Iodide, iodine distribution

Alterations in background by contamination with other frequently used radioisotopes Since fluorescent thyroid scans are often performed to evaluate further the findings initially obtained from a pertechnetate or sodium iodide scan, the effect of these radioisotopes on quantitation and imaging of iodine distribution was evaluated by x-ray fluorescence. Figure 9 shows the 99mTc spectrum with the source shutter of the instrument closed. 

Strong iodide solutions act by decreasing the vascularity of the thyroid gland by rapidly inhibiting the release of the thyroid hormones. Radioactive iodine is distributed within the cellular fluid and excreted. The radioactive isotope accumulates in the cells of the tiiyroid gland, where destruction of tiiyroid cells occurs without damaging other cells throughout the body. 

This reaction undergoes conversion in one sequence of consecutive elementary reaction steps and so only one propagating front is formed in a spatially distributed system [68]. Depending on the initial ratio of reactants, iodine as colored and iodide as uncolored product, or both, are formed [145]. 

In a technique known as medical imaging, tracers are used in medicine for the diagnosis of internal disorders. Small amounts of a radioactive material, such as sodium iodide, Nal, which contains the radioactive isotope iodine-131, are administered to a patient and traced through the body with a radiation detector. The result, shown in Figure 4.11, is an image that shows how the material is distributed in the body. This technique works because the path the tracer material takes is influenced only by its physical and chemical properties, not by its radioactivity. The tracer may be introduced alone or along with some other chemical, known as a carrier compound, that helps target the isotope to a particular type of tissue in the body. 

The observation of rather similar bimodal distributions in polymers prepared using iodine as initiator (164) tends to confirm this idea, since contributions from covalent iodides are quite likely. 

By using radioactive iodine-131 as scavenger and identifying the alkyl iodides formed, by isotopic dilution analysis, much information can be obtained as to the nature of the radicals produced82-84. Some typical product distributions are shown in Table 9. 

Nakayama, E., Kimoto, T., Isshiki, K., Sohrin, Y. and Okazaki, S. (1989) Determination and distribution of iodide and total-iodine in the North Pacific Ocean by using a new automated electrochemical method. Mar. Chem., 27, 105-116. 

If the solution is titrated with standard sodium thiosulphate solution, the total concentration of the iodine, both as free I2 and combined as IJ, is obtained, since, as soon as some iodine is removed by interaction with the thiosulphate, a fresh amount of iodine is liberated from the tri-iodide in order to maintain the equilibrium. If, however, the solution is shaken with carbon tetrachloride, in which iodine alone is appreciably soluble, then the iodine in the organic layer is in equilibrium with the free iodine in the aqueous solution. By determining the concentration of the iodine in the carbon tetrachloride solution, the concentration of the free iodine in the aqueous solution can be calculated from the known distribution coefficient, and therefrom the total concentration of the free iodine present at equilibrium. Subtracting this from the total iodine, the concentration of the combined iodine (as Ij) is obtained by subtracting the latter value from the initial concentration of potassium iodine the concentration of the free KI is deduced. The equilibrium constant ... 

The angular distributions of recoiling iodine atoms were also measured for all four alkyl iodides studied. As is discussed elsewhere, such distributions provide information about the symmetry, configuration, and lifetime of the parent dissociative excited state. The details of these results will be presented in a future paper. Briefly, the angular distributions show that the transition dipole moment lies along the C—I bond and that the excited state breaks up on a time-scale short compared toarotational period. 

The lack of laser action in the photolysis of isopropyl iodide raises intriguing questions. As Husain and Donovan point out, this does not necessarily indicate the absence of population inversion, since under the laser experimental conditions there could instead be an insufficient absolute concentration of I atoms. Spectroscopic studies show that excited iodine atoms are produced from isopropyl iodide photodissociation, but at lower relative concentrations than for n-propyl iodide under similar conditions. Since the two propyl iodides show similar I quenching rates, it would appear most likely that a decreased I /I ratio is the reason stimulated emission is not seen. The present experiments, unfortunately, cannot provide a more quantitative explanation. The distinct broadness of the isopropyl iodide distribution in fig. 2 indicates a departure from the methyl- ethyln-propyl trend, and might represent comparable amounts of P and I atom production, with overlapping translational energy distributions, at least when viewed with our present... 

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