Radioactive decay The process by which

Radioactive decay The process by which unstable nuclei become more stable. 

Radioactive decay the process by which radioactive isotopes emit radiation. Each isotope has a characteristic decay pattern in terms of the type of radiation emitted and its half-life... 

Radioactivity is a natural and spontaneous process that occurs when unstable atoms of an element emit or radiate excess energy in the form of particles or waves. Such emissions are called ionizing radiation. Ionization, the process by which molecules lose electrons, is a particular characteristic of the radiation produced when radioactive elements decay. The capacity of... 

For efficient release of radon into the air spaces of soil, the radon atom must be formed within 20-70 nm of the mineral surface for most common minerals. This distance is the recoil range of a radon atom at the instant of its formation from the decay of radium. The processes by which radon atoms escape from a given material are referred to as radon emanation. The emanation power or the coefficient of emanation is defined as the ratio of the number of radon atoms that escape from the solid to the number of radon atoms formed by radioactive decay of radium in the solid. The emanation power varies from about 0.02 to 0.7, depending upon the mineral structure and the water content. 

Radioactive dating is the process by which the approximate age of an object is determined based on the amount of certain radioactive nuciides present. Such an estimate is based on the fact that radioactive substances decay with known half-lives. Age is estimated by measuring either the accumulation of a daughter nuclide or the disappearance of the parent nuclide. 

Another environmental factor which affects thermoplastics is radiation. Most people think of the term radiation as it pertains to radioactivity, which describes a material which emits particles and energy as part of nuclear decay. But radiation is actually a much broader term, and describes the process by which electromagnetic waves travel through space. 

Uranium-235 and U-238 behave differently in the presence of a controlled nuclear reaction. Uranium-235 is naturally fissile. A fissile element is one that splits when bombarded by a neutron during a controlled process of nuclear fission (like that which occurs in a nuclear reactor). Uranium-235 is the only naturally fissile isotope of uranium. Uranium-238 is fertile. A fertile element is one that is not itself fissile, but one that can produce a fissile element. When a U-238 atom is struck by a neutron, it likely will absorb the neutron to form U-239. Through spontaneous radioactive decay, the U-239 will turn into plutonium (Pu-239). This new isotope of plutonium is fissile, and if struck by a neutron, will likely split. 

The numerical combination of protons and neutrons in most nuclides is such that the nucleus is quantum mechanically stable and the atom is said to be stable, i.e., not radioactive however, if there are too few or too many neutrons, the nucleus is unstable and the atom is said to be radioactive. Unstable nuclides undergo radioactive transformation, a process in which a neutron or proton converts into the other and a beta particle is emitted, or else an alpha particle is emitted. Each type of decay is typically accompanied by the emission of gamma rays. These unstable atoms are called radionuclides their emissions are called ionizing radiation and the whole property is called radioactivity. Transformation or decay results in the formation of new nuclides some of which may themselves be radionuclides, while others are stable nuclides. This series of transformations is called the decay chain of the radionuclide. The first radionuclide in the chain is called the parent the subsequent products of the transformation are called progeny, daughters, or decay products. 

Although we have found that for internal noise the Ito-Stratonovich dilemma is undecidable for lack of a precise A(t) there are cases in which the Ito equation seems the more appropriate option. As an example we take the decay process defined in IV.6 the M-equation is (V.1.7) and the average obeys the radioactive decay law (V.1.9). As the jumps are relatively small one may hope to describe the process by means of a Langevin equation. Following the Langevin approach we guess... 

Iodine is lost from herbage by the same processes which cause field loss of Sr, 137Cs and other nuclides (Section 2.13). There is also the possibility of revolatilisation of iodine. If XG is the rate constant of field loss (fraction of iodine per unit area of ground lost from vegetation per second) and X1 the rate constant of radioactive decay, the combined apparent or effective loss rate is XE = XG + Xt. The effective half-life is Te = 0.693/A . The use of the term half-life implies that field loss is exponential and TE invariant with time, which is not always true. 

Figure 1 Schematic illustration of the production and fate of Th in seawater. Radioactive decay of dissolved produces Th that initially exists as a dissolved species. Dissolved Th may either undergo radioactive decay to Ra, or it may be adsorbed to particles. Radioactive decay is represented by a decay constant, A (A = ln(2)/radioactive half-life)), and uptake by particles (scavenging) is represented by a first-order rate constant, k. Th is initially sorbed by small slowly settling particles (supersript s ), which form the vast majority of partiele mass in the ocean. Th sorbed to small particles may undergo radioactive decay to Ra it may desorb (return to solution, represented by the first-order rate eonstant -i) or it may sink from the water colunm, where the loss of particulate Th is represented by the first-order rate constant 2-Similar processes influence " Th, which is produced by radioactive decay of and which...

Such a chemical reaction, in which molecules are not colliding with other atoms or molecules, is called a first-order reaction because the rate at which chemical concentration changes at any instant in time is proportional to the concentration raised to the first power. Certain chemical processes, such as radioactive decay, are described by first-order kinetics. In the absence of any other sources of the chemical, first-order kinetics may lead to exponential decay or first-order decay of the chemical concentration (i.e., the concentration of the parent compound decreases exponentially with time) ... 

Secular equilibrium will be obtained only if the system in question remains physically closed, such that radioactive decay is the only process by which a daughter is effectively removed from its parent. Any additional non-radiochemical process that physically removes the daughter will destroy secular equilibrium. We shall see that chemical separation mechanisms prevent a closed system, and this is necessary for useful rate information to be obtained from the radioactive decay series. 

The other more short-lived actinides must be made synthetically by using high-energy collisions in a particle accelerator. These machines collide a particle such as a gamma ray with an atom of the naturally formed actinide elements. They split after collision the other elements are formed in the process of radioactive decay. The first of these new elements were named after the planets in a similar fashion to uranium (planet Uranus) — neptunium (Neptune) and plutonium (Pluto). The rest have been named for historical themes or places in which they were first created. 

The difference between the X and y regions is one of scale and the methods by which the photons are produced. X-rays are emitted by some radioactive elements, but are mainly produced by directing a beam of cner tic i.e. accelerated) electrons on to a metal surface (e.g. copper). y-Rays are generally emitted as the result of secondary processes following the primary decay of a radioactive element, i.e. the primary... 

As researchers performed experiments that advanced them along the row of actinide elements on the Periodic Table, the general trends with increasing atomic number were smaller production probabilities expressed as cross sections (a consequence of the diminishing fission barrier and higher fission probabilities), an increased probability of decay by a-particle emission (a consequence of increasing a-decay Q values) and shorter half-lives. For the elements below fermium, spontaneous fission is not an important decay mode. Experimental work was dominated by radiochemical techniques in which atomic number was determined by chemical properties and atomic mass was determined by mass spectrometry and the connections of nuclei to one another by the processes of radioactive decay. The physical separation and detection methods that were used in later work were developed in the 1960s. 

Certain interactions with matter of the radiation accompanying the decay of unstable nuclides (a- and /9-particles, y rays) are the basis for the detection and measurement of radioactivity These include photochemical processes, by which a radioactive sample placed in close contact with photographic emulsion causes blackening of the latter upon development (autoradiography) gas ionisation and the deriving production of current pulses that can be analysed and measured by suitable devices excitation of orbital electrons of special molecules, either in a crystalline form or in solution, with subsequent emission of light pulses to be converted into electric current by a photoelectric detector (scintillation)... 

Atoms of elements are composed of protons, neutrons, and electrons. Only certain combinations of protons and neutrons yield stable nuclides all other combinations are unstable. Radioactive decay is the process in which an unstable nucleus either ejects or captures particles transforming the radioactive nuchde into another element. In some cases the daughter nuchde produced by radioactive decay also is unstable and radioactive decay continues through as maity steps as necessary to prodnce a stable nuclide. 

Radon occurs only in trace amounts, its longest-lived isotope being Rn. It is produced by the a-decay of Ra, which is itself just one of the radioactive isotopes produced in the chain of decay processes by which is transformed into Pb. The Rn is itself a-active ... 

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