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Physics for medical imaging
Published in Ken Holmes, Marcus Elkington, Phil Harris, Clark's Essential Physics in Imaging for Radiographers, 2021
A good example of an atom with a number of isotopes is carbon, which has a total of 15 known isotopes. Carbon 12 is by far the commonest accounting for over 99% of all the carbon on earth. Three other well known isotopes of carbon are carbon 11, carbon 13 and carbon 14. These and other isotopes of carbon are unstable and undergo radioactive decay.
Measurement of Pressure
Published in Pramod K. Naik, Vacuum, 2018
The carbon value is considered 12.0000, as all the other masses are measured on the carbon-12 scale which is based on the carbon-12 isotope having a mass of exactly 12. A typical mass spectrum is shown in Fig. 5.28. The main residual gases in this vacuum system are hydrogen, water, carbon monoxide and some carbon dioxide. It is important to note that the criterion for some test gas molecules to pass the mass spectrometer is the right e/m and not simply m. This means that doubly-charged ions appear as particles with half the mass in the spectrum. CO does for example not only give a peak at m = 28 but also one at m = 14 due to double ionization. The gases are also dissociated in the spectrometer such that one does not only find one peak for single-ionized water at m = 18 but also peaks at m = 16, 17 and 2 for the fragments. Without any bakeout, the pressure of the system will be dominated by a high partial pressure of water. After the bakeout of the system, this will be significantly reduced and the total pressure will be determined by CO and hydrogen. If there is an air leak in the system this would show up as peaks of 28 (N 2) and 32 (O 2). The peak at 28 is always present due to CO and a small peak of 32 might even be present in a leak-tight chamber. However, more conclusions can be drawn from the cracked fragments if the peak at 14 (N) is bigger than the peak at 12 (C), this is usually an indication of an air leak.
Elements, Isotopes, and Their Properties
Published in Robert E. Masterson, Nuclear Engineering Fundamentals, 2017
The answer to this question lies in the fact that about two-thirds of the naturally occurring have more than one isotope,* and the atomic weights in the periodic table simply represent the measured average of the atomic weights of these isotopes. For example, carbon has three naturally occurring isotopes—Carbon-12, Carbon-13, and Carbon-14, and each of these isotopes occurs in nature in slightly different amounts. Hence, the weight for the element carbon that appears in the periodic table is the average of the atomic weight of these three isotopes—adjusted for the relative amounts of each isotope that are present. Atomic weights of this type are also called fractional atomic weights because they are not whole numbers as the simple chemical formula A = Z + N might suggest. In the case of the element carbon, there is a naturally occurring isotope called carbon 14 that can be used to date bones and even human tissue. This isotope is used in radio-carbon dating to determine the ages of animals and plants that died a long time ago. It has a very short half-life (of about 25,000 years), and hence it decays very rapidly. Thus, although the element carbon appears to be stable, not all of it on the Earth is “stable” per se. The amount of Carbon-14 that is produced in the upper atmosphere must therefore be taken into account when determining the atomic weight of carbon in the periodic table.
Cascade production of secondary electrons and photons and energy absorption mechanisms in liquid nitrogen irradiated by photons in the energy range of 0.027–17.4 keV
Published in Radiation Effects and Defects in Solids, 2023
Alexander P. Chaynikov, Andrei G. Kochur, Victor A. Yavna
Similar results were obtained earlier for solid neon (11), amorphous carbon (12), and liquid water (13). Table 3 shows calculated portions of energy absorption in LN2 through different channels averaged over the whole incident photon energy interval in comparison with respective values for solid neon, amorphous carbon and liquid water. In all cases the principal transmitters of energy to medium are high-energy secondary electrons (bel). Second-largest contribution is from low-energy secondary photons (cphot). This contribution is maximal in water which, as discussed in (13), is explained by the presence of a large number of hydrogen atoms emitting secondary photons mostly in the LE range. Another peculiarity is extremely low contribution of HE photons in the case of amorphous carbon. Analysis of the decay trees showed that this difference is due to the fact that in carbon, 2p–2s photon emitted in the decay of the 2s vacancy is unable to ionize the 2p subshell.
Optimization of the adsorption process in the treatment of sanitary landfill leachate by Fenton-adsorption
Published in Chemical Engineering Communications, 2023
Roger I. Méndez-Novelo, Liliana San-Pedro, Armin A. May-Marrufo, Emanuel Hernandez-Núñez, Caridad Vales-Pinzón, Mauricio A. Escalante Soberanis
Granular coconut activated carbon 12 × 40 obtained better efficiencies in the adsorption process of Fenton-treated leachates at the laboratory level. However, in the adsorption column, it had poor performance. The maximum removal efficiency in the adsorption column was 87% for COD and 99% for color. Conversely, the Gama L 8 × 30 carbon exhibited better removals reaching >99% for COD and color in the column test. This was since Gama L carbon has a greater amount of mesopores compared to the carbons tested in this study, this characteristic allows it to better adsorb the molecules previously degraded in the Fenton process. Based on these results it is recommended to use Gama L carbon for the adsorption process in the treatment of landfill leachates with Fenton-adsorption. According to the results, it is concluded that the Freundlich isotherm explains in a great way the adsorption with Gama L (96%), while the Temkin model fits better to the behavior of granular coconut (80%) and that in both cases the adsorption is in multilayer (physisorption).
Insight Into Surface Texture-Induced Dual Effects on Friction of WC-Co Dry Sliding Against Continuous Carbon Fiber-Reinforced Thermoplastic and Thermosetting Composites
Published in Tribology Transactions, 2022
Xin Dong, Chaoyang Dong, Bo Wu
Especially, the high-magnification SEM image of the tribofilms’ tail (region B in Fig. 4b1) is displayed in Fig. 4b3. Parts of the tribofilms on the left region were discrete, irregular, and uneven. The boundary between the tribofilms and the WC-Co substrate was impossible to discern with accuracy, suggesting that the transition from the substrate to the tribofilms was continuous. Furthermore, the EDS signal of carbon element became significant (spot 2, Fig. 4b5) instead of weak (spot 1, Fig. 4b4), and an oxygen element was detected in spot 2 compared with spot 1. Elemental mapping analyses of Fig. 4b3 further show that the signal intensity of the carbon element in the region coated with tribofilms was much stronger than that in the region without tribofilms (Fig. 4b6). Considering EDS cannot detect the hydrogen element (38), pristine PEEK contains 86.3 at% of carbon atoms (The chemical formula of PEEK contains 19 carbon, 12 hydrogen, and 3 oxygen atoms (39)). It is convincing that these tribofilms chemically originated from the CCF-PEEK pin and were transferred from the pin to the textured WC-Co substrate because of the elevated carbon signal and the discovery of the oxygen element on the tribofilm-coated surface. In other words, line texture facilitated the adhesion of the CCF-PEEK transfer film, which contained CF-related materials (Fig. 4b1) (19), onto the WC-Co surface.