Important Isotopes

Probably the most important set of isotopes are those for carbon. There are three main isotopes of carbon, one with six neutrons (carbon-12, the 12 being the sum of the protons and neutrons), one with seven neutrons (carbon-13), and one with eight neutrons (carbon 14). Carbon-12 is the one which is used to define the atomic mass unit, as we have mentioned, and hence this isotope is of considerable importance. Approximately 99% of all carbon atoms are carbon-12. The carbon-14 isotope is also of considerable importance. It is used in determining the age of materials found in archeological discoveries. 

Finally, there are a number of isotopes that are radioactive, such as uranium isotopes. This means that their atoms spontaneously break apart into simpler atoms with time. This breaking apart is accompanied by dangerous radiation that is given off from the materials in which these elements are found, and special precautions must be taken by technicians who work with them. 

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Plutonium as the important isotope Pu is prepared in ton quantities in nuclear reactors. It is produced by the following reactions, wherein the excess neutrons produced by the fission of are captured by to yield Pu. 

Plutonium [7440-07-5] Pu, element number 94 in the Periodic Table, is a member of the actinide series and is metaUic (see Actinides and transactinides). Isotopes of mass number 232 through 246 have been identified. AH are radioactive. The most important isotope is plutonium-239 [15117-48-3] Pu also of importance are Pu, Pu, and Pu. 

The technologically most important isotope, Pu, has been produced in large quantities since 1944 from natural or partially enriched uranium in production reactors. This isotope is characterized by a high fission reaction cross section and is useful for fission weapons, as trigger for thermonuclear weapons, and as fuel for breeder reactors. A large future source of plutonium may be from fast-neutron breeder reactors. 

Fig. 18-24 Observed correlation (the Meteoric Water Line) of the two most important isotopic ratios in precipitation (gray diamonds Jouzel et al., 1987 and Dahe et al., 1994), and predictions of simple isotopic models. A, prediction with constant a B, prediction with temperature-dependent a.

One of the most important isotopes in nuclear medicine, Tc, is produced by bombarding molybdenum with... 

Americium (pronounced,, am-8- ris(h)-e-8m) is a man-made, radioactive, actinide element with an atomic number of 95. It was discovered in 1945. Actinides are the 15 elements, all of whose isotopes are radioactive starting with actinium (atomic number 89), and extending to lawrencium (atomic number 103). When not combined with other elements, americium is a silvery metal. Americium has no naturally occurring or stable isotopes. There are two important isotopes of... 

L5. Can you guess from data in the periodic table what the most important isotope of bromine is With the additional information that 8l,Br does not occur naturally, how can you amend that guess ... 

Ans. The atomic weight of Br is about 80, so one might be tempted to guess that w)Br is the most important isotope. Knowing that it is not, one then can guess that an about-equal mixture of 7<)Br and slBr occurs, which is correct. 

The end window of the tube must be thin enough to permit the weaker radiations to enter the tube (aluminium, 6-8 mg cm-2 mica, 2 mg cm-2) but even so alpha particles and very weak beta emissions are either completely or partially absorbed. The emissions from the biologically important isotopes of tritium and carbon-14 fall into this category and alternative detectors should be used for these isotopes. 

Equation 5.11 is important. It relates the experimentally observed vapor pressure ratio to the theoretically important isotope effects on the free energy differences and/or partition function ratios. This equation encapsulates the essential physics of the vapor pressure isotope effect and, as we shall see, provides a path for its theoretical interpretation in terms of molecular structure and dynamics via the partition function ratios. 

In deriving Equation 10.18 one assumes that the motions of the H, D, and T can be treated in the ZPE approximation and the only important isotope sensitive motions are the RH, RD, or RT stretching modes which shift significantly on the transfer from reactant to transition state. In the ZPE approximation... 

A deviation from the ideal fractionation law will appear as a residual correlation between the ratios corrected for mass bias using the exponential law. It can be verified that even very small 8M/M in Equation (40) produces a potentially important isotopic effect on the order of 1 + P(5M,. - 5Mt)/Mj. The alignment of the correlation between the corrected ratios x = hir and y = In rj produced by sloping peaks in a log-log plot has a slope of 5M,/8M,. For a rormd peak, the second-order term should be included. 

Californium is a synthetic radioactive transuranic element of the actinide series. The pure metal form is not found in nature and has not been artificially produced in particle accelerators. However, a few compounds consisting of cahfornium and nonmetals have been formed by nuclear reactions. The most important isotope of cahfornium is Cf-252, which fissions spontaneously while emitting free neutrons. This makes it of some use as a portable neutron source since there are few elements that produce neutrons all by themselves. Most transuranic elements must be placed in a nuclear reactor, must go through a series of decay processes, or must be mixed with other elements in order to give off neutrons. Cf-252 has a half-life of 2.65 years, and just one microgram (0.000001 grams) of the element produces over 170 mhhon neutrons per minute. 

Figure 1 Part from the Nuclide Chart with basic properties of important isotopes of rhenium and its...

NMR spectroscopy allows the organic chemist to see the environment surrounding the nuclei in a molecule. NMR isn t applicable to all nuclei however, most elements have one or more isotopes for which NMR is applicable. NMR spectroscopy may be used on nuclei that behave as small magnets. Organic chemists usually rely on H (proton) and as the most important isotopes because most organic compounds contain hydrogen and all organic compounds contain carbon. 

X 10 yr) and ends with stable ° Pb, after emission of eight alpha (a) and six beta (jS) particles. The thorium decay series begins with Th (ti/2 = 1.41 X 10 °yr) and ends with stable ° Pb, after emission of six alpha and four beta particles. Two isotopes of radium and Th are important tracer isotopes in the thorium decay chain. The actinium decay series begins with (ti/2 = 7.04 X 10 yr) and ends with stable Pb after emission of seven alpha and four beta particles. The actinium decay series includes important isotopes of actinium and protactinium. These primordial radionuclides, as products of continental weathering, enter the ocean primarily by the discharge of rivers. However, as we shall see, there are notable exceptions to this generality. 

SRM 979), Ni (nickel metal isotopic standard NIST SRM 986), Rb (rubidium chloride isotopic standard NIST SRM 984) and Sr (strontium carbonate isotopic standard NIST SRM 987). In addition, isotope reference materials are available for heavy elements such as T1 (thallium metal isotopic standard NIST SRM 997), Pb (NIST lead standard reference materials SRM 981-983) or U (uranium oxide NIST isotope standard U 005, U020, U350, U500 or U930) and others. The most important isotope standard reference materials applied in inorganic mass spectrometry are summarized in the table in Appendix V.17... 

Early in 1941, 239Pu, the most important isotope of plutonium was discovered by Kennedy, Segre, Wahl, and Seaborg. 239Pu was produced by the decay of 239Np, which in turn was produced by the irradiation of 238U by neutrons, using the reaction discovered by McMillan... 

This example illustrates how m/e values of ions that differ only in isotopic composition can be used to determine elemental compositions. The important isotopes for this purpose in addition to those of chlorine are the stable isotopes of natural abundance, 13C (1.1%), 15N (0.37%), 170 (0.04%), lsO (0.20%). As a further example, suppose that we have isolated a hydrocarbon and have determined from its mass spectrum that M + = 86 mass units. In the absence of any combination reactions there will be an (M + 1)+ ion corresponding to the same molecular ion but with one 13C in place of 12C. The intensity ratio (M + 1 )+/M+ will depend on the number of carbon atoms present, because the more carbons there are the greater the probability will be that one of them is 13C. The greater the probability, the larger the (M + 1 )+/M+ ratio. For n carbons, we expect... 

In recognition of these needs, a list of recommended half-life values for a number of actinide nuclides useful as standards for nuclear-data measurements was prepared several years ago [VAN83]. This list included both total and partial half-life data for 11 such nuclides - the important isotopes of U, Np and Pu, as well as 252Cf. Subsequently, these data were revised [REI85a] to incorporate the results of new measurements, some of them from the work of the CRP. These data are given in a recent paper [REI85b], as well as in the final report of the IAEA CRP. 

As mentioned above, 57Fe is the most important isotope that exhibits the Mossbauer effect and Mossbauer spectra provide valuable information about the chemical environments of iron nuclei. At the trivial level it is able to provide quantitative discrimination between Fe11 and Fem non-invasively, a valuable technique particularly for unstable samples such as, for example, air-sensitive sediments. Also, because the technique is specific for individual isotopes, it is able to detect and identify small amounts of iron-rich phases in the presence of large quantities of other compounds. A good example here is the case of soil and mineral specimens, where the various oxide and oxyhydroxide species can all be distinguished from one another on the basis of their Mossbauer spectra at different temperatures (see e.g. Goodman, 1994). 

Natural Abundance of Important Isotopes Rules for Determination of Molecular Formula Neutral Moieties Ejected from Substituted Benzene Ring Compounds Order of Fragmentation Initiated by the Presence of a Substituent on a Benzene Ring... 

Neutron activation of the stable isotopes of iron produces two radioactive isotopes—55Fe and 59Fe. 55Fe (half-life = 2.685 years), which is a beta (electron-capture) emitter and decays to the stable 55Mn isotope, is the more important isotope.10... 

Besides the research use of 249Bk for the characterization of the chemical and physical properties of element 97, its relatively rapid decay to 249Cf (0.2% per day) makes it a valuable source of this important isotope of californium for chemical study. This genetic relationship has been exploited in studies of the chemical consequences of beta (fi) decay in the bulk-phase solid state (12, 13). 

Table 3-1 Decay Properties of Some Biochemically Important Isotopes...

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