Isotopes percentage

TABLE 29.1. Forms of uranium and their respective isotope percentages... 

TABLE 33.1 Forms of Uranium and Their Respective Isotope Percentages... 

If this is multiplied by 100, it becomes atom%, a percentage that relates the proportion of heavy isotope to the sum of the heavy and light isotopes. 

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. 

Whether this is true or not, meteorites give us one definite piece of information. Isotopic analysis shows that each element in a meteorite has the same isotopes in the same percentages that this same element has on earth. The accepted explanation for this fact is that meteorites and the earth share a common origin and that they became separated after the elements were created. 

E.ll The molar mass of boron atoms in a natural sample is 10.81 g-mol-1. The sample is known to consist of 10B (molar mass 10.013 g-mol ) and UB (molar mass 1 1.093 g-mol 1). What are the percentage abundances of the two isotopes ... 

A few elements, among them fluorine and phosphoras, occur naturally with just one isotope, but most elements are isotopic mixtures. For example, element number 22 is titanium (Ti), a light and strong metal used in Jet engines and in artificial human Joints. There are five naturally occurring isotopes of Ti. Each one has 22 protons in its nuclei, but the number of neutrons varies from 24 to 28. In a chemical reaction, all isotopes of an element behave nearly identically. This means that the isotopic composition of an element remains essentially constant. The isotopic composition of Ti (number percentages) is... 

The molar mass of a naturally occurring mixture of isotopes is the weighted average of the isotopic molar masses. Each isotope contributes to the total in proportion to its percentage (fractional) abundance, and the average is calculated using Equation. ... 

First, the percentages must be converted to fractions by dividing by 100%. Then we multiply these fractional abundances by the Isotopic masses and add the results. A table helps in organizing these manipulations ... 

Look again at the percentage distribution of the isotopes of iron. Just over 90% of the... 

C02-0051. Platinum has four stable isotopes whose mass numbers and percentages are 194, 32.9% 195,... 

The isotopic signature of the nuclear fission of different percentages. 

The usual percentage of U is 0.7207%, but the Oklo deposits contain 0.7071% of this isotope. This... 

Enrichment, Isotopic—An isotopic separation process by which the relative abundances of the isotopes of a given element are altered, thus producing a form of the element that has been enriched in one or more isotopes and depleted in others. In uranium enrichment, the percentage of uranium-235 in natural uranium can be increased from 0.7% to >90% in a gaseous diffusion process based on the different thermal velocities of the constituents of natural uranium (234U, 235U, 238U) in the molecular form UF6. 

C coupling has very little significance in everyday proton NMR interpretation, though it has been used in the past to crack specific problems by means of selective enrichment of a specific carbon during synthesis, with a greater than normal percentage of 13C isotope, which makes detection easy. 

Fig. 4. Hydrogen isotope exchange between C6H and C6D6. Correlation of randomisation rate constant kF, with percentage d-character of the metallic bonds (4). 

Table I presents the average aerodynamic distributions of Pb-212 and Pb-214, as well as the frequency with which Pb-214 or Pb-212 was the dominant isotope in each size range. The Aitken nuclei fraction (below 0.08 pm) contained a higher percentage of Pb-212 activity compared with Pb-214 in 69.6% of the measurements. The predominance of Pb-212 in this fraction is also illustrated by the distributions reported in Figure 1. In the remaining measurements, where Pb-214 was fractionally more abundant below 0.08 um, the disparity between the relative amounts of each isotope was not nearly as dramatic. Conversely, Figure 1 and Table I illustrate that Pb-214 is generally enriched in the accumulation mode aerosol, particularly between 0.11 and 0.52 ]xm, where most of the surface area and mass occurs.

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. 

Highly enriched samples of isotopic purities ranging from 84% to 99% have been prepared for most of the isotopes of tin. Typical percentage compositions for enriched samples of tin(IV) oxide are given in Table 633. 

Fig. 1.5. Paths of the r-, s- and p-processes in the neighbourhood of the tin isotopes. Numbers in the boxes give mass numbers and percentage abundance of the isotope for stable species, and /9-decay lifetimes for unstable ones. 116Sn is an s-only isotope, shielded from the r-process by 116Cd. After Clayton et al. (1961). Copyright by Academic Press, Inc. Courtesy Don Clayton.

Because of the differing rates of the component reactions, the CNO cycle modifies the initial composition of the material, which typically has O > C > N, making more 14N (and more 13C relative to 12C) at the expense of carbon and (at the higher temperatures) oxygen. Thus in H-buming zones the CN mixture is rapidly modified, and the CNO mixture somewhat more slowly modified, to reach steady-state ratios,4 e.g. at T = 3 x 107 K the steady-state percentages of CNO isotopes, compared to Solar-System values, are as follows ... 

---