Radioactive The spontaneous emission of radiation

Radioactivity The spontaneous emission of radiations by an element or its compound is called... 

We considered some of the important experiments that led to the discovery and characterization of subatomic particles. Thomson s experiments on the behavior of cathode rays in magnetic and electric fields led to the discovery of the electron and allowed its charge-to-mass ratio to be measured. Millikan s oil-drop experiment determined the charge of the electron. Becquerel s discovery of radioactivity, the spontaneous emission of radiation by atoms, gave further evidence that the atom has a substructure. Rutherford s studies of how thin metal foils scatter a particles led to the nuclear model of the atom, showing that the atom has a dense, positively charged nucleus. 

Radioactivity is the spontaneous emission of radiation from an unstable nucleus. Alpha (a) radiation consists of helium nuclei, small particles containing two protons and two neutrons (fHe). Beta (p) radiation consists of electrons ( e), and gamma (y) radiation consists of high-energy photons that have no mass. Positron emission is the conversion of a proton in the nucleus into a neutron plus an ejected positron, e or /3+, a particle that has the same mass as an electron but an opposite charge. Electron capture is the capture of an inner-shell electron by a proton in the nucleus. The process is accompanied by the emission of y rays and results in the conversion of a proton in the nucleus into a neutron. Every element in the periodic table has at least one radioactive isotope, or radioisotope. Radioactive decay is characterized kinetically by a first-order decay constant and by a half-life, h/2, the time required for the... 

All the nuclear reactions that have been described thus far are examples of radioactive decay, where one element is converted into another element by the spontaneous emission of radiation. This conversion of an atom of one element to an atom of another element is called transmutation. Except for gamma emission, which does not alter an atom s atomic number, all nuclear reactions are transmutation reactions. Some unstable nuclei, such as the uranium salts used by Henri Becquerel, undergo transmutation naturally. However, transmutation may also be forced, or induced, by bombarding a stable nucleus with high-energy alpha, beta, or gamma radiation. 

Radioactivity involves the spontaneous emission of radiation by an unstable nucleus. 

The discovery and the history of radioactivity is closely connected to that of modern science. In 1896 Antoine Henri Becquerel observed and described the spontaneous emission of radiation by uranium and its compounds. Two years later, in 1898, the chemical research of Marie and Pierre Curie led to the discovery of polonium and radium. 

Perhaps Perrin s continuing commitment is explained by the fact that his radiation hypothesis was an update of Marie and Pierre Curie s original explanation of radioactivity, that the apparently spontaneous emission of radiations and charged particles from molecules is activated by immanent radiations. The Curies supposed that radiations in the atmosphere or in the ether disturb the stability of the naturally radioactive elements. This hypothesis, like the radiation hypothesis of chemical activation, eventually succumbed to an explanation using electron configurations, adumbrated by the new quantum interpretation of matter and energy. 

RADIOACTIVITY. The spontaneous disintegration of the nucleus of an atom with the emission of radiation. This phenomenon was discovered by Becquerel in 1896 by the exposure-producing effect on a photographic plate by pitchblende (uranium-containing mineral) while wrapped m black paper in the dark, Soon after this, it was found that uranium minerals and uranium chemicals showed more radioactivity than could be accounted for by the uranium content. About the same dmc. radioactivity of thorium minerals and thorium chemicals was also discovered. 

Spontaneous emission of radiation or particles by a nucleus undergoing decay -> Radioactivity includes the emission of a particles, P particles, and y radiation. 

Radioactivity The spontaneous breakdown of the nucleus of an atom through the emission of particles (alpha and beta particles) and gamma radiation. Although all atomic nuclei can theoretically disintegrate, under normal conditions only a few of the naturally occurring elements such as uranium and radium undergo any significant rate of decay. 

Becquerel presented the problem to Marie and Pierre Curie for further study. Their conclusion was that a nuclear reaction was taking place within the uranium atoms. Marie Curie named this spontaneous emission of radiation by an unstable atomic nucleus radioactivity. 

Nuclei outside the belt of stability, as well as nuclei with more than 83 protons, tend to be unstable. The spontaneous emission by unstable nuclei of particles or electromagnetic radiation, or both, is known as radioactivity. The main types of radiation are a particles (or doubly charged helium nuclei, He " ) /3 particles (or electrons) y rays, which are very-short-wavelength (0.1 nm to 10 " nm) electromagnetic waves positron emission and electron capture. 

Radioactivity. The spontaneous breakdown of an atom by emission of particles and/or radiation. (2.2)... 

In 1896 the French scientist Hemi Becquerel (1852—1908) discovered that a compound of uranium spontaneously emits high-energy radiation. This spontaneous emission of radiation is called radioactivity. At Becquerel s su estion, Marie Curie ( FIGURE 2.6) and her husband, Pierre, began experiments to isolate the radioactive components of the compoimd. 

If the nuclide is radioactive, then the term radionuclide is used. Radioactivity is the spontaneous emission of particles or electromagnetic radiations from a species, either an atom or an ion, consisting of a nucleus surrounded by electrons with a total charge of Z. 

Roentgen s discovery of x-rays stimulated great interest in this new form of radiation worldwide. Antoine Henri Becquerel (1852-1908) accidentally discovered the process of radioactivity while he was studying x-rays. Radioactivity involves the spontaneous disintegration of unstable atomic nuclei. Becquerel had stored uranium salts on top of photographic plates in a dark drawer. When Becquerel retrieved the plates, he noticed the plates contained images made by the uranium salts. Bec-querel s initial discovery in 1896 was further developed by Marie Curie (1867-1934) and Pierre Curie (1859-1906). Marie Curie coined the word radioactive to describe the emission from uranium. 

Radioactivity Spontaneous decay or disintegration of an unstable atomic nucleus accompanied by the emission of radiation. 

Most nuclei in nature are stable and remain intact indefinitely. Radionuclides, however, are unstable and spontaneously emit particles and electromagnetic radiation. Emission of radiation is one of the ways in which an unstable nucleus is transformed into a more stable one that has less energy. The emitted radiation is the carrier of the excess energy. Uranium-238, for example, is radioactive, undergoing a nuclear reaction emitting helium-4 nuclei. The helium-4 particles are known as alpha ( ) particles, and a stream of them is called alpha radiation. When a nucleus loses an alpha particle, the remaining fragment has an atomic number of 90 and a mass number of 234. The element with atomic number 90 is Th, thorium. Therefore, the products of uranium-238 decomposition are an alpha particle and a thorium-234 nucleus. We represent this reaction by the nuclear equation... 

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