Thermal-neutron absorption cross section

NucUde Half-life (S = stable) Atoms per fission-product pair Effective thermal cross sections, b Neutron absorption, bams per fission-product pair... 

Beryllium is used in nuclear reactors as a reflector or moderator for it has a low thermal neutron absorption cross section. 

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. 

Zirconium is used as a containment material for the uranium oxide fuel pellets in nuclear power reactors (see Nuclearreactors). Zirconium is particularly usehil for this appHcation because of its ready availabiUty, good ductiUty, resistance to radiation damage, low thermal-neutron absorption cross section 18 x 10 ° ra (0.18 bams), and excellent corrosion resistance in pressurized hot water up to 350°C. Zirconium is used as an alloy strengthening agent in aluminum and magnesium, and as the burning component in flash bulbs. It is employed as a corrosion-resistant metal in the chemical process industry, and as pressure-vessel material of constmction in the ASME Boiler and Pressure Vessel Codes. 

Atomic number Atomic weight Crystal structure Melting Density Thermal Electrical resistivity (at 20°C) Temperature coefficient of resistivity Specific Thermal Standard electrode potential Thermal neutron absorption cross-section. 

Density (g/cm Melting point ( Q Boiling point (°C) Thermal neutron absorption cross section (barn/atom) Linear , Thermal coeff. of conductivity 7 7 (W/cm C) Specific heat (J/g°C) Electrical resistivity (ufl/cm) Temperature coeff. of resistivity (°C)... 

Thermal neutron, absorption cross section barn/atom (cm2/cm3) 0.059 (0.00254)... 

Zirconium is used for structural parts in the core of water moderated nuclear reactors to this end Zr has several good properties and especially it has low thermal neutron cross-section. Hf, on the contrary, has a high thermal neutron absorption coefficient, so it is necessary to be able to prepare Hf-free zirconium. On the other hand, in some cases the Hf properties too may be useful in nuclear technology, in the control rods of submarine reactors. 

Grayish metal hexagonal close-packed crystal system, lattice constant, a=2.286 A and c=3.584 A density 1.85 g/cm permeable to x-rays highly ductile modulus to weight ratio very high, elastic modulus 44.5 x 10 at 25°C (for hot-pressed block and sheet) melting point 1,287°C vaporizes at 2,471°C sound transmission velocity 12,600 m/sec reflectivity (white hght) 55% thermal neutron absorption cross-section 0.0090 barns/atom electrode potential, Be/Be2+(aq) 1.85 V electrical resistivity 3.36 x 10-i° ohm.m (at 20°C). 

The most important apphcation of this metal is as control rod material for shielding in nuclear power reactors. Its thermal neutron absorption cross section is 46,000 bams. Other uses are in thermoelectric generating devices, as a thermoionic emitter, in yttrium-iron garnets in microwave filters to detect low intensity signals, as an activator in many phosphors, for deoxidation of molten titanium, and as a catalyst. Catalytic apphcations include decarboxylation of oxaloacetic acid conversion of ortho- to para-hydrogen and polymerization of ethylene. 

Colorless or light yellow metal at ordinary temperatures it occurs in hexagonal close-packed crystalline form, known as alpha-gadolinium alpha form transforms to a body-centered cubic allotropic form, beta-gadolinium upon heating at 1,262°C density 7.90 g/cm melting point 1,313°C vaporizes at 3,266°C vapor pressure 9.0 torr at 1,800°C (calculated) electrical resistivity 134.0 microhm-cm at 25°C Poisson ratio 0.259 modulus of elasticity 8.15x106 psi thermal neutron absorption cross section 46,000 barns insoluble in water dissolves in acid (reacts). 

Occurs as a close-packed hexagonal alpha-form and a hody-centered cubic beta modification melting point 2,233°C vaporizes at 4,602°C electrical resistivity 35.5 microhm-cm at 20°C magnetic susceptibility 0.42xlCL6 emu/g at 25°C thermal neutron absorption cross section 105 barns/atom work function 3.5 eV modulus of elasticity 20x10 psi tensile strength 58,000 psi at 25°C insoluble in water, dilute mineral acids and nitric acid at all concentrations soluble in hydrofluoric acid, concentrated sulfuric acid and aqua regia. 

Silver-white lustrous soft metal highly malleable and ductile face-centered tetragonal crystalline structure (a=4.583A, c=4.93GA) diamagnetic metal density 7.31 g/cm at 20°C melts at 156.6°C vaporizes at 2,072°C electrical resistivity 8.4 x Kh ohm-cm superconducting at 3.38°K (—269.8°C) hardness 0.9 (Brinnel) tensile strength 26.19 atm modulus of elasticity 10.8 GPa thermal neutron absorption cross-section 190 10 bams soluble in acids. 

Silvery-white metal close-packed cubic crystals lattice constant 3.8394A at 20°C density 22.42 g/cm (highest among metals) melts at 2410°C vaporizes at 4,130°C hardness 6-6.5 Mohs electrical resistivity 4.71 j,ohm-cm Young s modulus 3.75 x 10 tons/in magnetic susceptibility 0.133 x 10 cm3/g thermal neutron absorption cross section 440 barns. 

Soft white, ductile metal high-purity metal is very ductile at ordinary temperatures occurs in three allotropic forms (i) body-centered cubic form, alpha iron stable up to 910°C, (ii) face-centered cubic form, gamma iron occurring between 910 to 1,390°C, and (iii) body-centered delta iron allotrope forming above 1,390°C. Density 7.873 g/cm at 20°C melting point 1,538°C vaporizes at 2,861°C hardness (Brinell) 60 electrical resistivity 4.71 microhm-cm at 0°C tensile strength 30,000 psi Poisson s ratio 0.29 modulus of elasticity 28.5 X 10 psi thermal neutron absorption cross-section 2.62 bams velocity of sound 5,130 m/s at 20°C. 

Silvery-white metal close-packed hexagonal structure density 1.74 g/cm at 20°C, 1.57 g/cm3 at 650 C (hquid melt) melts at 650 C vaporizes at 1,090°C vapor pressure 5 torr at 678 C and 20 torr at 763 C electrical resistivity 4.46 microhm-cm at 20 C, 28.0 microhm-cm at 650 C (hquid melt) surface tension 563 dynes/cm at 681 C modulus of elasticity 6.5x10 Ib/sq in Poisson s ratio 0.35 thermal neutron absorption cross section 0.059 bam soluble in dilute acids. 

Silvery-white lustrous metal face-centered cubic crystal structure ductile ferromagnetic density 8.908 g/cm at 20°C hardness 3.8 Mohs melts at 1,455°C vaporizes at 2,730°C electrical resistivity 6.97 microhm-cm at 20°C total emissivity 0.045, 0.060 and 0.190 erg/s.cm2 at 25, 100 and 1,000°C, respectively modulus of elasticity (tension) 206.0x10 MPa, modulus of elasticity (shear) 73.6x10 MPa Poisson s ratio 0.30 thermal neutron cross section (for neutron velocity of 2,200 m/s) absorption 4.5 barns, reaction cross section 17.5 barns insoluble in water dissolves in dilute nitric acid shghtly soluble in dilute HCl and H2SO4 insoluble in ammonia solution. Thermochemical Properties... 

Silvery metal body-centered cubic structure imparts crimson-red color to flame density 0.862g/cm3 at 20°C melts at 63.25°C density of hquid potassium at 100°C is 0.819 g/cm and 0.771g/cm3 at 300°C vaporizes at 760°C vapor pressure 123 torr at 587°C electrical resistivity 6.1 microhm-cm at 0°C and 15.31 microhm-cm at 100°C viscosity 0.25 centipoise at 250°C surface tension 86 dynes/cm at 100°C thermal neutron absorption cross section 2.07 barns reacts violently with water and acids reacts with alcohol dissolves in liquid ammonia and mercury... 

Metallic appearance in massive form, black to metallic color in powdered state or in electrodeposited form hexagonal crystal system density 20.53 g/cm3 hardness (Brinell) 250 melts at 3,180°C vaporizes at 5,627°C (estimated) vapor pressure 4.6x10- torr at 2,500°C electrical resistivity 19.14 microhm -cm modulus of elasticity 67x10 psi at 20°C specific magnetic susceptibility 0.369x10 thermal neutron absorption cross section 86 barns/atom superconductivity transition temperature 1.7°K insoluble in water and hydrochloric acid soluble in dilute nitric acid and hydrogen peroxide slightly soluble in sulfuric acid. 

Silvery-white metal body-centered cubic crystals ductile soft and very hght (the fourth lightest metaUic element) Mobs hardness 0.3 density 1.522 g/cm3 at 18°C melts at 39.3°C density of the liquid metal 1.472 g/mL at 39°C vaporizes at 689°C producing a blue vapor vapor pressure 1 torr at 294°C and 10 torr at 387°C electrical resistivity 11.6 microhm-cm at 0°C and 13.1 mirohm-cm at 25°C viscosity 0.484 centipoise at 100°C magnetic susceptibility 0.09x10 cgs units at 18°C thermal neutron absorption cross section 0.73 barns reacts violently with water... 

Hard silvery-white metal hexagonal close-packed crystal structure density 12.41 g/cm3 at 20°C melts at 2,334°C vaporizes at 4,150°C electrical resistivity 7.1 microhm-cm at 0°C hardness (annealed) 200-350 Vickers units Young s modulus 3.0x10 tons/in magnetic susceptibility 0.427 cm /g thermal neutron absorption cross section 2.6 barns insoluble in water, cold or hot acids, and aqua regia can be brought into aqueous phase by fusion of finely divided metal with alkaline hydroxides, peroxides, carbonates and cyanides. 

Hard yellow metal exhibits two crystals forms an alpha form having a rhombohedral crystal structure at ordinary temperatures the alpha form converts to a body-centered cubic beta form at 917°C density 7.52 g/cm (alpha form) and 7.40 g/cm (beta form) melts at 1,074°C vaporizes at 1,791°C ignites in air at 150°C electrical resistivity 94 microhm-cm at 25°C thermal neutron absorption cross section 5,600 barns insoluble in water soluble in acid. 

Silvery white metal soft and hght turns shghtly yeUow when exposed to air density 2.99 g/cm exhibits two aUotropic modifications a hexagonal close-packed structure stable up to 1,335° transforms to body-centered cubic form above 1,335°C, having a density 3.19 g/cm melts at 1,541°C vaporizes at 2,831°C electrical resistivity 56.2x10 ohm-cm thermal neutron absorption cross section 24 1 bams decomposes in water. 

White metal with brdhant metaUic luster face-centered cubic crystals density 10.43 g/cm at 20°C, and 9.18 g/cm at 1,100°C melts at 961.8°C vaporizes at 2,162°C vapor pressure 5 torr at 1,500° C pure metal has the highest electrical and thermal conductive of aU metals, electrical resistivity of pure metal at 25°C 1.617x10 ohm-cm elastic modulus 71GPa (10.3x10 psi) Poisson s ratio 0.39 (hard drawn), 0.37 (annealed) viscosity of hquid silver 3.97 centipoise at 1,043°C thermal neutron absorption cross section 63 1 barns insoluble in water inert to most acids attacked by dilute HNO3 and concentrated H2SO4 soluble in fused caustic soda or caustic potash in the presence of air. 

Silvery-white metal when freshly cut rapidly turns yellow on exposure to air forming a thin oxide coating face-centered cubic structure malleable, ductile, and somewhat softer than calcium density 2.64 g/cm melts at 777°C vaporizes at 1,382°C vapor pressure 5 torr at 847°C and 20 torr at 953°C electrical resistivity 23 microhm-cm at 20°C thermal neutron absorption cross section 1.21 barns reacts with water soluble in ethanol. Thermochemical Properties... 

Silvery-gray metal slowly tarnishes in moist air crystallizes in hexagonal close-packed structure density 11.49 g/cm (calculated) melts at 2,172°C vaporizes at 4,265°C Young s (elastic) modulus 3.76 x 10 kg/cm Poisson s ratio 0.293 thermal neutron absorption cross-section 22 barns superconductor below 11°K insoluble in water and hydrochloric acid dissolves in nitric acid, concentrated sulfuric acid and aqua regia. 

Silvery-white lustrous metal when pure or dark gray amorphous powder orthorhombic crystals hardness 2.3 Mohs density 6.25 g/cm melts at 452°C vaporizes at 990°C modulus of elasticity 6.0x10 psi thermal neutron absorption cross section 4.7 0.1 barns insoluble in water, carbon disulfide, and benzene also insoluble in HCl soluble in sulfuric acid, nitric acid, and aqua regia also soluble in caustic potash and in solutions of alkali metal cyanides. 

Silvery-gray metal hexagonal crystal structure malleable, ductile, and soft enough to be cut with a knife density 8.223 g/cm melts at 1,359°C vaporizes at 3,221°C resistivity llhxlCH ohm-cm at 25°C Young s modulus 5.75xl0n dynes/cm2 (from velocity of sound measurements) shear modulus 2.28 dynes/cm2 Poisson s ratio 0.261 thermal neutron absorption cross section, 46 barns insoluble in water soluble in acids. 

---