Low neutron-capture cross-section

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. 

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... 

Neutron capture processes give rise to the so-called magic-number peaks in the abundance curve, corresponding to closed shells with 50, 82 or 126 neutrons (see Chapter 2). In the case of the s-process, the closed shells lead to low neutron-capture cross-sections and hence to abundance peaks in the neighbourhood of Sr, Ba and Pb (see Fig. 1.4), since such nuclei will predominate after exposure to a chain of neutron captures. In the r-process, radioactive progenitors with closed shells are more stable and hence more abundant than their neighbours and their subsequent decay leads to the peaks around Ge, Xe and Pt on the low-A side of the corresponding s-process peak. 

Uses. Used in various superconductor applications and for cutting tools. Nb steels are very heat resistant. Niobium has a good resistance towards corrosive chemicals even at high temperature it is used in the construction of chemical equipment even if it is not as resistant as tantalum. Nb has a low neutron capture cross-section and it is especially resistant towards liquid sodium corrosion it finds applications in the nuclear industry. Nb is very malleable and easy to shape and may be used in special jewellery this is also because it is possible to give it beautiful colours (thin-film interference colours) by heating in air or, better, by controlled anodization. 

In nuclear reactor technology hafnium-free zirconium(IV) oxide is used as a neutron reflector, due to its low neutron capture cross-section. 

Beryllium oxide is used as a reflector and moderator in nuclear reactors. In addition to its low neutron-capture cross section, BeO has physical, mechanical, and chemical properties that allow its use at elevated temperatures, but its high cost and propensity to damage under irradation have limited its applications " ... 

Properties Dark-gray metal. D 4.47, mp 1500C, bp 2927C. Soluble in dilute acids and potassium hydroxide solution decomposes water. Known only in the tripositive state. Low neutron capture cross section. 

The target material can be a solid, liquid, or gas. For reactor irradiations it is common to place the target material in a container of polypropylene or of some metal of relatively low neutron capture cross-section. Pyrex and soda glass are not good materials because of the reactions (n,a) Li (which has a large Na(n,y) Na (which yields a... 

Aluminum, with its low neutron capture cross section is the preferred cladding material for moderate temperature ranges. 

Cr-Fe-Zr is one of the ternary systems relevant to Zircaloys, which arc widely used as fuel cladding material in nuclear industry due to their low neutron-capture cross-section, high mechanical strength, high thermal conductivity and good corrosion resistance. In fliese alloys Fe and Cr, which are essentially insoluble in Zr at temperatures lower than about 600°C, are present in flie form of Zr(Fe,Cr)2 precipitates. This is one of the reasons why several studies have been performed on properties and characteristics of the Zr(Fe, Cr)2 phase. 

Because of its low neutron-capture cross-section and high resistance to corrosion, the manufacture of high-grade zirconium, free from hafnium, has been developed to a great extent in the U.S.A. for use in pressurized water reactors. 

Answer Because of their chemical Inertness, low neutron capture cross sections, and desirable heat transfer characteristics. Helium is completely inert chemically and is a very good conductor of heat, carbon dioxide is useful at low teogperatures because it is a poor heat conductor. 

Reed (1971) has grown large crystals of the low neutron capture cross-section... 

The most interesting fields of application of niobium, tantalum and their alloys are heat exchangers, heat protection shields in furnaces, chemical equipment and aerospace materials. Due to the relatively low neutron capture cross section, niobium may have some interest in nuclear applications. 

Uranyl fluoride. Uranyl fluoride is a very attractive fuel solute because of the low neutron capture cross-section of fluorine. However, at high temperatures it undergoes hydrolysis, which means that excess HF would be required to maintain homogeneity. Hydrogen fluoride is also a component of the vapor phase. Both liquid and vapor are very corrosive toward zirconium and titanium, but less corrosive toward stainless steel (see Article 5-3.3). Figure 3-11 shows the phase relationships in this system [14],... 

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