywhere; and we may say that they are manifested throughout nature, as in the healing action of thermal springs. But plainly radioactive bodies like radium possess more definite properties. ”

“ Induced Radioactivity.—Radium, thorium, and actinium have the property of acting externally, apart from the Becquerel rays that they emit. They communicate little by little their radioactive properties to substances in their neighborhood, and the latter emit in turn Becquerel rays. The activity can be transmitted to gases, liquids, and solids. The phenomenon is known as induced radioactivity.
Induced radioactivity propagates itself in gases step by step by a sort of conduction, and is not at all due to direct radiation from the body which causes it. ”

“ With the passage of time the linear features would probably
develop; the energetic substratum continually asserting its
influence along such lines of weakness. It is in the highest
degree probable that radioactivity plays no less a part in
Martian history than in terrestrial. The fact of radioactive
heating allows us to assume the thin surface crust and continued
sub-crustal energy throughout the entire period of the planet's
history. ”

“ Teena said.
“I would,” Eddie said. “Everyone is carefully protected. They see to that. Well, anyway, if all of those uranium atoms were shooting radioactive rays around inside of that pile and doing nothing, there would be an awful lot of energy going to waste. So the atomic scientists take certain elements which aren’t radioactive, but can be made radioactive, and shove small pieces of them into holes drilled in the pile.” ”

“ 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. ”