Nuclides

This chapter summarizes those aspects of nuclear physics and radiochemistry that are essential to an understanding of the chemical technology associated with nuclear reactors. No attempt is made to treat these subjects completely. A selected list of texts on nuclear physics and radiochemistry is given at the end of this chapter. 

A neutral atom consists of a small, dense central nucleus, about 10 cm in diameter, surrounded by a diffuse cloud of electrons whose outside diameter is around 10 cm. The nucleus contains most of the mass of the atom and carries a positive electric charge that equals a whole number times the electronic charge, 1.602101 X 10 C. This whole number is called the atomic number Z of the atom. It is identical with the serial number of the element in the periodic table. Each nucleus is made up of Z protons and a definite number N of neutrons. The total number of particles in the nucleus, N- Z, is called the mass number and is denoted by A. The mass number turns out to be the whole number nearest to the atomic weight of the nuclide. 

In the published charts of the nuclides and in the compilation in App. C, the atomic masses are listed in physical mass units (amu), in which one atom of has a mass of 

It is characteristic of nuclear reactions of the type occurring in nuclear reactors that the sum of the number of neutrons and protons in the reactants equals the sum in the products. The same is true of the charge of the reactants and products. Consequently, in balancing nuclear reactions, the sum of the s of the reactants must equal the sum of the. 4 s of the products and the sum of the Z s of the reactants must equal the sum of the Z s of the products. As an example of a balanced equation for a nuclear reaction, we may consider one of the fission reactions that occurs when absorbs a neutron  

The neutron is represented by in, a nuclide with nuclear charge 0 and mass number 1. 

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The NDT and TD methods and means that solve the proplems connected with the necessaty to find the arms, explosives, radioactive and nuclide sources as well as to detect false documents and securities are rapidly developing. 

To find the radioactive and nuclide sources Dosimeters, radiometers, gamma-signaling devices, spectrometers... 

The equation describes the manner in which the nuclear magnetization, M, at position r and time t processes about the magnetic flux density, B, in which it is found. The constant y is the magnetogyric ratio of the nuclides under study. The precessional frequency, co, is given by the Lannor equation. 

Krypton-85 has been used for over 25 years to measure the density of paper as it is amanufactured. The total weight of paper can be controlled to a very accurate degree by the use of krypton 85 and other radioactive nuclides. The common name for such a device is a beta gague that can measure the thickness of a material. 

Amount of substance mole mol Amount of substance which contains as many specified entities as there are atoms of car-bon-12 in exactly 0.012 kg of that nuclide. The elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles. 

TABLE 4.16 Table of Nuclides Explanation of Column Headings... 

Nuclide. Each nuclide is identified by element name and the mass number A, equal to the sum of the numbers of protons Z and neutrons N in the nucleus. The m following the mass number (for example, Zn) indicates a metastable isotope. An asterisk preceding the mass number indicates that the radionuclide occurs in nature. Half-life. The following abbreviations for time units are employed y = years, d = days, h = hours, min = minutes, s = seconds, ms = milliseconds, and ns = nanoseconds. 

Natural abundance. The natural abundances listed are on an atom percent basis for the stable nuclides present in naturally occurring elements in the earth s crust. 

Thermal neutron absorption cross section. Simply designated cross section, it represents the ease with which a given nuclide can absorb a thermal neutron (energy less than or equal to 0.025 eV) and become a different nuclide. The cross section is given here in units of barns (1 barn = 10 cm ). If the mode of reaction is other than ( ,y), it is so indicated. 

Nuclide Natural abundance, % Spin I Sensitivity at constant field relative to NMR frequency for a 1-kG field, Mffz Magnetic moment J-T-1 Electric quadrupole moment Q, 10 m ... 

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