Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles (ionizing radiation). The emission is spontaneous, in that the atom decays without any interaction with another particle from outside the atom (i.e., without a nuclear reaction). Usually, radioactive decay happens due to a process confined to the nucleus of the unstable atom, but, on occasion (as with the different processes of electron capture and internal conversion), an inner electron of the radioactive atom is also necessary to the process.
Radioactive decay is a stochastic (i.e., random) process at the level of single atoms, in that, according to quantum theory, it is impossible to predict when a given atom will decay.[1] However, given a large number of identical atoms (nuclides), the decay rate for the collection is predictable, via the Law of Large Numbers.
The decay, or loss of energy, results when an atom with one type of nucleus, called the parent radionuclide, transforms to an atom with a nucleus in a different state, or a different nucleus, either of which is named the daughter nuclide. Often the parent and daughter are different chemical elements, and in such cases the decay process results in nuclear transmutation. In an example of this, a carbon-14 atom (the "parent") emits radiation (a beta particle, antineutrino, and a gamma ray) and transforms to a nitrogen-14 atom (the "daughter"). By contrast, there exist two types of radioactive decay processes (gamma decay and internal conversion decay) that do not result in transmutation, but only decrease the energy of an excited nucleus. This results in an atom of the same element as before but with a nucleus in a lower energy state. An example is the nuclear isomer technetium-99m decaying, by the emission of a gamma ray, to an atom of technetium-99.
Nuclides produced as daughters are called radiogenic nuclides, whether they themselves are stable or not. A number of naturally occurring radionuclides are short-lived radiogenic nuclides that are the daughters of radioactive primordial nuclides (types of radioactive atoms that have been present since the beginning of the Earth and solar system). Other naturally occurring radioactive nuclides are cosmogenic nuclides, formed by cosmic ray bombardment of material in the Earth's atmosphere or crust. For a summary table showing the number of stable nuclides and of radioactive nuclides in each category, see Radionuclide.
The SI unit of activity is the becquerel (Bq). One Bq is defined as one transformation (or decay) per second. Since any reasonably-sized sample of radioactive material contains many atoms, a Bq is a tiny measure of activity; amounts on the order of GBq (gigabecquerel, 1 x 109 decays per second) or TBq (terabecquerel, 1 x 1012 decays per second) are commonly used. Another unit of radioactivity is the curie, Ci, which was originally defined as the amount of radium emanation (radon-222) in equilibrium with one gram of pure radium, isotope Ra-226. At present it is equal, by definition, to the activity of any radionuclide decaying with a disintegration rate of 3.7 × 1010 Bq. The use of Ci is presently discouraged by the SI.
Explanation
How does it affect the radiation from the nuclear plants to the human beings?
In the case of a nuclear reactor as that of Fukushima, the source or origin of the dangerous radiation ionizante is the material located in the center of the reactor. That material calls himself Uranium-235, which is the only element in the nature that is able to suffer spontaneous fission. Without spirit of confusing, fission means that the element uranium this spontaneous one and constantly “demeaning” in elements chemical smaller called isotopes. These isotopes call themselves radioactive isotopes because they are elements that you/they say goodbye to a lot of radiation ionizante.
And to understand the problem for the one that this passing the reactor of Fukushima, I tell him that the spontaneous fission of the Uranium-235 it generates an enormous quantity of heat (around 1.000 centigrade grades), heat that is used to produce vapor of water that the turbines that generate electricity moves.
Those incredibly hot bars of Uranium-235 they are stored in an enormous steel capsule that has walls of 15 centimeters of grosor. That capsule has to be constantly cooled so that the heating for the fission of the Uranium doesn't arrive to the 2.400 centigrade grades and finish “fusing” not alone the steel capsule but also all the materials surrounding and finish exploding like an atomic minibomba, throwing enormous quantities from radioactive material to the environment. The cooling of the capsule is made making circulate seawater around the capsule, it dilutes that he/she brings himself from the ocean using enormous bombs and pipes.
The tsunami destroyed the bombs that brought seawater for the cooling of the capsule, the fission of the Uranium it has continued unstoppable, the temperature has gone in increase and it has already arrived to 1.200 centigrade grades. That has already originated two explosions and some hot vapors with radioactive isotopes they have left to the environment and they have contaminated 22 people. To avoid the sobrecalentamiento, and in a desperation act, the Japanese authorities have tossed seawater directly to the interior of the capsule and they say that the matter low control, but the threat of an is “foundry” total of the Uranium-235 and the subsequent great explosion of the capsule persists.
This is a good graph of the nuclear plant, this other infografía he/she explains that happened.
PROBLEMS ON THE HEALTH AND THE ENVIRONMENT
Just as we have described it, the problems of health for the radiation of the nuclear plant of Fukushima have several levels, some are already taking place and others will depend of if he/she takes place or not the accident or nuclear explosion.
For the workers that are working in the cooling of the capsule, and they are therefore very near the Uranium and their isotopes, the danger but imminent it is the extreme heat and the possibility from a sharp exhibition to enormous quantities of radiation. They could die burnt instantly or in some hours or days for what calls you the syndrome of sharp exhibition to the radiation. In this syndrome, there is serious damage to the skin, to the digestive system and the bone marrow, the factory of the blood.
The trefoil symbol is used to indicate radioactive material.
The neutrons and protons that constitute nuclei, as well as other particles that approach close enough to them, are governed by several interactions. The strong nuclear force, not observed at the familiar macroscopic scale, is the most powerful force over subatomic distances. The electrostatic force is almost always significant, and, in the case of beta decay, the weak nuclear force is also involved.
The interplay of these forces produces a number of different phenomena in which energy may be released by rearrangement of particles in the nucleus or the change of one particle into others. The rearrangement is hindered energetically, so that it does not occur immediately. Random quantum vacuum fluctuations are theorized to promote relaxation to a lower energy state (the "decay") in a phenomenon known as quantum tunneling.
One might draw an analogy with a snowfield on a mountain: While friction between the ice crystals may be supporting the snow's weight, the system is inherently unstable with regard to a state of lower potential energy. A disturbance would thus facilitate the path to a state of greater entropy: The system will move towards the ground state, producing heat, and the total energy will be distributable over a larger number of quantum states. Thus, an avalanche results. The total energy does not change in this process, but, because of the law of entropy, avalanches happen only in one direction and that is toward the "ground state" — the state with the largest number of ways in which the available energy could be distributed.
Such a collapse (a decay event) requires a specific activation energy. For a snow avalanche, this energy comes as a disturbance from outside the system, although such disturbances can be arbitrarily small. In the case of an excited atomic nucleus, the arbitrarily small disturbance comes from quantum vacuum fluctuations. A radioactive nucleus (or any excited system in quantum mechanics) is unstable, and can, thus, spontaneously stabilize to a less-excited system. The resulting transformation alters the structure of the nucleus and results in the emission of either a photon or a high-velocity particle that has mass (such as an electron, alpha particle, or other type).
Discovery
Radioactivity was first discovered in 1896 by the French scientist Henri Becquerel, while working on phosphorescent materials. These materials glow in the dark after exposure to light, and he suspected that the glow produced in cathode ray tubes by X-rays might be connected with phosphorescence. He wrapped a photographic plate in black paper and placed various phosphorescent salts on it. All results were negative until he used uranium salts. The result with these compounds was a deep blackening of the plate. These radiations were called Becquerel Rays.
It soon became clear that the blackening of the plate had nothing to do with phosphorescence, because the plate blackened when the mineral was in the dark. Non-phosphorescent salts of uranium and metallic uranium also blackened the plate. It was clear that there is a form of radiation that could pass through paper that was causing the plate to become black.
At first it seemed that the new radiation was similar to the then recently-discovered X-rays. Further research by Becquerel, Ernest Rutherford, Paul Villard, Marie Curie, Pierre Curie, and others discovered that this form of radioactivity was significantly more complicated. Different types of decay can occur, producing very different types of radiation. Rutherford was the first to realize that they all occur with the same mathematical exponential formula (see below), and to realize that many decay processes resulted in the transmutation of one element to another.
The early researchers also discovered that many other chemical elements besides uranium have radioactive isotopes. A systematic search for the total radioactivity in uranium ores also guided Marie Curie to isolate a new element polonium and to separate a new element radium from barium. The two elements' chemical similarity would otherwise have made them difficult to distinguish.
Danger of radioactive substances
Alpha particles may be completely stopped by a sheet of paper, beta particles by aluminum shielding. Gamma rays can only be reduced by much more substantial barriers, such as a very thick layer of lead.
Different types of decay of a radionuclide. Vertical: atomic number Z, Horizontal: neutron number N
The dangers of radioactivity and radiation were not immediately recognized. Acute effects of radiation were first observed in the use of X-rays when electrical engineer and physicist Nikola Tesla intentionally subjected his fingers to X-rays in 1896.[2] He published his observations concerning the burns that developed, though he attributed them to ozone rather than to X-rays. His injuries healed later.
The genetic effects of radiation, including the effects on cancer risk, were recognized much later. In 1927, Hermann Joseph Muller published research showing genetic effects, and in 1946 was awarded the Nobel prize for his findings.
Before the biological effects of radiation were known, many physicians and corporations had begun marketing radioactive substances as patent medicine, glow-in-the-dark pigments, and radioactive quackery. Examples were radium enema treatments, and radium-containing waters to be drunk as tonics. Marie Curie spoke out against this sort of treatment, warning that the effects of radiation on the human body were not well understood (Curie later died from aplastic anemia, which was likely caused by exposure to ionizing radiation). By the 1930s, after a number of cases of bone necrosis and death in enthusiasts, radium-containing medical products had nearly vanished from the market.
Types of decay
As for types of radioactive radiation, it was found that an electric or magnetic field could split such emissions into three types of beams. For lack of better terms, the rays were given the alphabetic names alpha, beta, and gamma, still in use today. While alpha decay was seen only in heavier elements (atomic number 52, tellurium, and greater), the other two types of decay were seen in all of the elements.
In analyzing the nature of the decay products, it was obvious from the direction of electromagnetic forces produced upon the radiations by external magnetic and electric fields that alpha rays carried a positive charge, beta rays carried a negative charge, and gamma rays were neutral. From the magnitude of deflection, it was clear that alpha particles were much more massive than beta particles. Passing alpha particles through a very thin glass window and trapping them in a discharge tube allowed researchers to study the emission spectrum of the resulting gas, and ultimately prove that alpha particles are helium nuclei. Other experiments showed the similarity between classical beta radiation and cathode rays: They are both streams of electrons. Likewise gamma radiation and X-rays were found to be similar high-energy electromagnetic radiation.
The relationship between types of decays also began to be examined: For example, gamma decay was almost always found associated with other types of decay, occurring at about the same time, or afterward. Gamma decay as a separate phenomenon (with its own half-life, now termed isomeric transition), was found in natural radioactivity to be a result of the gamma decay of excited metastable nuclear isomers, in turn created from other types of decay.
Although alpha, beta, and gamma were found most commonly, other types of decay were eventually discovered. Shortly after the discovery of the positron in cosmic ray products, it was realized that the same process that operates in classical beta decay can also produce positrons (positron emission). In an analogous process, instead of emitting positrons and neutrinos, some proton-rich nuclides were found to capture their own atomic electrons (electron capture), and emit only a neutrino (and usually also a gamma ray). Each of these types of decay involves the capture or emission of nuclear electrons or positrons, and acts to move a nucleus toward the ratio of neutrons to protons that has the least energy for a given total number of nucleons (neutrons plus protons).
Shortly after discovery of the neutron in 1932, it was discovered by Enrico Fermi that certain rare decay reactions yield neutrons as a decay particle (neutron emission). Isolated proton emission was eventually observed in some elements. It was also found that some heavy elements may undergo spontaneous fission into products that vary in composition. In a phenomenon called cluster decay, specific combinations of neutrons and protons (atomic nuclei) other than alpha particles (helium nuclei) were found to be spontaneously emitted from atoms, on occasion.
Other types of radioactive decay that emit previously seen particles were found, but by different mechanisms. An example is internal conversion, which results in electron and sometimes high-energy photon emission, even though it involves neither beta nor gamma decay. This type of decay (like isomeric transition gamma decay) did not transmute one element to another.
Rare events that involve a combination of two beta-decay type events happening simultaneously (see below) are known. Any decay process that does not violate conservation of energy or momentum laws (and perhaps other particle conservation laws) is permitted to happen, although not all have been detected. An interesting example (discussed in a final section) is bound state beta decay of rhenium-187. In this process, an inverse of electron capture, beta electron-decay of the parent nuclide is not accompanied by beta electron emission, because the beta particle has been captured into the K-shell of the emitting atom. An antineutrino, however, is emitted.
Occurrence and applications
According to the Big Bang theory, stable isotopes of the lightest five elements (H, He, and traces of Li, Be, and B) were produced very shortly after the emergence of the universe, in a process called Big Bang nucleosynthesis. These lightest stable nuclides (including deuterium) survive to today, but any radioactive isotopes of the light elements produced in the Big Bang (such as tritium) have long since decayed. Isotopes of elements heavier than boron were not produced at all in the Big Bang, and these first five elements do not have any long-lived radioisotopes. Thus, all radioactive nuclei are, therefore, relatively young with respect to the birth of the universe, having formed later in various other types of nucleosynthesis in stars (in particular, supernovae), and also during ongoing interactions between stable isotopes and energetic particles. For example, carbon-14, a radioactive nuclide with a half-life of only 5730 years, is constantly produced in Earth's upper atmosphere due to interactions between cosmic rays and nitrogen.
Radioactive decay has been put to use in the technique of radioisotopic labeling, which is used to track the passage of a chemical substance through a complex system (such as a living organism). A sample of the substance is synthesized with a high concentration of unstable atoms. The presence of the substance in one or another part of the system is determined by detecting the locations of decay events.
On the premise that radioactive decay is truly random (rather than merely chaotic), it has been used in hardware random-number generators. Because the process is not thought to vary significantly in mechanism over time, it is also a valuable tool in estimating the absolute ages of certain materials. For geological materials, the radioisotopes and some of their decay products become trapped when a rock solidifies, and can then later be used (subject to many well-known qualifications) to estimate the date of the solidification. These include checking the results of several simultaneous processes and their products against each other, within the same sample. In a similar fashion, and also subject to qualification, the rate of formation of carbon-14 in various eras, the date of formation of organic matter within a certain period related to the isotope's half-life may be estimated, because the carbon-14 becomes trapped when the organic matter grows and incorporates the new carbon-14 from the air. Thereafter, the amount of carbon-14 in organic matter decreases according to decay processes that may also be independently cross-checked by other means (such as checking the carbon-14 in individual tree rings, for example).
Classes and components of the radiation
Classes of radiation ionizante and how to stop it.
The particles alpha (nuclei of helium) they stop when interposing a paper leaf. The particles beta (electrons and positrones) they cannot cross an aluminum layer. However, the rays gamma (photons of high energy) they need a much thicker barrier, and the energy can cross the lead.
He/she was proven that the radiation can be of three different classes, well-known as particles, disintegrations and radiation:
Particle alpha: They are flows of positively compound loaded particles for two neutrons and two protons (nuclei of helium). they are deviated by electric and magnetic fields. They are not very penetrating, although very ionizantes. They are very energy. They were discovered by Rutherford who made pass particles alpha through a fine glass and it caught them in a discharge tube. This radiation type emits it nuclei of heavy elements located at the end of the periodic chart (AT >100). These nuclei have many protons and the electric repulsion is very strong, for what you/they spread to obtain N approximately similar to Z, and for it is emitted it a particle alpha. In the process he/she comes off a lot of energy that becomes the kinetic energy of the particle alpha, for what these particles go out with very high speeds.
Disintegration beta: They are flows of electrons (beta negatives) or positrones (positive beta) resultants of the disintegration of the neutrons or protons of the nucleus when this is in an excited state. It is deviated by magnetic fields. It is more penetrating, although their ionization power is not as high as that of the particles alpha. Therefore, when an atom expels a particle beta, its atomic number it increases or it diminishes an unit (due to the won proton or lost). three types of radiation beta Exist: the radiation beta - that consists in the spontaneous emission of electrons on the part of the nuclei; the radiation beta+, in which a proton of the nucleus disintegrates and he/she gives place to a neutron, to a positrón or particle Beta+ and a neutrino, and lastly the electronic capture that one gives in nuclei with excess of protons, in which the nucleus captures an electron of the electronic bark that will unite to a proton of the nucleus to give a neutron.
Radiation gamma: It is electromagnetic waves. It is the most penetrating type in radiation. To the being electromagnetic waves of longitude of short wave, they have bigger penetration and very thick layers of lead or concrete are needed to stop them. In this radiation type the nucleus doesn't lose its identity, but rather he/she comes off of the energy that he has more than enough to pass to another state of lower energy emitting the rays gamma, that is to say very energy photons. This emission type accompanies to the radiations alpha and beta. To be so penetrating and so energy, this is the most dangerous type in radiation.
The laws of radioactive disintegration, described by Frederick Soddy and Kasimir Fajans, are:
When a radioactive atom emits a particle alpha, the mass of the atom (TO) resultant diminishes in 4 units and the atomic number (Z) in 2.
When a radioactive atom emits a particle beta, the atomic number (Z) it increases or it diminishes in an unit and the atomic mass (TO) he/she stays constant.
When an excited nucleus emits radiation gamma, it doesn't vary neither its mass neither its atomic number: does it only lose a quantity of energy h? (where "h" is the constant of Planck and "? " it is the frequency of the emitted radiation).
The first two laws indicate that, when an atom emits a radiation alpha or beta, he/she becomes another atom of a different element. This new element can be radioactive and to transform in other, and so forth, with what the calls radioactive series are generated.
[editar]Causa of the radioactivity
In general they are radioactive the substances that don't present a correct balance between protons or neutrons, just as sample the graph to the beginning of the article. When the number of neutrons is excessive or too small regarding the number of protons, it becomes more difficult than the due strong nuclear force to the effect of the piones exchange it can maintain them united. Possibly, the imbalance is corrected by means of the liberation of the excess of neutrons or protons, in form of particles to that are really nuclei of helium, and particles ß that can be electrons or positrones. These emissions take to two radioactivity types, already mentioned:
Radiation to that unloads the atomic nuclei in 4 units másicas, and it changes the atomic number in two units.
Radiation ß that doesn't change the mass of the nucleus, since implies the conversion of a proton in a neutron or vice versa, and it changes the atomic number in a single unit (positive or negative, according to if the emitted particle is an electron or a positrón).
The radiation, on the other hand, is due to that the nucleus passes from an excited state of more energy to another of smaller energy that can continue being unstable and to give place to the emission of more type radiation to, ß or?. The radiation? it is, therefore, a type of very penetrating electromagnetic radiation, since has a high energy for emitted photon.
