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Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. This decay, or loss of energy, results in an atom of one type, called the parent nuclide transforming to an atom of a different type, called the daughter nuclide. For example: a carbon-14 atom (the "parent") emits radiation and transforms to a nitrogen-14 atom (the "daughter.") This is a random process on the atomic level, in that it is impossible to predict when a particular atom will decay, but given a large number of similar atoms, the decay rate, on average, is predictable. The nucleus of an atom is the very small dense region, of positive charge, in its centre consisting of nucleons (protons and neutrons). ... Radiation as used in physics, is energy in the form of waves or moving subatomic particles. ... Particle radiation is the radiation of energy by means of small fast-moving particles that have energy and mass. ... Legend Î³ = Gamma rays HX = Hard X-rays SX = Soft X-Rays EUV = Extreme ultraviolet NUV = Near ultraviolet Visible light NIR = Near infrared MIR = Moderate infrared FIR = Far infrared Radio waves EHF = Extremely high frequency (Microwaves) SHF = Super high frequency (Microwaves) UHF = Ultra high frequency VHF = Very high frequency HF = High... Random redirects here. ...

The trefoil symbol is used to indicate radioactive material.

## Explanation

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 is the weak nuclear force. This article or section does not adequately cite its references or sources. ... In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... A Feynman diagram of a strong proton-neutron interaction mediated by a neutral pion. ... Macroscopic is commonly used to describe physical objects that are measurable and observable by the naked eye. ... Coulombs torsion balance In physics, Coulombs law is an inverse-square law indicating the magnitude and direction of electrostatic force that one stationary, electrically charged object of small dimensions (ideally, a point source) exerts on another. ... The weak interaction (often called the weak force or sometimes the weak nuclear force) is one of the four fundamental interactions of nature. ...

The interplay of these forces is simple. 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 (with the extra energy moving elsewhere). One might draw an analogy with a snowfield on a mountain: while friction between the snow crystals can support the snow's weight, the system is inherently unstable with regards to a lower-potential-energy state, and a disturbance may facilitate the path to a greater entropy state (i.e., towards the ground state where heat will be produced, and thus total energy is distributed over a larger number of quantum states). Thus, an avalanche results. The total energy does not change in this process, but because of entropy effects, avalanches only happen in one direction, and the end of this direction, which is dictated by the largest number of chance-mediated ways to distribute available energy, is what we commonly refer to as the "ground state." Friction is the force that opposes the relative motion or tendency toward such motion of two surfaces in contact. ... A Himalayan avalanche near Mount Everest. ...

Such a collapse (a decay event) requires a specific activation energy. In the case of a snow avalanche, this energy classically 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 nucleus (or any excited system in quantum mechanics) is unstable, and can thus spontaneously stabilize to a less-excited system. This process is driven by entropy considerations: the energy does not change, but at the end of the process, the total energy is more diffused in spacial volume. The resulting transformation alters the structure of the nucleus. Such a reaction is thus a nuclear reaction, in contrast to chemical reactions, which also are driven by entropy, but which involve changes in the arrangement of the outer electrons of atoms, rather than their nuclei. The sparks generated by striking steel against a flint provide the activation energy to initiate combustion in this Bunsen burner. ... The nucleus of an atom is the very small dense region, of positive charge, in its centre consisting of nucleons (protons and neutrons). ... In the description of the interaction between elementary particles in quantum field theory, a virtual particle is a temporary elementary particle, used to describe an intermediate stage in the interaction. ... In nuclear physics, a nuclear reaction is a process in which two nuclei or nuclear particles collide to produce products different from the initial particles. ... Vapours of hydrogen chloride in a beaker and ammonia in a test tube meet to form a cloud of a new substance, ammonium chloride A chemical reaction is a process that results in the interconversion of chemical substances. ... e- redirects here. ...

Some nuclear reactions do involve external sources of energy, in the form of collisions with outside particles. However, these are not considered decay. Rather, they are examples of induced nuclear reactions. Nuclear fission and fusion are common types of induced nuclear reactions. In nuclear physics, a nuclear reaction is a process in which two nuclei or nuclear particles collide to produce products different from the initial particles. ... In nuclear physics, a nuclear reaction is a process in which two nuclei or nuclear particles collide to produce products different from the initial particles. ... For the generation of electrical power by fission, see Nuclear power plant An induced nuclear fission event. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ...

## 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 thought that the glow produced in cathode ray tubes by X-rays might somehow be connected with phosphorescence. So he tried wrapping a photographic plate in black paper and placing various phosphorescent minerals on it. All results were negative until he tried using uranium salts. The result with these compounds was a deep blackening of the plate. Antoine Henri Becquerel (December 15, 1852 â€“ August 25, 1908) was a French physicist, Nobel laureate, and one of the discoverers of radioactivity. ... Phosphorescent powder under visible light, ultraviolet light, and total darkness. ... Cathode ray tube employing electromagnetic focus and deflection Cutaway rendering of a color CRT Electron guns Electron beams Focusing coils Deflection coils Anode connection Mask for separating beams for red, green, and blue part of displayed image Phosphor layer with red, green, and blue zones Close-up of the phosphor... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition, a highly ordered atomic structure and specific physical properties. ... General Name, Symbol, Number uranium, U, 92 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery gray metallic; corrodes to a spalling black oxide coat in air Standard atomic weight 238. ...

However, it soon became clear that the blackening of the plate had nothing to do with phosphorescence because the plate blackened when the mineral was kept in the dark. Also non-phosphorescent salts of uranium and even metallic uranium blackened the plate. Clearly there was some new form of radiation that could pass through paper that was causing the plate to blacken.

Alpha particles may be completely stopped by a sheet of paper, beta particles by aluminum shielding. Gamma rays, however, can only be reduced by much more substantial obstacles, such as a very thick piece of lead.

At first it seemed that the new radiation was similar to the then recently discovered X-rays. However further research by Becquerel, Marie Curie, Pierre Curie, Ernest Rutherford and others discovered that radioactivity was significantly more complicated. Different types of decay can occur, but Rutherford was the first to realize that they all occur with the same mathematical approximately exponential formula (see below). Image File history File links Alfa_beta_gamma_radiation. ... Image File history File links Alfa_beta_gamma_radiation. ... Madame Curie redirects here. ... // Pierre Curie (Paris, France, May 15, 1859 â€“ April 19, 1906, Paris) was a French physicist, a pioneer in crystallography, magnetism, piezoelectricity and radioactivity. ... Ernest Rutherford, 1st Baron Rutherford of Nelson OM PC FRS (30 August 1871 - 19 October 1937), widely referred to as Lord Rutherford, was a nuclear physicist who became known as the father of nuclear physics. ...

Although alpha, beta, and gamma are most common, other types of decay were eventually discovered. Shortly after discovery of the neutron in 1932, it was discovered by Enrico Fermi that certain rare decay reactions give rise to neutrons as a decay particle. Isolated proton emission was also eventually observed in some elements. 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), analogously to negative electrons. Each of the two types of beta decay acts to move a nucleus toward a ratio of neutrons and protons which has the least energy for the combination. Finally, in a phenomenon called cluster decay, specific combinations of neutrons and protons other than alpha particles were found to occasionally spontaneously be emitted from atoms. This article or section does not adequately cite its references or sources. ... Enrico Fermi (September 29, 1901 â€“ November 28, 1954) was an Italian physicist most noted for his work on the development of the first nuclear reactor, and for his contributions to the development of quantum theory, particle physics and statistical mechanics. ... Proton emission (also known as proton radioactivity) is a type of radioactive decay in which a proton is ejected from a nucleus. ... The first detection of the positron in 1932 by Carl D. Anderson The positron is the antiparticle or the antimatter counterpart of the electron. ... 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. ... Positron emission is a type of beta decay, sometimes referred to as beta plus (Î²+). 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. ... Cluster decay is the nuclear process in which a radioactive atom emits a cluster of neutrons and protons. ...

Still other types of radioactive decay were found which emit previously seen particles, 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. . Internal conversion is a radioactive decay process where an excited nucleus interacts with an electron in one of the lower electron shells, causing the electron to be emitted from the atom. ...

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. watecs ... A radionuclide is an atom with an unstable nucleus, which is a nucleus characterized of excess energy which is available to be imparted either to a newly-created radiation particle within the nucleus, or else to an atomic electron (see internal conversion) . The radionuclide, in this process, undergoes radioactive decay... General Name, Symbol, Number polonium, Po, 84 Chemical series metalloids Group, Period, Block 16, 6, p Appearance silvery Standard atomic weight (209) gÂ·molâˆ’1 Electron configuration [Xe] 4f14 5d10 6s2 6p4 Electrons per shell 2, 8, 18, 32, 18, 6 Physical properties Phase solid Density (near r. ... General Name, Symbol, Number radium, Ra, 88 Chemical series alkaline earth metals Group, Period, Block 2, 7, s Appearance silvery white metallic Standard atomic weight (226) gÂ·molâˆ’1 Electron configuration [Rn] 7s2 Electrons per shell 2, 8, 18, 32, 18, 8, 2 Physical properties Phase solid Density (near r. ... General Name, Symbol, Number barium2, Ba, 56 Chemical series alkaline earth metals Group, Period, Block 2, 6, s Appearance silvery white Standard atomic weight 137. ...

The dangers of radioactivity and of radiation were not immediately recognized. Acute effects of radiation were first observed in the use of X-rays when the Serbo-Croatian-American electric engineer Nikola Tesla intentionally subjected his fingers to X-rays in 1896. He published his observations concerning the burns that developed, though he attributed them to ozone rather than to the X-rays. Fortunately his injuries healed later. Nikola Tesla (1856-1943)[1] was a world-renowned Serbian inventor, physicist, mechanical engineer and electrical engineer. ...

The genetic effects of radiation, including the effects on cancer risk, were recognized much later. It was only in 1927 that Hermann Joseph Muller published his research that showed the genetic effects. In 1947 he was awarded the Nobel prize for his findings. Hermann Joseph H. J. Muller (December 21, 1890 â€“ April 5, 1967) was a Nobel Prize-winning American geneticist and educator, best known for his work on the physiological and genetic effects of radiation (X-ray mutagenesis) as well as his outspoken political beliefs. ... Nobel Prize medal. ...

## Modes of decay

Radionuclides can undergo a number of different reactions. These are summarized in the following table. A nucleus with positive charge (atomic number) Z and atomic weight A is represented as (A, Z).

Mode of decay Participating particles Daughter nucleus
Decays with emission of nucleons:
Alpha decay An alpha particle (A=4, Z=2) emitted from nucleus (A-4, Z-2)
Proton emission A proton ejected from nucleus (A-1, Z-1)
Neutron emission A neutron ejected from nucleus (A-1, Z)
Double proton emission Two protons ejected from nucleus simultaneously (A-2, Z-2)
Spontaneous fission Nucleus disintegrates into two or more smaller nuclei and other particles -
Cluster decay Nucleus emits a specific type of smaller nucleus (A1, Z1) larger than an alpha particle (A-A1, Z-Z1) + (A1,Z1)
Different modes of beta decay:
Beta-Negative decay A nucleus emits an electron and an antineutrino (A, Z+1)
Positron emission, also Beta-Positive decay A nucleus emits a positron and a neutrino (A, Z-1)
Electron capture A nucleus captures an orbiting electron and emits a neutrino - The daughter nucleus is left in an excited and unstable state (A, Z-1)
Double beta decay A nucleus emits two electrons and two antineutrinos (A, Z+2)
Double electron capture A nucleus absorbs two orbital electrons and emits two neutrinos - The daughter nucleus is left in an excited and unstable state (A, Z-2)
Electron capture with positron emission A nucleus absorbs one orbital electron, emits one positron and two neutrinos (A, Z-2)
Double positron emission A nucleus emits two positrons and two neutrinos (A, Z-2)
Transitions between states of the same nucleus:
Gamma decay Excited nucleus releases a high-energy photon (gamma ray) (A, Z)
Internal conversion Excited nucleus transfers energy to an orbital electron and it is ejected from the atom (A, Z)

## Decay chains and multiple modes

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. ...

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

Of the commonly occurring forms of radioactive decay, the only one that changes the number of aggregate protons and neutrons (nucleons) contained in the nucleus 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 two baryons: the neutron and the proton. ... Modular arithmetic (sometimes called modulo arithmetic, or clock arithmetic because of its use in the 24-hour clock system) is a system of arithmetic for integers, where numbers wrap around after they reach a certain value â€” 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 nuclides are so highly unstable that virtually none of them have survived to today. Most radioactive nuclei are therefore relatively young, having formed in stars (particularly supernovae) and 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. According to the Big Bang theory, the universe originated in an infinitely dense and physically paradoxical singularity. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Standard atomic weight 4. ... General Name, Symbol, Number lithium, Li, 3 Chemical series alkali metals Group, Period, Block 1, 2, s Appearance silvery white/grey Standard atomic weight 6. ... STAR is an acronym for: Organizations Society of Ticket Agents and Retailers], the self-regulatory body for the entertainment ticket industry in the UK. Society for Telescopy, Astronomy, and Radio, a non-profit New Jersey astronomy club. ... Multiwavelength X-ray image of the remnant of Keplers Supernova, SN 1604. ... Carbon-14 is the radioactive isotope of carbon discovered February 27, 1940, by Martin Kamen and Sam Ruben. ...

Radioactive decay has been put to use in the technique of radioisotopic labeling, 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 labeling is a technique for tracking the passage of a sample of substance through a system. ... This article does not cite any references or sources. ...

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 certain 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. Random redirects here. ... A plot of the Lorenz attractor for values r = 28, Ïƒ = 10, b = 8/3 In mathematics and physics, chaos theory describes the behavior of certain nonlinear dynamical systems that under specific conditions exhibit dynamics that are sensitive to initial conditions (popularly referred to as the butterfly effect). ... In computing, a hardware random number generator is an apparatus that generates random numbers from a physical process. ...

The decay rate, or activity, of a radioactive substance are characterized by:

Constant quantities:

• half life - symbol t1 / 2 - the time for half of a substance to decay.
• mean lifetime - symbol τ - the average lifetime of any given particle.
• decay constant - symbol λ - the inverse of the mean lifetime.
(Note that although these are constants, they are associated with statistically random behavior of substances, and predictions using these constants are less accurate for small number of atoms.)

Time-variable quantities: The half-life of a quantity, subject to exponential decay, is the time required for the quantity to decay to half of its initial value. ... 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. ... A quantity is said to be subject to exponential decay if it decreases at a rate proportional to its value. ...

• Total activity - symbol A - number of decays an object undergoes per second.
• Number of particles - symbol N - the total number of particles in the sample.
• Specific activity - symbol SA - number of decays per second per amount of substance. The "amount of substance" can be the unit of either mass or volume.)

These are related as follows:

$t_{1/2} = frac{ln(2)}{lambda} = tau ln(2)$
$A = - frac{dN}{dt} = lambda N$
$S_A a_0 = - frac{dN}{dt}bigg|_{t=0} = lambda N_0$
where
$a_0$ is the initial amount of active substance - substance that has the same percentage of unstable particles as when the substance was formed.

### Activity measurements

The units in which activities are measured are: becquerel (symbol Bq) = number of disintegrations per second; curie (Ci) = 3.7 × 1010 disintegrations per second. Low activities are also measured in disintegrations per minute (dpm). 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. ... The curie (symbol Ci) is a former unit of radioactivity, defined as 3. ...

## Decay timing

As discussed above, the decay of an unstable nucleus 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 –dN 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, then the probability of decay (– dN/N) is proportional to dt: A quantity is said to be subject to exponential decay if it decreases at a rate proportional to its value. ...

$left(-frac{dN}{N} right) = lambda cdot dt$

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 first-order differential equation is the following function: Look up Î›, Î» in Wiktionary, the free dictionary. ... A simulation of airflow into a duct using the Navier-Stokes equations A differential equation is a mathematical equation for an unknown function of one or several variables which relates the values of the function itself and of its derivatives of various orders. ... 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 non-negative 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. ... The exponential function is one of the most important functions in mathematics. ... In mathematics, a continuous function is a function for which, intuitively, small changes in the input result in 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 (or simply the mean) of a list of numbers is the sum of all the members of the list divided by the number of items in the list. ...

$tau = frac{1}{lambda}$

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. ...

## References

• "Radioactivity", Encyclopædia Britannica. 2006. Encyclopædia Britannica Online. 18 Dec. 2006

Results from FactBites:

 Radioactive decay - Wikipedia, the free encyclopedia (1973 words) Radioactive decay is the set of various processes by which unstable atomic nuclei emit subatomic particles (radiation). 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). On the premise that radioactive decay is truly random (rather than merely chaotic), it has been used in hardware random-number generators and is an invaluable tool in estimating the absolute ages of geological materials and young organic matter.
 NationMaster - Encyclopedia: Radioactive decay (532 words) The SI unit for measuring radioactive decay is the becquerel (Bq). The radioactive half-life for a given radioisotope is a measure of the tendency of the nucleus to "decay" or "disintegrate" and as such is based purely upon that probability. Radioactive decay is a statistical process which depends upon the instability of the particular radioisotope, but which for any given nucleus in a sample is completely unpredictable.
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