Capture-cross section

The simplest theoretical description of the photon capture cross-section is given by Fermi s Golden Rule... 

Gadolinium has the highest thermal neutron capture cross-section of any known element (49,000 barns). 

Several portions of Section 4, Properties of Atoms, Radicals, and Bonds, have been significantly enlarged. For example, the entries under Ionization Energy of Molecular and Radical Species now number 740 and have an additional column with the enthalpy of formation of the ions. Likewise, the table on Electron Affinities of the Elements, Molecules, and Radicals now contains about 225 entries. The Table of Nuclides has material on additional radionuclides, their radiations, and the neutron capture cross sections. 

Determination of gold concentrations to ca 1 ppm in solution via atomic absorption spectrophotometry (62) has become an increasingly popular technique because it is available in most modem analytical laboratories and because it obviates extensive sample preparation. A more sensitive method for gold analysis is neutron activation, which permits accurate determination to levels < 1 ppb (63). The sensitivity arises from the high neutron-capture cross section (9.9 x 10 = 99 barns) of the only natural isotope, Au. The resulting isotope, Au, decays by P and y emission with a half-life of 2.7 d. 

For nuclear applications, the cadmium and boron (high capture cross-section elements) shall be defined as cadmium, max % 0.0001 or 0.00005 boron, max % 0.00007 or 0.00003. 

Isotope CAS Registry Number Occurrence, % Thermal neutron capture cross section, 10-" ... 

Graphite is chosen for use in nuclear reactors because it is the most readily available material with good moderating properties and a low neutron capture cross section. Other features that make its use widespread are its low cost, stabiHty at elevated temperatures in atmospheres free of oxygen and water vapor, good heat transfer characteristics, good mechanical and stmctural properties, and exceUent machinabUity. 

Neutron economy in graphite occurs because pure graphite has a neutron capture cross section of only 0.0032 0.002 x lO " cm. Taking into account the density of reactor grade graphite (bulk density 1.71 g/cm ), the bulk neutron absorption coefficient is 0.0003/cm. Thus a slow neutron may travel >32 m in graphite without capture. 

The only large-scale use of deuterium in industry is as a moderator, in the form of D2O, for nuclear reactors. Because of its favorable slowing-down properties and its small capture cross section for neutrons, deuterium moderation permits the use of uranium containing the natural abundance of uranium-235, thus avoiding an isotope enrichment step in the preparation of reactor fuel. Heavy water-moderated thermal neutron reactors fueled with uranium-233 and surrounded with a natural thorium blanket offer the prospect of successful fuel breeding, ie, production of greater amounts of (by neutron capture in thorium) than are consumed by nuclear fission in the operation of the reactor. The advantages of heavy water-moderated reactors are difficult to assess. 

The capture cross section of Li for this reaction using thermal neutrons is 930 x 10 (930 b) (43). AU of the experimental data available to the end of... 

Production in Heavy Water Moderator. A small quantity of tritium is produced through neutron capture by deuterium in the heavy water used as moderator in the reactors. The thermal neutron capture cross section for deuterium is extremely small (about 6 x 10 consequendy the... 

Nickel-manganese-palladium brazes are resistant to attack by molten alkali metals and And applications in sodium-cooled turbine constructions. Their freedom from silver and other elements of high thermal neutron-capture cross-section allows them to be used in liquid-metal-cooled nuclear reactors. 

Zirconium alloys have been much less thoroughly studied than titanium alloys. The main application of interest has been for nuclear reactor components where good corrosion resistance combined with a low neutron capture cross-section has been required. Corrosion fatigue crack growth in these alloys in high temperature (260-290°C) aqueous environments typical of... 

Negative Cl can give excellent results for certain types of compounds. Compounds with electronegative substituents and unsaturation can be expected to have a large electron capture cross-section and thus work well in the negative ion mode. Frequently, much higher sensitivity is obtained for these compound types in the negative ion mode than under positive ion conditions. In addition, the molecular ion is usually very abundant. The... 

Boric acid [B(OH)3] is employed in primary coolant systems as a soluble, core reactivity controlling agent (moderator). It has a high capture cross-section for neutrons and is typically present to the extent of perhaps 300 to 1,000 ppm (down from perhaps 500 to 2,500 ppm 25 years ago), depending on nuclear reactor plant design and the equilibrium concentration reached with lithium hydroxide. However, boric acid may be present to a maximum extent of 1,200 ppm product in hot power nuclear operations. 

Niobium (also known as columbium) is a soft, ductile, refractory metal with good strength retenti on at high temperature, and a low capture cross-section for thermal neutrons. Itis readily attacked by oxygen and other elements above 200°C. CVD is used to produce coatings or free standing shapes. The properties of niobium are summarized in Table 6.8. 

The interesting feature of mixed 7T-ring carbonyl compounds lies in the possibility of observing competitive reactions between the two ligands. As yet very few systems have been studied, largely because such systems seldom have a favorable combination of chemical properties (stability and easy separability of all expected compounds) and nuclear properties (capture cross section, half-life, and radiation energy). 

Table 4. Single-electron capture cross-sections on the n = 3 levels (in 10 cm ). (For comparison with Dijkkamp results, the collision energy is given in parenthesis...

Table 5. Values of the single-electron capture cross-sections for the and states (in 10" cm ).

Assuming the contribution of the potential energy curves which have not been taken into account to be almost constant with the collision energy, such calculations could provide a relative estimate of the variation of the double capture cross-sections with the collision energy. The results presented in Fig. 7 seem to be coherent with this hypothesis and to corroborate a cascade effect for the double electron capture process. 

Attree RW, Cabell MJ, Cushing RL, Pieroni JJ (1962) A calorimetric determination of the half-life of thorium-230 and a consequent revision to its neutron capture cross section. Can J Phys 40 194-201 Bateman H (1910) Solution of a system of differential equations occurring in the theory of radioactive transformations. Proc Cambridge Phil Soc 15 423-427 Beattie PD (1993) The generation of uranium series disequilibria by partial melting of spinel peridotite ... 

Boron nitride, in view of its unique properties, namely absence of electrical conductivity, oxidation resistance, optical transparency, and high neutron capture cross-section for special applications, offers advantages over other ceramics. Thus, for the... 

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