Radioactive decay also known as nuclear decayradioactivity or nuclear radiation is the process by which an unstable atomic nucleus loses energy in terms of mass in its rest frame by emitting radiationsuch as an alpha particlebeta particle with neutrino or only a neutrino in the case of electron captureor a gamma ray or electron in the case of internal conversion.
A material containing such unstable nuclei is considered radioactive. Certain highly excited short-lived nuclear states can decay through neutron emissionor more rarely, proton emission.
Radioactive decay is a stochastic i. According to quantum theoryit is impossible to predict when a particular atom will decay,    regardless of how long the atom has existed.
However, for a collection of atoms, the collection's expected decay rate is characterized in terms of their measured decay constants or half-lives. This is the basis of radiometric dating. The half-lives of radioactive atoms have no known upper limit, spanning a time range of over 55 orders of magnitudefrom nearly instantaneous to far longer than the age of the universe. A radioactive nucleus with zero spin can have no defined orientation, and hence emits the total momentum of its decay products isotropically all directions and without bias.
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If there are multiple particles produced during a single decay, as in beta decaytheir relative angular distribution, or spin directions may not be isotropic. Decay products from a nucleus with spin may be distributed non-isotropically with respect to that spin direction, either because of an external influence such as an electromagnetic fieldor because the nucleus was produced in a dynamic process that constrained the direction of its spin. Such a parent process could be a previous decay, or a nuclear reaction.
The decaying nucleus is called the parent radionuclide or parent radioisotope [note 2]and the process produces at least one daughter nuclide. Except What is the process of radiometric hookup gamma decay or internal conversion from a nuclear excited statethe decay is a nuclear transmutation resulting in a daughter containing a different number of protons or neutrons or both. When the number of protons changes, an atom of a different chemical element is created.
The first decay processes to be discovered were alpha decay, beta decay, and gamma decay. Alpha decay occurs when the nucleus ejects an alpha particle helium nucleus. This is the most common process of emitting nucleonsbut highly excited nuclei can eject single nucleons, or in the case of cluster decayspecific light nuclei of other elements.
Beta decay occurs in two ways: Highly excited neutron-rich nuclei, formed as the product of other types of decay, occasionally What is the process of radiometric hookup energy by way of neutron emission, resulting in a change from one isotope to another of the same element. The nucleus may capture an orbiting electron, causing a proton to convert into a neutron in a process called electron capture. All of these processes result in a well-defined nuclear transmutation.
By contrast, there are radioactive decay processes that do not result in a nuclear transmutation. The energy of an excited nucleus may be emitted as a gamma ray in a process called gamma decayor that energy may be lost when the nucleus interacts with an orbital electron causing its ejection from the atom, in a process called internal conversion. Another type of radioactive decay results in products that vary, appearing as two or more "fragments" of the original nucleus with a range of possible masses.
This decay, called spontaneous fissionhappens when a large unstable nucleus spontaneously splits into two or occasionally three smaller daughter nuclei, and generally leads to the emission of gamma rays, neutrons, or other particles from those products.
For a summary table showing the number of stable and radioactive nuclides in each category, see radionuclide. There are 28 naturally occurring chemical elements on Earth that are radioactive, consisting of 33 radionuclides 5 elements have 2 different radionuclides that date before the time of formation of the solar system.
These 33 are known as primordial nuclides.
Well-known examples are uranium and thoriumbut also included are naturally occurring long-lived radioisotopes, such as potassium Another 50 or so shorter-lived radionuclides, such as radium and radonfound on Earth, are the products of decay chains that began with the primordial nuclides, or are the product of ongoing cosmogenic processes, such as the production of carbon from nitrogen in the atmosphere by cosmic rays.
Radionuclides may also be produced artificially in particle accelerators or What is the process of radiometric hookup reactorsresulting in of these with half-lives of over an hour, and several thousand more with even shorter half-lives. Radioactivity was discovered in by the French scientist Henri Becquerelwhile working with phosphorescent materials.
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 uranium salts caused a blackening of the plate in spite of the plate being wrapped in black paper. These radiations were given the name "Becquerel Rays". It soon became clear that the blackening of the plate had nothing to do with phosphorescence, as the blackening was also produced by non-phosphorescent salts of uranium and metallic uranium.
It became clear from these experiments that there was a form of invisible radiation that could pass through paper and was causing the plate to react as if exposed to light. At first, it seemed as though the new radiation was similar to the then recently discovered X-rays. Further research by Becquerel, Ernest RutherfordPaul VillardWhat is the process of radiometric hookup CurieMarie Curieand others showed that this form of radioactivity was significantly more complicated.
Rutherford was the first to realize that all such elements decay in accordance with the same mathematical exponential formula.
Rutherford and his student Frederick Soddy were the first to realize that many decay processes resulted in the transmutation of one element to another. Subsequently, the radioactive displacement law of Fajans and Soddy was formulated to describe the products of alpha and beta decay.
The early researchers also discovered that many other chemical elementsbesides uranium, have radioactive isotopes. A systematic search for the total radioactivity in uranium ores also guided Pierre and Marie Curie to isolate two new elements: Except for the radioactivity of radium, the chemical similarity of radium to barium made these two elements difficult to distinguish.
After their research on Becquerel's rays led them to the discovery of both radium and polonium, they coined the term "radioactivity". Their exploration of radium could be seen as the first peaceful use of nuclear energy and the start of modern nuclear medicine. The dangers of ionizing radiation due to radioactivity and X-rays were not immediately recognized.
Many people began recounting stories of burns, hair loss and worse in technical journals as early as In February of that year, Professor Daniel and Dr. Dudley of Vanderbilt University performed an experiment involving X-raying Dudley's head that resulted in his hair loss.
A report by Dr. Hawks, of his suffering severe hand and chest burns in an X-ray demonstration, was the first of many other reports in Electrical Review. Other experimenters, including Elihu Thomson and Nikola Teslaalso reported burns.
Thomson deliberately exposed a finger to an X-ray tube over a period of time and suffered pain, swelling, and blistering. Despite this, there were some early systematic hazard investigations, and as early as William Herbert Rollins wrote almost despairingly that his warnings about the dangers involved in the careless use of X-rays were not being heeded, either by industry or by his colleagues.
By this time, Rollins had proved that X-rays could kill experimental animals, could cause a pregnant guinea pig to abort, and that they could kill a fetus. However, the biological effects of radiation due to radioactive substances were less easy to gauge. This gave the opportunity for many physicians and corporations to market radioactive substances as patent medicines. Examples were radium enema treatments, and radium-containing waters What is the process of radiometric hookup be drunk as tonics.
Marie Curie protested against this sort of treatment, warning that the effects of What is the process of radiometric hookup on the human body were not well understood. Curie later died from aplastic anaemialikely caused by exposure to ionizing radiation. By the s, after a number of cases of bone necrosis and death of radium treatment enthusiasts, radium-containing medicinal products had been largely removed from the market radioactive quackery.
The effects of radiation on genes, including the effect of cancer risk, were recognized much later.
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InHermann Joseph Muller published research showing genetic effects and, inwas awarded the Nobel Prize in Physiology or Medicine for his findings.
The committee met inand After World War IIthe increased range and quantity of radioactive substances being handled as a result of military and civil nuclear programmes led to large groups of occupational workers and the public being potentially exposed to harmful levels of ionising radiation.
One Bq is defined as one transformation or decay or disintegration per second.
An older unit of radioactivity is the curieCi, which was originally defined as "the quantity or mass of radium emanation in equilibrium with one gram of radium element ". For radiological protection purposes, although the United States Nuclear Regulatory Commission permits the use of the unit curie alongside SI units,  the European Union European units of measurement directives required that its use for "public health The effects of ionizing radiation are often measured in units of gray for mechanical or sievert for damage to tissue.
Early researchers found that What is the process of radiometric hookup electric or magnetic field could split radioactive emissions into three types of beams. The rays were given the names alphabetaand gammain increasing order of their ability to penetrate matter.