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Basic Atomic and Nuclear Physics
Published in Douglas S. McGregor, J. Kenneth Shultis, Radiation Detection, 2020
Douglas S. McGregor, J. Kenneth Shultis
The relative atomic massA of any particular isotope, a dimensionless physical quantity, is the ratio of the mass of one atom of the isotope to 1/12 the mass of an atom of 12C. It is equivalent to the older term atomic weight.10
Molecular Kinetic Theory of Gases and Its Implications
Published in Igor Bello, Vacuum and Ultravacuum, 2017
Molar masses of gases and vapors are essential in the calculation of vacuum physical processes. The molar masses are numerically equal to the dimensionless relative atomic or molecular masses. The relative atomic mass of each chemical element is listed in the periodic table of chemical elements. For example, the relative atomic mass of helium is 4.0026. This dimensionless number numerically corresponds to the helium molar mass of 4.0026 kg/kmol or 4.0026 g/mol. Similarly, the relative atomic and molar masses of all gases in the eighth group of the periodic table are numerically equal. Since valence orbitals of these gases are entirely occupied by electrons, they are chemically inert and monatomic gases. Other gases, in their pure forms, occur in diatomic molecules. Therefore, the molecular relative masses are twice that of the atomic masses given in the periodic table. For instance, the relative atomic mass of nitrogen N is 14.0067 in the periodic table. Since nitrogen forms stable diatomic molecule N2, the relative molecular mass is 2 × 14.0067 = 28.0134, which corresponds to the nitrogen molar mass Ma = 28.0134 kg/kmol.
Symbols, Terminology, and Nomenclature
Published in W. M. Haynes, David R. Lide, Thomas J. Bruno, CRC Handbook of Chemistry and Physics, 2016
W. M. Haynes, David R. Lide, Thomas J. Bruno
susceptibility increases with temperature up to a critical value, the Néel temperature, above which the material becomes paramagnetic. Antiparticle - A particle having the same mass as a given elementary particle and a charge equal in magnitude but opposite in sign. Appearance potential* - The lowest energy which must be imparted to the parent molecule to cause it to produce a particular specified parent ion. This energy, usually stated in eV, may be imparted by electron impact, photon impact, or in other ways. More properly called appearance energy. [3] Appearance potential spectroscopy (APS) - See Techniques for Materials Characterization, page 12-1. Are (a) - A unit of area equal to 100 m2. [1] Arenes - Monocyclic and polycyclic aromatic hydrocarbons. See aromatic compounds. [5] Aromatic compounds - Compounds whose structure includes a cyclic delocalized -electron system. Historical use of the term implies a ring containing only carbon (e.g., benzene, naphthalene), but it is often generalized to include heterocyclic structures such as pyridine and thiophene. [5] Arrhenius equation - A key equation in chemical kinetics which expresses the rate constant k as k = Aexp(-Ea/RT), where Ea is the activation energy, R the molar gas constant, and T the temperature. A is called the preexponential factor and, for simple gas phase reactions, may be identified with the collision frequency. Arsines - AsH3 and compounds derived from it by substituting one, two or three hydrogen atoms by hydrocarbyl groups. RAsH2, R2AsH, R3As (R not equal to H) are called primary, secondary and tertiary arsines, respectively. [5] Aryl groups - Groups derived from arenes by removal of a hydrogen atom from a ring carbon atom. Groups similarly derived from heteroarenes are sometimes subsumed in this definition. [5] Astronomical unit (AU)* - The mean distance of the earth from the sun, equal to 1.49597870 × 1011 m. Atomic absorption spectroscopy (AAS) - See Techniques for Materials Characterization, page 12-1. Atomic emission spectroscopy (AES) - See Techniques for Materials Characterization, page 12-1. Atomic force microscopy (AFM) - See Techniques for Materials Characterization, page 12-1. Atomic mass* - The mass of a nuclide, normally expressed in unified atomic mass units (u). Atomic mass unit (u)* - A unit of mass used in atomic, molecular, and nuclear science, defined as the mass of one atom of 12C divided by 12. Its approximate value is 1.66054 × 10-27 kg. Also called the unified atomic mass unit. [1] Atomic number (Z) - A characteristic property of an element, equal to the number of protons in the nucleus. Atomic weight (Ar)* - The ratio of the average mass per atom of an element to 1/12 of the mass of nuclide 12C. An atomic weight can be defined for a sample of any given isotopic composition. The standard atomic weight refers to a sample of normal terrestrial isotopic composition. The term relative atomic mass is synonymous with atomic weight. [2] Attenuated total reflection (ATR) - See Techniques for Materials Characterization, page 12-1.
Adsorption properties of radionuclides on BC3: the first principles study
Published in Molecular Physics, 2022
Nan Zhou, Yong Qin, Jie Tan, Jinjuan Cheng, Shuaixing He, Hai Li, Xijun Wu
In the adsorption system, graphene and various nuclides form an equilibrium system. We calculated the equilibrium adsorption rate of nuclides on graphene. According to the statistical physical theory, the adsorption rate is shown in the following formula [39], In this formula, is the Boltzmann’s constant, and is the temperature of the circumstance. Where is the density of the nuclide in the system, is the Planck constant and is the relative atomic mass of nuclide atom. Finally, can be determined by the first-principles calculation, which is one result of our study.
Numerical and experimental evaluation of adhesion properties of asphalt-aggregate interfaces using molecular dynamics simulation and atomic force microscopy
Published in Road Materials and Pavement Design, 2021
Bingyan Cui, Xingyu Gu, Hao Wang, Dongliang Hu
The elemental analysis tests were performed through Elementar (Vario III) to measure the element content of hydrogen (H) and carbon (C) in asphalt binders. According to the ASTM D5291, the content of carbon and hydrogen in the asphalt sample can be determined. Firstly, the sample was combusted in an oxygen atmosphere at 950°C. The generated carbon and hydrogen oxides were separated from each other by adsorption over a high-resolution silica gel chromatography column. Then, carbon dioxide was brought into Thermal Conductivity Detector (TCD) by carrier gas for detection. Finally, the desorbed water was carried into TCD for detection. The error of the experiment was less than 0.3%. Based on their relative atomic mass, the hydrogen-to-carbon atom ratio (H/C) can be calculated. Higher H/C atom ratios indicate fewer aromatic rings in materials (Zhang et al., 2011). With aging in asphalt binders, the number of aromatic rings will increase. Therefore, results from element analysis tests will be used to validate the molecular structures of asphalt models.
Tuning phonon transport spectrum for better thermoelectric materials
Published in Science and Technology of Advanced Materials, 2019
Here, fi(α) and mi(α) are the mole fraction and relative atomic mass of the ith isotope of the α atom in unit cells, respectively. Equation (4) indicates that the scattering rates of high-frequency modes are moderate compared with Klemens model but they are still much higher than those of lower frequency modes. This model is widely used to predict the thermal conductivity of alloys, such as SixGe1−x [87], PbTexSe1−x [88], BixSb1−x [89], Mg2SixSn1−x [90], half-Heusler [91], PbxM1−xTe (M = Mg, Ca, Sr, Ba) [92] and even a phase transition material PbxGe1−xTe [93] combining phonon transport properties of the bulk crystals obtained by ALD calculation with first-principles interatomic force constants. In these works, virtual crystal approximation [94] is employed to evaluate intrinsic phonon properties such as τanh, where the mass and force field of the crystal are kept homogeneous but modulated to be the weighted average between the values of host and guest atoms or compounds. Note that this ‘ALD + Tamura’ model is rigorous for quantifying the effect of low-concentration isotopes on the thermal conductivity [95,96].