Isotope / isotopic

Types of Dia.gnostic Isotopes. Isotopes used in nuclear medicine may be characterized by the source used to produce the radioactive isotope, by whether the isotopes are produced at a central location and shipped or at the clinic, or by the type of emission and thus the equipment used to detect them. The first of these, the sources, are summarized in Table 2. Some isotopes may be produced by more than one method. 

A special type of substituent effect which has proved veiy valuable in the study of reaction mechanisms is the replacement of an atom by one of its isotopes. Isotopic substitution most often involves replacing protium by deuterium (or tritium) but is applicable to nuclei other than hydrogen. The quantitative differences are largest, however, for hydrogen, because its isotopes have the largest relative mass differences. Isotopic substitution usually has no effect on the qualitative chemical reactivity of the substrate, but often has an easily measured effect on the rate at which reaction occurs. Let us consider how this modification of the rate arises. Initially, the discussion will concern primary kinetic isotope effects, those in which a bond to the isotopically substituted atom is broken in the rate-determining step. We will use C—H bonds as the specific topic of discussion, but the same concepts apply for other elements. 

Olafsson M, Eggler DH (1983) Phase relations of amphibole, amphibole-carbonate, and phlogopite-carbonate peridohte petrologic constraints on the asthenosphere. Earth Planet Sci Lett 64 305-315 Olson P, Schubert G, Anderson C, Goldman P (1988) Plume formahon and lithosphere erosion a comparison of laboratory and numerical experiments. J Geophys Res 93 15065-15084 Pearson DG, Shirey SB, Carlson RW, Boyd FR, Nixon PH (1995) Stabilisahon of Archean lithospheric manhe A Re-Os isotope isotope study of peridohte xenoliths. Earth Planet Sci Lett 134 341-357... 

The sum of the number of protons plus number of neutrons in the isotope is called the mass number of the isotope. Isotopes are usually distinguished from each other by their mass numbers, given as a superscript before the chemical symbol for the element. Carbon-twelve is an isotope of carbon with a symbol l2C. 

Element Isotope Isotope Type Abundance to All the Isotopes (%) Abundance to the Main Isotope (%) Element Type... 

All elements, by definition, have a unique proton number, but some also have a unique number of neutrons (at least, in naturally occurring forms) and therefore a unique atomic weight - examples are gold (Au Z = 79, N = 118, giving A =197), bismuth (Bi Z = 83, N = 126, A = 209), and at the lighter end of the scale, fluorine (F Z = 9, N = 10, A = 19) and sodium (Na Z = 11, N= 12, A = 23). Such behavior is, however, rare in the periodic table, where the vast majority of natural stable elements can exist with two or more different neutron numbers in their nucleus. These are termed isotopes. Isotopes of the same element have the same number of protons in their nucleus (and hence orbital electrons, and hence chemical properties), but... 

For elements that have three or more isotopes, isotopic fractionations may be defined using two or more isotopic ratios. Assuming that isotopic fractionation occurs through a mass-dependent process, the extent of fractionation will be a function of the relative mass differences of the two isotope ratios. For example, assuming a simple harmonic oscillator for molecular motion, the isotopic fractionation of may be related to as ... 

Note that if only one step, say the step, has a kinetic isotope isotope effect and there are no equilibrium isotope effects, then ... 

Symbol Fr atomic number 87 atomic weight 223 heaviest adtah metal element of Group lA (Group 1) a radioactive element electron configuration [Rn]7sk oxidation state -i-l the most electropositive element the most stable isotope, Fr-223 (ti/2 21 minutes), also is the only natural isotope. Isotopes, half-lives and their decay modes are shown below ... 

Each element exists as several isotopes. Isotopes of an element have identical atomic numbers, but different mass numbers (see Chapter 4). Therefore, isotopes of... 

As it turns out, most elements come in several different Vcirieties, called isotopes. Isotopes are atoms of the same element that have different mass numbers the differences in mass number cirise from different numbers of neutrons. The messy looking numbers with all those decimal places cire atomic masses. An atomic mass is a weighted averc e of the masses of all the naturally occurring isotopes of an element. Chemists have measured the percentc e of each element that exists in different isotopic forms. In the weighted averc e of the atomic mass, the mass of each isotope contributes in proportion to how often that isotope occurs in nature. More-common isotopes contribute more to the atomic mass. 

There can be varying numbers of neutrons in the atoms of an element. Most carbon atoms have six neutrons, but there are also carbon atoms with seven and eight neutrons. The differing numbers of neutrons does not affect the chemical properties of the atom. The different forms of an element that vary only in the number of neutrons in the atoms are called isotopes. Isotopes are named according to the total number of protons and neutrons they contain. Thus the isotopes of carbon with six, seven, and eight neutrons are called carbon-12, carbon-13, and carbon-14, respectively. Hydrogen has isotopes with one, two, and three neutrons. The most common form of hydrogen has only one neutron. 

So far, the analysis has been restricted to adsorption and exchange of isotopes (isotopic exchange). However, in most cases, the ion-exchange process involves the exchange of... 

Each element consists of between one and ten stable isotopes. Isotopes of an element have the same number of protons, which defines the element, but differ in the number of neutrons in the nucleus. For example, oxygen has eight protons and either eight, nine, or ten neutrons. The isotopes of oxygen are 160,170, and 180, with the numbers referring to the total number of protons + neutrons in the nucleus. The atomic number, Z, which is unique to each element, is the number of protons in the nucleus (equal to the number of electrons in the neutral atom). The atomic mass, A, is the number of protons plus the number of neutrons, N, in the nucleus (A = Z + N). Isotopes can either be stable or unstable (radioactive), and the... 

ELEMENT TARGET ISOTOPE ISOTOPIC ABUNDANCE (%) PRODUCT NUCLIDE HALF- LIFE THERMAL NEUTRON CROSS SECTION BEST y FOR MEASUREMENT (KEV) NUMBER OFy s PER 1000 DECAYS ASSOCIATED y -RAYS KEV MEASUREMENT POSSIBLE INTERFERING NUCLEAR REACTIONS PRODUCING NUCLIDES OF INTEREST... 

The mass spectrometer was developed by J.J. Thompson. In obtaining the mass spectrum of neon, he found a large signal at 20 amu, but also a small signal at 22 amu. He first assumed it was an impurity. So, he kept repeating the experiment, each time more and more carefully purifying the sample, but the small signal at 22 amu remained constant. What Thompson discovered was the existence of isotopes. Isotopes have the same atomic number but different mass number (same Z, different A), or the same number of protons and different number of neutrons. 

Isotope Isotopic Ratios" Isotopic Ratios (alternate) Percent atomic Abundance Total abundance (cm3 STP/g)6... 

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