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Introduction
Published in Armen S. Casparian, Gergely Sirokman, Ann O. Omollo, Rapid Review of Chemistry for the Life Sciences and Engineering, 2021
Armen S. Casparian, Gergely Sirokman, Ann O. Omollo
The atomic masses are given for each element in the periodic table in amus or atomic mass units. The mass number of a given isotope of an element is the sum of the number of protons and the number of neutrons in its nucleus. Recall that in Example 1.1, the mass numbers of the three isotopes of uranium were given as U-234, U-235, and U-238. However, this is not equivalent to the atomic weight. Most elements have more than one isotope, so the natural distribution of the isotopes of an element must also be taken into consideration. Using the carbon-12 isotope as the standard for mass, atomic masses can then be assigned to all the elements. For each element, this number must be a number that is averaged over all of its isotopes according to their relative percent natural abundance. The atomic weight of an element, then, is the average atomic mass of all of the element’s naturally occurring isotopes. The molecular mass then becomes the sum of the atomic weights comprising the molecule, according to the number of each kind of atom occurring in the molecule. In other words, the molecular mass is the sum of the weights of the atoms represented in a molecular formula. Molecular masses (also called molecular weights) are the masses of molecules, which consist of essentially covalent compounds, while formula masses (also called formula weights) are the masses of formula units, which are essentially ionic compounds. The unit, in either case, is the amu, but often converted to the more useful grams/mole, which has the same numerical value.
Physics for medical imaging
Published in Ken Holmes, Marcus Elkington, Phil Harris, Clark's Essential Physics in Imaging for Radiographers, 2021
The mass number is the total number of protons and neutrons that form the nucleus. As electrons have negligible weight they are not included in the mass number. The commonest form of carbon consists of 6 protons and 6 neutrons and therefore has a mass number of 12. This natural form of carbon is referred to as ‘carbon 12’.
Introduction to Nanosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
The number of protons in the nucleus of an atom of an element is its atomic number (Z). The total number of protons and neutrons in the nucleus of an atom gives its mass number, atomic weight (A), or relative atomic mass. It is the ratio of the average mass per atom of the naturally occurring form of an element to 1/12th the mass of a carbon-12 isotope; an isotope is one or more atoms of an element having the same atomic number but a different atomic weight. One-twelfth the mass of a carbon-12 atom is called the atomic mass unit (amu) and is = 1.66033 × 10−27 kg.
Influence of Particle Beam and Accelerator Type on ADS Efficiency
Published in Nuclear Science and Engineering, 2023
M. Paraipan, V. M. Javadova, S. I. Tyutyunnikov
The energy efficiency and Pnet were analyzed for two situations: when the beams are accelerated in a linac and when the beams are accelerated in a cyclotron. In both cases, the beam intensity was the same, and a proton was considered as the reference particle. In linacs, Pacc is proportional to the accelerator length and scales with the ratio A‧E/Z, and in cyclotrons, it is proportional to the area of the accelerator and scales as (A‧p/Z)2. Here, A is mass number, Z is atomic number, E is energy per nucleon, and p is momentum per nucleon. This approach allows one to calculate Pspent necessary to accelerate a given beam if one knows accelerator efficiency η0 for a reference particle with atomic number Z0, mass number A0, and final energy per nucleon E0 (momentum per nucleon p0).
Comprehensive simulation study on CT isotope imaging beyond the experiment on the 208Pb based on nuclear resonance fluorescence
Published in Journal of Nuclear Science and Technology, 2021
Hani Negm, Heishun Zen, Hideaki Ohgaki
represents the atomic attenuation along the beam-axis, while stands for the nuclear attenuation of NRF. L is the distance from the source to the transmission detector. denotes the effective mass number through the beam axis, the atomic mass of the IOI, the Avogadro’s number. is the atomic cross-section due to EM-process, k, e.g. Compton scattering, photoelectric effect, etc., while is the cross-section of the NRF transition line j of the ith isotope. On the other hand, when the IOI is off the beam-axis, the transmission factor of the off-resonance (), , can be expressed by:
New infrared spectra of CO2–Xe: modelling Xe isotope effects, intermolecular bend and stretch, and symmetry breaking of the CO2 bend
Published in Molecular Physics, 2021
A. J. Barclay, A. R. W. McKellar, Colin M. Western, N. Moazzen-Ahmadi
Using these scaling factors, we tried fitting the 27 observed microwave transitions [3] of CO2-129Xe, -131Xe, -132Xe, and -134Xe (with hyperfine splitting removed for 131Xe) in a unified fashion using a single value for B and C, with scaling, rather than individual values for each isotope. This gave good results, but there was still some remaining systematic dependence on xenon mass. This dependence was minimised by introducing new empirical parameters Badj and Cadj which act as slight corrections to the rigid model scaling factors. The B and C rotational parameters are then given by where N is the xenon atomic mass number (129, 130, etc.), N0 is a ‘standard' atomic mass number (taken to be 131, closest to the weighted average atomic mass), and FB and FC are the rigid model scaling factors relative to 131Xe, as listed in Table 1. For simplicity, we use atomic mass number here rather than the actual atomic masses, but the difference is negligible in the present context.