Carbon nuclides

A radioactive /3-emitting (0.156 MeV) carbon nuclide. The decay half-life is 5715 years. 

Self-Test 17.2B Identify the nuclide produced and write the nuclear equation for (a) electron capture by iron-55 (b) positron emission by carbon-1 1. 

The constant half-life of a nuclide is used to determine the ages of archaeological artifacts. In isotopic dating, we measure the activity of the radioactive isotopes that they contain. Isotopes used for dating objects include uranium-238, potassium-40, and tritium. However, the most important example is radiocarbon dating, which uses the decay of carbon-14, for which the half-life is 5730 a. 

Because the masses of nuclides are so small, they are normally reported as a multiple of the atomic mass constant, ma (formerly atomic mass unit, amu). The atomic mass constant is defined as exactly V12 the mass of one atom of carbon-12 ... 

An interesting study of the recoil behaviour of different nuclides in metal carbonyls was made by Harbottle and Zahn . They studied Cr(CO)6 and Mo(CO)g irradiated in various ways so as to produce nuclear reactions in oxygen and carbon, as well as both high and low energy reactions in Cr and Mo. The results can be briefly summarized as in Table 9. 

Write the nuclear symbols for the following nuclides (a) the one that contains 92 protons and 143 neutrons and (b) the carbon isotope that has 8 neutrons. 

C22-0054. Identify the compound nucleus and final product resulting from each of the following nuclear reactions (a) carbon-12 captures a neutron and then emits a proton (b) the nuclide with eight protons and eight neutrons captures an a particle and emits a y ray and (c) curium-247 is bombarded with boron-11, and the product loses three neutrons. 

C22-0104. State why each of the following nuclides is unstable (a) carbon-14 (b) plutonium-244 (c) Mil and (d) a lithium nucleus with five neutrons. 

Chapters 11 and 12 focus on the oceans. The first of these describes the use of U-series nuclides in the modern ocean, where they have been particularly useful during the last decade to study the downward flux of carbon. The second ocean chapter looks at the paleoceanographic uses of U-series nuclides, which include assessment of sedimentation rates, ocean circulation rates, and paleoproductivity. Both of these ocean chapters demonstrate that knowledge of the behavior of the U-series is now sufficiently well developed that their measurement provides useful quantitative information about much more than just the geochemistry of these elements. 

This chapter summarizes the use of U-series nuclides in paleoceanography. It starts with a brief summary of the oceanic U budget and an introduction to important features of the behavior of U-series nuclides in the marine realm. It then discusses the various U-series tools which have proved useful for paleoceanography, starting at U (and U) and progressing down the decay chain towards Pb. One tool that will not be discussed is U/Th dating of marine carbonates which has seen sufficient application to merit a chapter on its own (Edwards et al. 2003). The use of U-series nuclides to assess rates of processes in the modem ocean will also not be discussed in depth here but are dealt with elsewhere in this volume (Cochran and Masque 2003). 

Radium, like most other group II metals, is soluble in seawater. Formation of Ra and Ra by decay of Th in marine sediments leads to release of these nuclides from the sediment into the deep ocean. Lead, in contrast, is insoluble. It is found as a carbonate or dichloride species in seawater (Byrne 1981) and adheres to settling particles to be removed to the seafloor. 

Atomic Mass (u)—The mass of a neutral atom of a nuclide, usually expressed in terms of "atomic mass units." The "atomic mass unit" is one-twelfth the mass of one neutral atom of carbon-12 equivalent to 1.6604xl0 24 g. 

Table 2.2 lists the most important syntheses occurring in the stars. The main products include the bioelements C, O, N and S. The synthesis of the elements began in the initial phase after the big bang, with that of the proton and the helium nucleus. These continue to be formed in the further development of the stars. The stable nuclide 4He was the starting material for subsequent nuclear syntheses. Carbon-12 can be formed in a triple a-process, i.e., one in which three helium... 

Base SI units Amount of substance mole mol Amount of substance which contains as many specified entities as there are atoms of carbon-12 in exactly 0.012 kg of that nuclide. The elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles. 

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