Boron nuclear properties

The section on Spectroscopy has been retained but with some revisions and expansion. The section includes ultraviolet-visible spectroscopy, fluorescence, infrared and Raman spectroscopy, and X-ray spectrometry. Detection limits are listed for the elements when using flame emission, flame atomic absorption, electrothermal atomic absorption, argon induction coupled plasma, and flame atomic fluorescence. Nuclear magnetic resonance embraces tables for the nuclear properties of the elements, proton chemical shifts and coupling constants, and similar material for carbon-13, boron-11, nitrogen-15, fluorine-19, silicon-19, and phosphoms-31. 

Boron carbide is a non-metallic covalent material with the theoretical stoichiometric formula, B4C. Stoichiometry, however, is rarely achieved and the compound is usually boron rich. It has a rhombohedral structure with a low density and a high melting point. It is extremely hard and has excellent nuclear properties. Its characteristics are summarized in Table 9.2. 

Boron carbide (B4C) is extremely hard and is used where maximum resi stance to erosion is required. It has good nuclear properties (see Ch. 9). 

At low temperatures (15 million K), reactions between helium nuclei are inhibited by electrical repulsion. On the other hand, the nuclear properties of lithium, beryllium and boron nuclei (Z = 3,4, 5), and in particular their stability, are such that they are extremely fragile, decaying at temperatures of only 1 million K. For this reason, they are not formed in appreciable quantities in stars and cannot serve to bridge the gap between helium and carbon, species noted for their nuclear stability but which, it should be recalled, occur only in minute amounts in nature. 

The electrical properties of the diamond films or free-standing discs are largely determined by the boron-doping level. Resistivities of useful diamond OTEs are in the range of 0.5-0.05 H-cm. Boron-doping levels associated with this resistivity are ca. 1-10 x 10 B/cm, as determined by boron nuclear reaction analysis measurements. Very preliminary Hall effect measurements for the diamond/quartz (Fig. 23A, 2) and diamond/ Si (Fig. 23B, 7) OTEs have revealed carrier concentrations between 10 and 10 cm and carrier mobilities (holes are the majority carrier in boron-doped films) of 1-100 cm /V-s. 

The characteristics and properties of boron carbide are summarized in Table 8.2 (for structural data, see Table 7.5 of Ch. 7). They are reviewed in more detail in Secs. 4-8. The material has outstanding hardness and excellent nuclear properties (see Sec. 7.0). 

Table 2.1 Nuclear properties of hydrogen, carbon and boron isotopes.

Besides these physical and chemical properties, boron has nuclear properties that add to its usefulness. Boron-10 absorbs neutrons efficiently. Note that the products of this absorption, shown in Equation (14.12), are nonradioactive isotopes of hehum and Hthium ... 

The predominance of the +1 state in the heavier congeners is underscored by a consideration of the standard reduction potentials. Boron displays some strikingly different structures ranging from the Bj2 aUotrope of the semimetal through the variety of binary borides to the various ortho-, meta-, and three-dimensional borates. The nuclear properties of boron-10 add to the general usefulness of these structures. 

The presence of non-metal lie elements in metals may affect their properties in a variety of ways. Non-metals may influence mechanical and physical properties such as corrosion resistance, hardness, hot and cold ductility, mechanical strength, conductivity, castability, nucleus forming properties and sinterability. Boron influences the nuclear properties of metals. These effects may be felt at very low concentrations even below 0.1 i g/g. 

The isotope boron-10 is used as a control for nuclear reactors, as a shield for nuclear radiation, and in instruments used for detecting neutrons. Boron nitride has remarkable properties and can be used to make a material as hard as diamond. The nitride also behaves like an electrical insulator but conducts heat like a metal. 

Low sulfur and ash levels are required for high GTE, isotropic cokes used for carbon and graphite specialty products. Highly isotropic cokes are also the filler materials for producing graphite for nuclear reactors. The purity, particularly the boron content, is critical in this appHcation. Properties of typical needle and isotropic (regular) cokes are summarized in Table 1. 

Boron has high neutron absorption and the boron-aluminum composites are being investigated for nuclear applications. Single-ply boron-epoxy composites have microwave polarization properties with potential applications in antenna and radome designs. 01... 

Nuclear relaxation rates, iron-sulfur proteins, 47 267-268 Nuclear resonance boron hydrides and, 1 131-138 fluorescence, 6 438-445 Nuclear spin levels, 13 140-145 Magnetic properties of nuclei, 13 141-145 Nuclear testing... 

One of its two stable isotopes, 10B, is such a good absorber of neutrons that it is used in control rods in nuclear reactors. This property also makes it useful for construction of neutron detectors. Boron is used to make windows that are transparent to infrared radiation, for high-temperature semiconductors, and for electric generators of a thermoelectric type. 

In brief, then, silicon is an electropositive element with some of the properties of the metals. It commonly exhibits a covalency of four, but is capable of a maximum covalency of six in combination with atoms of relatively small volume and high nuclear charge. Chemically it resembles boron and germanium as closely as carbon and shows an exceptionally strong preference for combination with oxygen. 

Boron carbide is a relatively inexpensive hard material, which is used for its mechanical properties of strength and extreme hardness in armor-plates for body protection, in sandblast nozzles, and as an abrasive for grinding and cutoff wheels. In nuclear plants, boron carbide is used as the neutron absorbing material of the control rods. 

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