Radioactive decay is the set of various processes by which unstable atomic nuclei (nuclides) emit subatomic particles (radiation). Decay is said to occur in the parent nucleus and produces a daughter nucleus. This is a random process, i.e. it is impossible to predict the decay of individual atoms. A stylized representation of a lithium atom. ... Isotopes are atoms of a chemical element whose nuclei have the same atomic number, Z, but different atomic weights, A. The word isotope, meaning at the same place, comes from the fact that isotopes are located at the same place on the periodic table. ... A subatomic particle is a particle smaller than an atom: it may be elementary or composite. ... Radiation has a variety of different meanings. ...

The trefoil symbol is used to indicate radioactive material. The Unicode encoding of this symbol is U+2622 (☢).

The SI unit for measuring radioactive decay is the becquerel (Bq). If a quantity of radioactive material produces one decay event per second, it has an activity of one Bq. Since any reasonably-sized sample of radioactive material contains very many atoms, a becquerel is a tiny level of activity; numbers on the order of gigabecquerels are seen more commonly. From http://www. ... From http://www. ... Jump to: navigation, search Unicode is an international standard whose goal is to provide the means by which text of all forms and languages can be encoded for use by computers. ... Jump to: navigation, search The International System of Units (abbreviated SI from the French phrase, Système International dUnités) is the most widely used system of units. ... The becquerel (symbol Bq) is the SI derived unit of radioactivity, defined as the activity of a quantity of radioactive material in which one nucleus decays per second. ...

General introduction

The neutrons and protons that constitute nuclei, as well as other particles that may approach 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 also significant. Of lesser importance are the weak nuclear force and the gravitational force. Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 939. ... Properties In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... The strong nuclear force or strong interaction (also called color force or colour force) is a fundamental force of nature which affects only quarks and antiquarks, and is mediated by gluons in a similar fashion to how the electromagnetic force is mediated by photons. ... Macroscopic means measurable and observable by the naked eye; describes existence as we perceive it. ... In physics, the electrostatic force is the force arising between static (that is, non-moving) electric charges. ... The weak nuclear force or weak interaction is one of the four fundamental forces of nature. ... This article covers the physics of gravitation. ...

The interplay of these forces is very complex. Some configurations of the particles in a nucleus have the property that, should they shift ever so slightly, the particles could fall into a lower-energy arrangement. One might draw an analogy with a tower of sand: while friction between the sand grains can support the tower's weight, a disturbance will unleash the force of gravity and the tower will collapse. Patterns in the sand Sand is an example of a class of materials called granular matter. ... Jump to: navigation, search In physics, friction is the non-conservative resistive force that occurs when two surfaces travel along each other when forced together. ...

Such a collapse (a decay event) requires a certain activation energy. In the case of the tower of sand, this energy must come from outside the system, in the form of a gentle prod or swift kick. In the case of an atomic nucleus, it is already present. Quantum-mechanical particles are never at rest; they are in continuous random motion. Thus, if its constituent particles move in concert, the nucleus can spontaneously destabilize. The resulting transformation changes the structure of the nucleus; thus it is a nuclear reaction, in contrast to chemical reactions, which concern interactions of electrons with nuclei. The activation energy in chemistry is the energy needed by a system to initiate a particular process. ... Jump to: navigation, search Fig. ... In nuclear physics, a nuclear reaction is a process in which two nuclei or nuclear particles collide, to produce products different to the initial products. ... Jump to: navigation, search A chemical reaction is a process involving one, two or more substances (called reactants), characterized by a chemical change and yielding one or more product(s) which are different from the reactants. ... Jump to: navigation, search Properties The electron is a fundamental subatomic particle which carries a negative electric charge. ...

(Some nuclear reactions do involve external sources of energy, in the form of "collisions" with outside particles. However, these are not considered decay. Rather this is induced fission or fusion.) In nuclear physics, a nuclear reaction is a process in which two nuclei or nuclear particles collide, to produce products different to the initial products. ... In general fission is a splitting or breaking up into parts. ... Fusion typically refers to the merging of two or more entities into a single one: In physics, nuclear fusion is the combination of two atomic nuclei into a single nucleus. ...

Decay timing

As discussed above, the decay of an unstable nucleus (radionuclide) is entirely random and it is impossible to predict when a particular atom will decay. However, it is equally likely to decay at any time. Therefore, given a sample of a particular radioisotope, the number of decay events expected to occur in a small interval of time dt is proportional to the number of atoms present. If N is the number of atoms, the following first-order differential equation can be written: Atoms of chemical elements may have many isotopes (different forms) with different atomic numbers and different atomic weights. ... In mathematics, a differential equation is an equation in which the derivatives of a function appear as variables. ...

Particular radionuclides decay at different rates, each having its own decay constant (λ). The negative sign indicates that N decreases with each decay event. The solution to this equation is the following function: Jump to: navigation, search Lambda (upper case Λ, lower case λ) is the 11th letter of the Greek alphabet. ... In mathematics, a function is a relation, such that each element of a set (the domain) is associated with a unique element of another (possibly the same) set (the codomain, not to be confused with the range). ...

This function represents exponential decay. It is only an approximate solution, for two reasons. Firstly, the exponential function is continuous, but the physical quantity N can only take positive integer values. Secondly, because it describes a random process, it is only statistically true. However, in most common cases, N is a very large number and the function is a good approximation. A quantity is said to be subject to exponential decay if it decreases at a rate proportional to its value. ... Jump to: navigation, search The exponential function is one of the most important functions in mathematics. ... In mathematics, a continuous function is a function in which arbitrarily small changes in the input produce arbitrarily small changes in the output. ... Natural number can mean either a positive integer (1, 2, 3, 4, ...) or a non-negative integer (0, 1, 2, 3, 4, ...). Natural numbers have two main purposes: they can be used for counting (there are 3 apples on the table), or they can be used for ordering (this is...

In addition to the decay constant, radioactive decay is sometimes characterized by the mean lifetime. Each atom "lives" for a finite amount of time before it decays, and the mean lifetime is the arithmetic mean of all the atoms' lifetimes. It is represented by the symbol τ, and is related to the decay constant as follows: Given an assembly of elements, the number of which decreases ultimately to zero, the lifetime (also called the mean lifetime) is a certain number that characterizes the rate of reduction (decay) of the assembly. ... In mathematics and statistics, the arithmetic mean of a set of numbers is the sum of all the members of the set divided by the number of items in the set (cardinality). ... Tau (upper case Τ, lower case Ï„) is the 19th letter of the Greek alphabet. ...

A more commonly used parameter is the half-life. Given a sample of a particular radionuclide, the half-life is the time taken for half the radionuclide's atoms to decay. The half life is related to the decay constant as follows: Half-Life For a quantity subject to exponential decay, the half-life is the time required for the quantity to fall to half of its initial value. ...

This relationship between the half-life and the decay constant shows that highly radioactive substances are quickly spent, while those that radiate weakly endure longer. Half-lives of known radionuclides vary widely, from more than 10¹² years for very nearly stable nuclides, to 10^-6 seconds for highly unstable ones. (Redirected from 1 E19 s) To help compare orders of magnitude of different times, this page lists times longer than 1019 seconds (320,000 million years) See also times of other orders of magnitude. ... To help compare orders of magnitude of different times this page lists times between 10-6 seconds and 10-5 seconds (1. ...

Modes of decay

Radionuclides can undergo a number of different reactions. These are summarized in the following table, in rough order of increasing rarity. For brevity, neutrons, protons and electrons are represented by the symbols n, p+, and e- respectively.

Radioactive decay results in a loss of mass, which is converted to energy (the disintegration energy) according to the formula E = mc². This energy is commonly released as photons (gamma radiation). Alpha decay is a form of radioactive decay in which an atomic nucleus ejects an alpha particle and transforms into a nucleus with mass number 4 less and atomic number 2 less. ... In nuclear physics, beta decay (sometimes called neutron decay) is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted. ... Antineutrinos, the antiparticles of neutrinos, are neutral particles produced in nuclear beta decay. ... This article is about electromagnetic radiation. ... For the Science Fiction weapon, as seen in Star Trek, see Photon torpedo. ... This article is about electromagnetic radiation. ... Positron emission is a type of beta decay, sometimes referred to as beta plus (β+). In beta plus decay, a proton is converted to a neutron via the weak nuclear force and a beta plus particle (a positron) and a neutrino are emitted. ... The first detection of the positron in 1932 by Carl D. Anderson The positron is the antiparticle or the antimatter counterpart of the electron. ... The neutrino is an elementary particle. ... This article is about the nuclear process. ... Electron atomic and molecular orbitals In atomic physics, an electron orbital (or simply orbital) is the description of the behavior of an electron in an atom or molecule according to quantum mechanics. ... Proton emission (also known as proton radioactivity) is a type of radioactive decay in which a proton is ejected from a nucleus. ... Neutron emission is a type of radioactive decay in which an atom contains excess neutrons and a neutron is simply ejected from the nucleus. ... Electron capture is a decay mode for chemical elements that will occur when there are too many protons in the nucleus of an atom, and there isnt enough energy to emit a positron; however, it continues to be a viable decay mode for radioactive elements that can decay by... Spontaneous fission (SF) is a form of radioactive decay characteristic of very heavy isotopes, and is theoretically possible for any atomic nucleus whose mass is greater than or equal to 100 amu (elements near ruthenium). ... Cluster decay is the nuclear process in which a radioactive atom emits a cluster of neutrons and protons. ... In the process of beta decay unstable nuclei decay by converting a neutron in the nucleus to a proton and emitting an electron and anti-neutrino. ... Mass is a property of physical objects that, roughly speaking, measures the amount of matter they contain. ... The term mass in special relativity can be used in different ways, occasionally leading to a great deal of confusion. ...

Decay chains and multiple modes

Many radionuclides have several different observed modes of decay. Bismuth-212, for example, has three. General Name, Symbol, Number bismuth, Bi, 83 Chemical series poor metals Group, Period, Block 15, 6, p Appearance lustrous reddish white Atomic mass 208. ...

The daughter nuclide of a decay event is usually also unstable, sometimes even more unstable than the parent. If this is the case, it will proceed to decay again. A sequence of several decay events, producing in the end a stable nuclide, is a decay chain. Nearly all the decay products of radioactive decay are themselves radioactive. ...

Of the commonly occurring forms of radioactive decay, the only one that changes the number of aggregate protons and neutrons (nucleons) contained in the nuclide is alpha emission, which reduces it by four. Thus, the number of nucleons modulo 4 is preserved across any decay chain. In physics a nucleon is a collective name for the two baryons the neutron and the proton. ... Jump to: navigation, search Modular arithmetic is a system of arithmetic for integers, where numbers wrap around after they reach a certain value — the modulus. ...

Occurrence and applications

According to the Big Bang theory, radioactive isotopes of the lightest elements (H, He, and traces of Li) were produced very shortly after the emergence of the universe. However, these structures are so highly unstable that virtually none of these original nuclides remain today. With this exception, all unstable nuclides were formed in stars (particularly supernovae). According to the Big Bang theory, the universe originated in an infinitely dense and physically paradoxical singularity. ... Jump to: navigation, search General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... Jump to: navigation, search General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Atomic mass 4. ... General Name, Symbol, Number lithium, Li, 3 Chemical series alkali metals Group, Period, Block 1, 2, s Appearance silvery white/gray Atomic mass 6. ... Jump to: navigation, search The Pleiades star cluster A star is a massive body of plasma in outer space that is currently producing or has produced energy through nuclear fusion. ... Remnant of Keplers Supernova, SN 1604. ...

Radioactive decay has been put to use in the technique of radioisotopic labelling, 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. Radioisotopic labelling is a technique for tracking the passage of a sample of substance through a system. ... Jump to: navigation, search In biology and ecology, an organism (in Greek organon = instrument) is an assembly of organs that influence each other in such a way that they function as a more or less stable whole and have properties of life. ...

On the premise that radioactive decay is truly random (rather than merely chaotic), it has been used in hardware random-number generators. In ordinary language, the word random is used to express apparent lack of purpose or cause. ... Jump to: navigation, search In mathematics and physics, chaos theory deals with the behavior of certain nonlinear dynamical systems that (under certain conditions) exhibit the phenomenon known as chaos, most famously characterised by sensitivity to initial conditions (see butterfly effect). ... In computing, a hardware random number generator is an apparatus that generates random numbers from a physical process. ...

Related topics

• Nuclear physics
• Poisson process
• Radiation
• Radioactive contamination
• Radiometric dating

Nuclear physics is the branch of physics concerned with the nucleus of the atom. ... It has been suggested that compound Poisson process be merged into this article or section. ... Radiation has a variety of different meanings. ... The radiation warning symbol (trefoil). ... Jump to: navigation, search Radiometric dating is a technique used to date materials based on a knowledge of the decay rates of naturally occurring isotopes, and the current abundances. ...

External links

• Decay chains
• Uranium-238 decay chain
• Sulfur-38 decay chain
• List of decay modes
• Uranium-232 decay chain, Bismuth-212 decay modes
• Nomenclature of Radiochemistry
• Radiochemistry Primer
• Nuclear stability
• A page explaining nuclear decay
• Table of Nuclides