Atoms nuclear theory

The MO theory differs greatly from the VB approach and the basic MO theory is an extension of the atomic structure theory to molecular regime. MOs are delocalized over the nuclear framework and have led to equations, which are computationally tractable. At the heart of the MO approach lies the linear combination of atomic orbitals (LCAO) formahsm... 

During the last few years the study of spectra of heavy and superheavy elements (atoms and ions) has been of great interest for further development in atomic and nuclear theories [1-12]. Theoretical methods used to calculate the spectroscopic characteristics of heavy and superheavy ions may be divided into... 

Nonrelativistic quantum mechanics, extended by the theory of electron spin and by the Pauli exclusion principle, provides a reliable theory for the computation of atomic spectral frequencies and intensities, of cross sections for scattering or capture of electrons by atomic systems, of chemical bonds and many properties of solids, including magnetic properties, although with much more complicated systems it has not always proved possible to develop with adequate accuracy the consequences of the theory. Quantum mechanics has also had a limited success in nuclear theory although m this field it is possible that a more fundamental system of mechanics is required. 

Although the material contained in this book concerns the theory of many-electron atoms and ions, its many ideas and methods (e.g., graphical methods, quasispin and isospin techniques, particle-hole formalism, etc.) are fairly universal and may be easily applied (or already are) to other domains of physics (nuclear theory, elementary particles, molecular, solid state physics, etc.). 

Wheeler, J.A. Fission Physics and Nuclear Theory . In Proceedings of the International Conference on the Peaceful Uses of Atomic Energy , Geneva,... 

From the beginning of his studies Langmuir was especially interested in the structure of the atom. The nature of the atom s structure was still very much in doubt. Many had crossed swords with nature to wrest this secret from her. Kelvin had pictured the atom as consisting of mobile electrons embedded in a sphere of positive electrification. J. J. Thomson had developed this same idea but his model, too, had failed because it could not account for many contradictory phenomena. Rutherford s nuclear theory of the atom as a solar system was also objected to as incomplete. The greatest difficulty to the acceptance of these models was that they all lacked a consistent explanation of the peculiar spectra of gaseous elements when heated to incandescence. 

The nuclear theory of atomic structure, put forward by Rutherford, regarded the electrons as moving in orbits round the nucleus. The dynamical theory of this system was developed by Bohr, who found it necessary to supplement classical mechanics by the quantum mechanics of Planck. According to classical theory, a system consisting of an electron moving in a circular orbit round a nucleus, to which it is attracted according to Coulomb s law, would lose energy, with the result that the electron would approach and finally collide with the nucleus. Thus on the basis of classical theory, the Rutherford atom would only be stable for about io seconds, after which time the electron would have fallen into the nucleus. 

After Ernest Rutherford (1871-1937) discovered the atomic nucleus in 1911, he proposed the name proton for the very lightest of all nuclei the nucleus of the ordinary hydrogen atom. Proto- is Greek for first. In 1932, when James Chadwick (1891-1974) discovered another particle in the nucleus that was very similar to the positive proton except that it was electrically neutral, it was natural for him to call it a neutron. It was then equally natural to call both nuclear particles nucleons, especially when nuclear theory began to treat the proton and the neutron as two different states of the same fundamental particle. 

Geiger, Hans Wilhelm (1882-1945) German physicist, who carried out research with Rutherford at Manchester University before returning to Germany in 1912. In 1908 he and Rutherford produced the Geiger counter, improved in 1928 as the Geiger-Mtiller counter. In 1909 his scattering experiments with alpha particles led to Rutherford s nuclear theory of the atom. 

But if we are concerned with more complex aspects of nuclear structure, the liquid drop model of the nucleus won t do. Suppose we are interested, for example, in the pattern of stability and instability that governs the collection of nuclear isotopes. Why is there a line of stability about which the stable nuclei are concentrated, with deviation from that line, which is plotted with numbers of protons and numbers of neutrons as axes, indicating the likelihood that the nucleus in question will be unstable Much insight can be gained from a model that treats the nucleons in the nucleus as moving on orbits in an overall potential field. Here, the nucleons are treated as if they were like the electrons in their orbits that surround the nucleus in the atom. Numbers are assigned that are parallels to the familiar quantum numbers of atomic electron theory, and orbits for the nucleons in the nucleus characterized by these quantum numbers are posited. Just... 

In this paper we have attempted to couple modem atomic theories with an ancient guiding principle. In particular, a parallel between atomic, nuclear and cluster shells is carried out using a fundamental concept of the Pythagorean school known as the gnomon. 

Rutherford created a new model to explain his results ( Figure 4.5). He concluded that matter must not be as uniform as it appears. It must contain large regions of empty space dotted with small regions of very dense matter. In order to explain the deflections he observed, the mass and positive charge of an atom must all be concentrated in a space much smaller than the size of the atom itself. Based on this idea, he developed the nuclear theory of the atom, which has three basic parts ... 

Rutherford s nuclear theory was a success and is still valid today. The revolutionary part of this theory is the idea that matter—at its core—is much less uniform than it appears. If the nucleus of the atom were the size of tiiis dot , the average electron would be about 10 m away. Yet the dot would contain almost the entire mass of the atom. Imagine what matter would be like if atomic structure broke down. What if matter were composed of atomic nuclei piled on top of each other like marbles Such matter would be incredibly dense a single grain of sand composed of solid atomic nuclei would have a mass of 5 million kg (or a weight of about 10 million lb). Astronomers believe that black holes and neutron stars are composed of this kind of incredibly dense matter. 

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