Radioactive isotopes carbon-14 production

Carbon dating A process that uses the relative abundance of the radioactive isotope carbon-14 to determine the age of the remains or products of living things can be used for materials up to about 60,000 years old. 

The quantification of gross root production, rhizodeposition, microbial assimilation, and the production of organic materials in soil has made increasing progress ever since stable ( C) and radioactive ( C) carbon isotopes have been used (see Chap. 12). Measurements of soil organic matter dynamics without these isotopes are difficult due to the large amount present as compared to the smaller rates of input. 

The new product, which they named radionitrogen, was a hitherto unknown radioactive isotope of ordinary nitrogen. It disintegrates with a half period of fourteen minutes and expulsion of positrons, forming a stable, inactive isotope of carbon ... 

Schayer236 has recently studied the metabolism of epinephrine containing isotopic carbon. di-i8-Epinephrine-C14 fed to rats gave rise to the excretion of a conjugated, ether-soluble product containing radioactivity, but, after subcutaneous injection of methyl-di-epinephrine-C14, no activity was found in the ether-soluble fraction of urine. 

After a new (and unusual) mechanism, such as the benzyne mechanism for nucleophilic aromatic substitution, is proposed, experiments are usually designed to test that mechanism. A classic experiment supporting the benzyne mechanism used a radioactive carbon label. Examination of the mechanism shown in Figure 17.6 shows that the carbon bonded to the leaving chlorine and the carbon ortho to it become equivalent in the benzyne intermediate. Consider what would happen if the carbon bonded to the chlorine were a radioactive isotope of carbon (l4C) rather than the normal isotope of carbon (I2C). If we follow the position of the radioactive carbon label through the mechanism of Figure 17.6, we find that the label should be equally distributed between the carbon attached to the amino group in the product and the carbon ortho to it. 

Brown SA, Neish AC (1959) Studies of lignin biosynthesis using isotopic carbon VIII Isolation of radioactive hydrogenolysis products of lignin J Am Chem Soc 81 2419-2424... 

In Section 13.5 we learned that the isotope was used to determine the source of O2. The radioactive isotope helped to determine the path of carbon in photosynthesis. Starting with " C02, it was possible to isolate the intermediate products during photosynthesis and measure the amount of radioactivity of each carbon-containing compound. In this manner the path from CO2 through various intermediate compounds to carbohydrate could be clearly charted. Isotopes, especially radioactive isotopes that are used to trace the path of the atoms of an element in a chemical or biological process, are called tracers. 

There are four stable isotopes of strontium that are found naturally. In addition there are about twenty radioactive isotopes, including strontium-90, a deadly by-product of nuclear-bomb detonations. The natural forms of strontium are relatively nontoxic. Similar to calcium both physically and chemically, elemental strontium is a soft, shiny metal. Like calcium and other alkaline earth metals, it is easily oxidized and thus not found naturally in its free elemental state. Instead, it almost always is found in the + 2 oxidation state, forming such compounds as strontium oxide (SrO), strontium sulfate (SrS04, from the mineral celestite), strontium carbonate (SrCOj, from the mineral strontianite), and strontium chloride (SrC. Strontium nitrate, Sr(N03)2, is used to produce the brilliant red color seen in some fireworks and signal flares and is also used in making tracer bullets that can be seen when fired at night. Other strontium compounds are sometimes used in the manufacture of special glasses. Yet overall, strontium is not a very important element industrially or commercially, see ALSO Davy, Humphry... 

Although many radioactive isotopes have been discovered or prepared, most known nuclei are stable. Although it is not possible to explain nuclear stability theoretically, empirical observations allow one to guess the likely stability of any particular nuclide. A useful guide is a graph of the number of protons, Z, versus the number of neutrons in the stable nuclei, or the nucleon number (Figure 16.5). A narrow strip, the band of stability, is found, within which the nuclei are stable. Nuclei above the band of stability tend to emit positrons or to incorporate an outer electron into the nucleus (called electron capture) so as to move the product nucleus nearer to the band of stability. Nuclei below the band of stability tend to emit electrons for the same reason. Thus carbon-14 has a proton-to-neutron ratio of 6/8 (i.e. 0.75). This is well below the band of stability, and carbon-14 would be expected to decay by (3-emission, which is in accord with experimental evidence. All nuclei with more than 82 protons are radioactive. Only a small number of stable nuclei have odd numbers of protons or neutrons. Most stable nuclei contain an even number of protons or neutrons. There are only four stable nuclei that contain an odd number of both protons and neutrons jH, Li, N. Nuclei that contain 2, 8, 20, 28, 50, 82 and 126 protons or neutrons... 

The above example is very simple where the method of conventional organic synthesis did not need to be modified much. There are. however, other labeled s)mtheses where the organic synthesis method has to be modified profoimdly. One such example is the mthesis of DL-lysine labeled in the e-carbon atom. One interesting problem arises here. Since this synthesis is a multistep process, the isotope can be introduced either at an early step in the experiment, or in a later step. The latter option seems ro firom the point of view of conserving the radioactive isotope. However, it is experimentally found that introduction of isotope at a later step in the experiment does not yield the desired product. Therefore, even though the yield would be less, it is necessary that liie isotope be introduced at an early step in the mthesis. The reaction steps are givert low. 

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