Thermal neutron cross section

Niobium is also important in nonferrous metallurgy. Addition of niobium to tirconium reduces the corrosion resistance somewhat but increases the mechanical strength. Because niobium has a low thermal-neutron cross section, it can be alloyed with tirconium for use in the cladding of nuclear fuel rods. A Zr—l%Nb [11107-78-1] alloy has been used as primary cladding in the countries of the former USSR and in Canada. A Zr—2.5 wt % Nb alloy has been used to replace Zircaloy-2 as the cladding in Candu-PHW (pressurized hot water) reactors and has resulted in a 20% reduction in wall thickness of cladding (63) (see Nuclear reactors). 

Boron-10 has a natural abundance of 19.61 atomic % and a thermal neutron cross section of 3.837 x 10 m (3837 bams) as compared to the cross section of 5 x 10 m (0.005 bams). Boron-10 is used at 40—95 atomic % in safety devices and control rods of nuclear reactors. Its use is also intended for breeder-reactor control rods. 

Account must be taken in design and operation of the requirements for the production and consumption of xenon-135 [14995-12-17, Xe, the daughter of iodine-135 [14834-68-5] Xenon-135 has an enormous thermal neutron cross section, around 2.7 x 10 cm (2.7 x 10 bams). Its reactivity effect is constant when a reactor is operating steadily, but if the reactor shuts down and the neutron flux is reduced, xenon-135 builds up and may prevent immediate restart of the reactor. 

Metal A lomic number Atomic weight Lattice structure Density at 20°C (g/em ) Melting point (°C) Thermal conductivity at 0-l00°C (W/m°C) Specific heat at 0°C (J/kg C) Coefficient of linear expansion at 20-iOO°C X 70 Thermal neutron cross-section (barns) (10-- m ) Resistivity at 0°C (fiil em) Temperature coefficient of resistance o-ioo°c X 10 ... 

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. 

Soft, lustrous metal silver-like appearance close-packed hexagonal crystal system density 8.78 g/cm paramagnetic magnetic moment 11.2 Bohr magnetons melts at 1,472°C vaporizes at 2,694°C electrical resistivity 195 microhm-cm at 25°C Young s modulus 6.71xl0n dynes/cm2 Poisson s ratio 0.255 thermal neutron cross section 64 barns insoluble in water soluble in acids (with reactions). 

Silvery white metal soft and malleable hexagonal closed pack crystal system transforms to face-centered cubic crystals at 310°C which further transforms to a body-centered cubic allotropic modification at 868°C density 6.166 g/cm3 Brinnel hardness (as cast) 37 melts at 918°C vaporizes at 3,464°C vapor pressure 1 torr at 2,192°C electrical resistivity 56.8 x 10 ohm-cm at 25°C Young s modulus 3.84 x lO- dynes/cm Poisson s ratio 0.288 thermal neutron cross section 8.9 bams. 

Silvery-white metal hexagonal close-packed structure density 9.84 g/cm melts at 1,663°C vaporizes at 3,402°C electrical resistivity 59 microhm-cm slightly paramagnetic thermal neutron cross section 108 barns soluble in acids. 

Silvery-white, soft maUeable metal exists in two aUotropic forms an alpha hexagonal from and a beta form that has body-centered cubic crystal structure the alpha allotrope converts to beta modification at 868°C paramagnetic density 7.004 g/cm compressibility 3.0x10 cm /kg melts at 1024°C vaporizes at 3027°C vapor pressure 400 torr at 2870°C electrical resistivity 65x10 ohm-cm (as measured on polycrystalline wire at 25°C) Young s modulus 3.79xl0 ii dynes/cm2 Poisson s ratio 0.306 thermal neutron cross section 46 barns. 

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-white metal face-centered cubic crystalline structure density 12.02 g/cm Vickers hardness, annealed 37-39 melts at 1,554°C vaporizes at 2,970°C electrical resistivity 9.93 microhm-cm at 0°C Poisson s ratio 0.39 magnetic susceptibility 5.231x10 cm /g thermal neutron cross section 8... 

Silvery-white lustrous metal remains bright at all temperatures face-centered cubic crystal density 21.5g/cm3 Vickers hardness, annealed 38-40 melts at 1,768.4°C vaporizes at 3,825°C vapor pressure at melting point 0.00014 torr electrical resistivity 9.85 microhm-cm at 0°C magnetic susceptibility 9.0x10— cm /g Poisson s ratio 0.39 thermal neutron cross section 8 barns insoluble in water and acids soluble in aqua regia... 

Xenon occurs in the atmosphere at trace concentrations. It also occurs in gases from certain mineral springs. Xenon also is a fission product of uranium, plutonium, and thorium isotopes induced by neutron bombardment. The radioactive fission product, xenon-135, has a very high thermal neutron cross-section. The element has been detected in Mars atmosphere. 

The Physical Properties are listed next. Under this loose term a wide range of properties, including mechanical, electrical and magnetic properties of elements are presented. Such properties include color, odor, taste, refractive index, crystal structure, allotropic forms (if any), hardness, density, melting point, boiling point, vapor pressure, critical constants (temperature, pressure and vol-ume/density), electrical resistivity, viscosity, surface tension. Young s modulus, shear modulus, Poisson s ratio, magnetic susceptibility and the thermal neutron cross section data for many elements. Also, solubilities in water, acids, alkalies, and salt solutions (in certain cases) are presented in this section. 

ELEMENT TARGET ISOTOPE ISOTOPIC ABUNDANCE (%) PRODUCT NUCLIDE HALF- LIFE THERMAL NEUTRON CROSS SECTION BEST y FOR MEASUREMENT (KEV) NUMBER OFy s PER 1000 DECAYS ASSOCIATED y -RAYS KEV MEASUREMENT POSSIBLE INTERFERING NUCLEAR REACTIONS PRODUCING NUCLIDES OF INTEREST... 

Isotope mass number Abundance, % Thermal neutron cross section, m2 x 10 28 Contribution to the total cross section... 

Fluorocarbons, such as Viton, degrade the radiation stability of a proplnt compd, even though they have good thermal stability. The composite proplnts containing K perchlorate had high temp stability, but this applicability was limited by relatively poor radiation stability, as shown in Fig 22, due primarily to the high thermal-neutron cross section of chlorine (33.6 bams)... 

Mass No of Collisions Thermal Neutron Cross-sections, cm ... 

The density and thermal neutron cross-section values in Table 6 pertain to the thermal neutron attenuation gauging process. In this method, advantage is taken of the large thermal neutron scattering cross-section of hydrogen as compared to most other elements. In its simplest form, when a beam of thermal neutrons of intensity IQ traverses a sample of thickness x, the intensity 1 of neutrons measured by a thermal neutron detector will be... 

In neutron irradiation, the yield of 13<5Xe may be significantly enhanced due to neutron capture on 135Xe (isobaric yield 6.5%, half-life 9hr, thermal neutron cross section 3.6 x 106 bams). 

Element % Abundance Thermal Neutron Cross Section, barns Product Nuclide Half-Life Principal 7-photopeak, MeV... 

T nterest in the separation of isotopes started as a scientific curiosity. The question arose as to whether it was indeed at all feasible or possible to separate isotopes. After this question was answered in the affirmative (24), it became of interest to separate isotopes on a laboratory scale for use in scientific research. A few examples show the range of utility of separated isotopes. Deuterium has attained widespread use as a biochemical and chemical tracer. It is now abundantly available and is used as freely as any cheap chemical reagent. He has opened up an entirely new field of research in low temperature physics and has important applications in the production of temperatures below 1°K. with a thermal neutron cross section of 4,000 barns, has found wide use in nuclear particle detectors—neutron proportional counters. still finds use as a tracer, but in recent years its most frequent use has been in electron spin and nuclear magnetic resonance spectroscopy. occupies a unique position as the only usable tracer for nitrogen. finds application as a... 

Separated isotopes have played an important role in the production of nuclear power and in the development of nuclear energy. The importance of separated isotopes in this field can be seen at once by considering the thermal neutron cross sections of those isotopes which have become important in the nuclear industry. A few of these are given in Table I. The very small neutron absorption cross section of deuterium, compared with protium, together with its excellent moderating power, has made heavy water a very important reactor moderator. has found wide-... 

Table I. Thermal Neutron Cross Sections of Some Isotopes Useful for Nuclear Energy Production...

C, high thermal neutron cross section (115 bams). Good corrosive resistance and high strength. 

At such low concentrations the lithium and boron are exposed homogenously to the neutron flux. Because of the large thermal-neutron cross sections for Ii and °B, these isotopes are depleted significantly during the typical fuel irradiation time of 4 years. Therefore, to calculate the tritium activity (iVX) - in a fuel element after an irradiation time, we rewrite Eq. (2.100), recognizing that the chain-linking term here is 0o instead of X. For the Li reaction of Eq. (8.47),... 

The separation of yttrium from the lanthanides is performed by selective oxidation, reduction, fractionated crystallization, or precipitation, ion-exchange and liquid-liquid extraction. Methods for determination include arc spectrography, flame photometry and atomic absorption spectrometry with the nitrous oxide acetylene flame. The latter method improved the detection limits of yttrium in the air, rocks and other components of the natural environment (Deuber and Heim 1991 Welz and Sperling 1999).Other analytical methods useful for sensitive monitoring of trace amounts of yttrium are X-ray emission spectroscopy, mass spectrometry and neutron activation analysis (NAA) the latter method utilizes the large thermal neutron cross-section of yttrium. For high-sensitivity analysis of yttrium, inductively coupled plasma atomic emission spectroscopy (ICP-AES) is especially recommended for solid samples, and inductively coupled plasma mass spectroscopy (ICP-MS) for liquid samples (Reiman and Caritat 1998). 

N.E. Holden, Review of Thermal Neutron Cross Sections and Isotopic Composition of the Elements, BNL-NCS-42224 (March 1989). 

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