Emission, of radiation spontaneous

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. 

The intensity of a spontaneous emission of radiation by an atom is given by the equation Ifm (L3)... 

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... 

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

Spontaneous emission of radiation from an electronically and/or vibrationally excited species not in thermal equilibrium with its environment is called luminescence when the emission is accompanied by the formation of a molecular entity of the same spin multiplicity it is called fluorescence (F), whereas luminescence involving change in spin multiplicity (typically from triplet to singlet) is called phosphorescence (Ph) [1],... 

Fluorescence Spontaneous emission of radiation (luminescence) from an excited molecular entity with the formation of a molecular entity of the same spin multiplicity. 

Luminescence Spontaneous emission of radiation from an electronically or vibra-tionaUy excited species not in thermal equilibrium with its environment... 

Just as with quantum yields, there are basically two different kinds of lifetimes, one a result of direct experimental measurement, and the other a derived quantity. These have not always been carefully distinguished. Moreover, the same quantity has been labeled by a variety of names and symbols. For example, radiative lifetime, true radiative lifetime, natural lifetime, intrinsic lifetime, and inherent lifetime all mean the same thing the lifetime a molecule in an excited state would have if there were no steps competing with that of spontaneous emission of radiation. 

If the spontaneous emission of radiation of the appropriate energy is the only pathway for a return to the initial state, the average statistical time that the molecule spends in the excited state is called the natural radiative lifetime. For an individual molecule the probability of emission is time-independent and the total intensity of emission depends on the number of molecules in the excited state. In a system with a large number of particles, the rate of decay follows a first-order rate law and can be expressed as... 

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. 

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

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. 

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

Fluorescence6,30 is the spontaneous emission of radiation by an excited molecule, typically in the first excited singlet state Si, with retention of spin multiplicity. 

The term luminescence denotes the spontaneous emission of radiation from an electronically excited species and comprises fluorescence and phosphorescence, and also chemiluminescence (Section 5.6). 

Our treatment does not include the phenomenon of spontaneous emission of radiation. Its extension to include this is not easy Dirac s treatment is reasonably satisfactory, and we may hope that the efforts of theoretical physicists will soon provide us with a thoroughly satisfactory discussion of radiation. For the present we content ourselves with using Equation 40-56 in combination with the above equations to obtain... 

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. 

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. 

Enhanced spontaneous emission of radiation from Rydberg atoms was reported in 1983 by Goy et al.t59], in this experiment excited sodium atoms (in the 23S state) were formed within a superconducting cavity resonant at 3 0 GHz. This frequency closely corresponds to the... 

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. 

The rate of spontaneous emission of radiation for a transition from a state n to n is given by the Einstein A coefficient ... 

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