Isotopes, 69-70, Table

RELATIVE ABUNDANCES OF NATURALLY OCCURRING ISOTOPES Table 4.18 Relative Abundances of Naturally Occurring Isotopes... 

Atoms with the same value of Zbut different values of A are isotopes (Table 11.1). Many isotopes are stable but others are naturally or artificially radioactive, i.e. their atomic nuclei disintegrate, emitting particles or radiation. This changes the nuclear structure of the atom and often results in the production of a different element. 

Because isotopes of the same element have the same number of protons and the same number of electrons, they have essentially the same chemical and physical properties. However, the mass differences between isotopes of hydrogen are comparable to the masses themselves, leading to noticeable differences in some physical properties and slight variations in some of their chemical properties. Hydrogen has three isotopes (Table B.2). The most common ( H) has no neutrons so its nucleus is a lone proton. The other two isotopes are less common but nevertheless so important in chemistry and nuclear physics that they are given special names and symbols. One isotope (2H) is called deuterium (D) and the other ( H) is called tritium (T). 

If only one counter can be purchased, then a gamma counter is the instrument of choice since most assays are now performed with gamma emitting isotopes. Table I lists the isotopes in common usage for competitive protein binding assays. 

There are ten, naturally occurring isotopes of tin and some artificial isotopes have been synthesized in cyclotrons and nuclear reactors. The naturally occurring tin isotopes range in mass from 112 to 124. The natural abundance (percentage of each isotope) also varies widely. For example, tin-115 accounts for only 0.35% while tin-120, the most abundant of the naturally occurring tin isotopes, accounts for almost 35% of the tin isotopes (Table 5)32. 

Cosmic abundances of elements and isotopes Table 3.3. Exponential curves of growth... 

The isotopic mass is the exact mass of an isotope. It is very close to but not equal to the nominal mass of the isotope (Table 3.1). The only exception is the carbon isotope which has an isotopic mass of 12.000000 u. The unified atomic mass... 

The quantities FA and FB are the apparent abundances of the sample for A- and B-type atoms, respectively. These are what an atom-probe analysis gives directly. To find the true abundances, fA and/B, one may solve eqs (3.21) to (3.24) for them using a numerical method. For this purpose, it is necessary that the value of en is known. This quantity can be derived by comparing the measured relative abundance of two isotopes of the same element with that listed in the isotope table. There are a few asymptotic behaviors of interest ... 

Along with the abundances of the isotopes, Table 4.2 also provides information on the processes that synthesized the isotopes. The processes are listed in order of importance, with minor processes shown in lower case. Note that most isotopes are produced by more than one process, and that isotopes of elements heavier than iron are produced predominantly by the s- and r-processes. / -process isotopes invariably have quite low abundances. 

The solar system formed from a well-mixed collection of gas and dust inherited from its parent molecular cloud. The bulk composition of this material, as best we can know it, is given by the solar system abundances of elements and isotopes (Tables 4.1 and 4.2). From this bulk material, the planets, asteroids, and comets formed, each with its own unique composition. The processes that produced these compositions separated, or fractionated, elements and isotopes from one another. By studying these elemental and isotopic fractionations, we can potentially identify the processes that separated the elements and can leam about the physical conditions involved. This is particularly important for understanding the early solar system, because its processes and conditions are not directly observable. 

Strontium has four naturally occurring isotopes (Table 4.2). It is a member of the alkaline earths (Group 2A) along with beryllium, magnesium, calcium, barium, and radium (Fig. 2.4). Strontium substitutes for calcium and is abundant in minerals such as plagioclase, apatite, and calcium carbonate. 

Rhenium has two naturally occurring isotopes (Table 4.2), one of which, 187Re, (3-decays... 

Isobutane, dipole moment of, 225 Isomorphic groups, 392 Isotopes, table of properties of, 470 Isotopic substitution in ESR, 379 in IR spectroscopy, 244 in microwave spectroscopy, 221-223 in NMR, 354-355... 

Physical Properties. Hafnium is a hard, heavy, somewhat ductile metal having an appearance slightly darker than that of stainless steel. The color of hafnium sponge metal is a dull powder gray. Physical properties of hafnium are summarized in Table 1. These data are for commercially pure hafnium which may contain from 0.2 to 3% zirconium. Although a number of radioactive isotopes have been artificially produced, naturally occurring hafnium consists of six stable isotopes (Table 2). Hafnium crystallizes in a body-centered cubic system which transforms to a hexagonal close-packed system below 2033 K. 

N-H coupling constants have been determined on a sample of thiazole enriched in this isotope (Table 10). 

Several steroids with an organyltelluro group bonded to the 3- or 19-position or to the alkyl chain at the 17-position of the steroid nucleus have been prepared and tested as imaging agents for the adrenal gland using radiation from the l23mTe isotope (Table 11 p.395). 

Stable Isotope Techniques. Although the availability of radioiron isotopes has facilitated our understanding of iron nutrition, their utilization is becoming restricted for safety and ethical reasons, especially when infants, children, and women are involved. The availability of enriched stable iron isotopes (Table I) and methodologies for quantifying them make stable isotopes a feasible alternative to radioisotopes as biological tracers. Neutron activation analysis and mass spectrometry are currently available to nutritionists for quantifying stable isotopes of minerals. 

Because of the occurrence of 13c, and 1 0, and because mass spectrometry sorts ions according to m/e values, the peak intensities at m/e 252-256 do not represent the true proportion of iron isotopes. Table II is an example of how the abundances of the diligand ions deviate from the abxmdeuices of iron isotopes. Theoretically, the abundances of the diligand species can be calculated from the abundances of iron isotopes (IJ ). Calculated values may be used as a reference for the accuracy of the experimental values. 

The use of °Th and Pa in determining the chronology of deep-sea sediments is based on their production in the oceanic water column from the decay of uranium isotopes (Table 1) dissolved in seawater and their incorporation in the bottom deposit by strong adsorption on particle surfaces followed by the sedimentation of the particles. This combination of the processes leading to removal of particle-reactive radionuchdes such as these from the water column is referred to as chemical scavenging (see Chapter 6.09). At the time of deposition, sediment contains an initial quantity Nq of excess (unsupported) °Th or Pa activity along with small quantities supported by decay of the parent uranium isotopes that are present. The decay of the excess nuclides with time and their burial is governed by Equation (1) and leads to an exponential decrease of the unsupported component as a function of the depth in the sediment. 

Although the formalism for X-ray and neutron diffraction is essentially the same, it is appropriate to treat them separately because of the nature of the basic interaction. For the case of neutron diffraction, neutrons are scattered isotropically by all the nuclei of the system. The degree to which this takes place is determined by the coherent neutron scattering length b, which varies from isotope to isotope (Table I). Because the scattering is isotropic, the results of a given experiment can readily be presented in terms of a total radial distribution function. 

The sensitivity gain of proton detected Heteronuclear Multiple-Quantum Coherences (HMQ.C) experiments, as compared with direct heteronuclear detected ones and with polarization transfer techniques like INEPT [22-24] using heteronuclear detection, can be calculated [27,28] for the Sn, Sn and Sn isotopes (Table 3). 

Because most elements consist of a mixture of stable isotopes (Table 2.3), isotope peaks are observed in mass spectra. For a given elemental composition, the isotope pattern can be predicted using a computer program. The equidistant peaks in an isotope pattern, i.e., at one m/z unit for a single-charge ion, represent a series of ions with relative abundances, that should closely agree with the theoretically predicted values. 

Selected properties of the element are shown in Table 1.1.1. It is in Group 14 of the Periodic Table, with the electronic configuration [Kr] 4d ° 5s 5p its principal valence state is Sn(IV), though Sn(II) inorganic compounds are common, and many stannous organic compounds, with specially designed structures, have been prepared in recent years. Tin has 10 stable isotopes (Table 1.1.2), which is the largest number for any element, and results in very characteristic mass spectra. The " Sn and Sn isotopes, each with spin 1/2, are used in NMR spectroscopy. The y-active " Sn isotope, which is prepared by the neutron-irradiation of enriched Sn, is used in Mossbauer spectroscopy. 

In practice, it is important to be able to restrict the type and number of elements in any possible formula so as to improve the degree of confidence in selecting the most appropriate formula and to eliminate impossible or unlikely combinations of elements. Further information to help with this may be gleaned from an examination of the isotope pattern of the molecular ion. Most of the elements present in organic compounds (C, H, N, O, P, and S Si must obviously be included if silyl derivatives were used for GC/MS) have two or more stable isotopes (Table 7). This information can be used, for example, to estimate the number of carbons present in an... 

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