Abundance relative

Many artificial (likely radioactive) isotopes can be created through nuclear reactions. Radioactive isotopes of iodine are used in medicine, while isotopes of plutonium are used in making atomic bombs. In many analytical applications, the ratio of occurrence of the isotopes is important. For example, it may be important to know the exact ratio of the abundances (relative amounts) of the isotopes 1, 2, and 3 in hydrogen. Such knowledge can be obtained through a mass spectrometric measurement of the isotope abundance ratio. 

For any one element, the abundances (relative amounts) of isotopes can be described in percentage terms. Thus, fluorine is monoisotopic viz., it contains only nuclei of atomic mass 19, and phosphorus has 100% abundance of atoms with atomic mass 31. For carbon, the first two isotopes occur in the proportions of 98.882 to 1.108. 

Scheme 12. Schematic structure of vinyl-eb-PDMS chains (dashed line) crosslinked with polymeric TMS-eb-PHMS through the hydrosilylation cure reaction. For illustration purpose the PDMS chains in this scheme are shorter and less abundant relative to PHMS than in real system.

Cations exchanged into the interlayers of expandable clays (smectites) are comparatively easy to study with NMR methods because the cations become major components of the phase and their concentrations are often several wt %. In addition to Cs Li, Na, K, and Cd have been studied by NMR. We have chosen to investigate Cs because it is a significant component of nuclear waste, because it provides an end-member case as the least electronegative cation, and because it has desirable nuclear properties (100% abundance, relatively high frequency, 65.5 MHz at H = 11.7 T, and small quadrupole moment)... 

Nucleus Natural abundance (%) Relative sensitivity Ease of use... 

Relative Abundance Relative Abundance Relative Abundance... 

While the -abundances relative to iron (i.e., <[(Si,Ca,Ti)/Fe]>) I derive for the most metal-poor cluster (NGC 5053) in Table 1 are 0.1 dex lower than those of other metal-poor clusters purported to be associated with the Sgr dSph (NGC 4147 and NGC 5634), the abundances are in good agreement with those of NGC 6535, a cluster born within the MWG. 

In addition to results from this study, Table 1 includes two of the relatively more metal-rich globular clusters associated with the Sgr dSph. There appears to be little in common between the two metallicity groups in their < a>-abundances relative to iron. Abundances reported so far for in situ Sgr dSph field stars of comparable metallicities [4] are in accord with those of its metal-rich clusters. 

The derived supernovae ratios of the metal-rich systems in Table 1 indicate that both the low-a and low iron-peak abundances are consistent with significant contributions from Type la supernovae. In general, when compared with the abundances of stars born within the MWG, the metal-rich stars associated with the Sgr dSph possess low iron-peak abundances relative to iron (e.g., [3], [4]). 

Table 1. Abundances relative to solar for our target stars in NGC 1904.

Fig. 1. Left panel. Post-explosive yields versus mass of the Ge isotopes for a 25 M of solar composition by [10]. Arrows represent a production factor of 200 over the initial mass fraction of each isotope. Right panel. Logaritmic abundances relative to O and to solar ratio observed in the DLA-B/FJ0812+32 System (dust corrected) [5]. The observed [Zn/O] value is represented by a full square.

Fig. 1. Evolution of 3He/H in the solar neighborhood, computed without extra-mixing (upper curve) and with extra-mixing in 90% or 100% of stars M < 2.5 M (lower curves). The two arrows indicate the present epoch (assuming a Galactic age of 13.7 Gyr) and the time of formation of the solar system 4.55 Gyr ago. Symbols and errorbars show the 3He/H value measured in meteorites (empty squares) Jupiter s atmosphere (errorbar) the local ionized ISM (filled triangle) the local neutral ISM (filled circle) the sample of simple Hll regions (empty circles). Data points have been slightly displaced for clarity. The He isotopic ratios has been converted into abundances relative to hydrogen assuming a universal ratio He/H= 0.1. See text for references.

H2C0, HCN, HC0+, HCC, C3N, C4H. The high density and temperature of black interstellar clouds facilitates a richer chemistry in which molecules such as dimethyl ether and ethyl alcohol are formed [1]. Figure 1 summarizes the carbon compounds which have been found in interstellar space and their abundances relative to hydrogen. Note that the carbon compounds decrease in abundance with increasing complexity. 

Table 3.4. Solar abundances relative to log N = 12.00 meteoritic abundances...

Stellar compositions are traditionally discussed in terms of abundances relative to iron, X/Fe (where X is the relevant element), as a function of the ratio of iron to hydrogen, Fe/H, this being the most convenient arrangement for observational purposes. 

Nuclide Spin I Electric quadmpole moment eQ (10-2 m2) Natural abundance (%) Relative sensitivity Gyromagnetic ratio y (103 radT- S-l)a NMR frequency (MHz) Bo = 2.3488 T)3... 

Aluminum-26 is produced by stellar nucleosynthesis in a wide variety of stellar sites. Its abundance relative to other short-lived nuclides provides information about the stellar source(s) for short-lived nuclides and the environment in which the Sun formed. Aluminum-26 is also produced by interactions between heavier nuclei such as silicon atoms and cosmic rays. Aluminum-26 is one of several nuclides used to estimate the cosmic-ray exposure ages of meteorites as they traveled from their parent asteroids to the solar system. 

Isotope Spin Natural abundance Relative sensitivity NMR frequency in a field of 2.3488 T Electric quadrupole moment Q (in multiples of e x 10 24 cm2)... 

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