Iodine flux

A series of other halogenated compounds have been identihed in seawater, including ethyl iodide, propyl iodide, bromoiodomethane, chloro-iodomethane, and di-iodomethane (Carpenter et al., 2000 Klick and Abrahamsson, 1992). Little is known about their production mechanisms. Loss mechanisms are likely to include photolysis and reaction with chloride and hydroxide ions. Information is too limited to be used to derive global fluxes for these compounds, although the data available indicate that a reasonable case can be made that the iodine flux from these compounds is similar to that from CH3I. 

Ullman, W. J., and Aller, R. C. (1980). Dissolved iodine flux from estuarine sediments and implications for the enrichment of iodine at the sediment-water interface. Geochim. Cosmochim. Acta 44 (in press). 

Contrast Injection parameters that determine attenuation within the tissue of interest are duration of injection and iodine administration rate or iodine flux. The... 

Arterial enhancement depends on iodine administration rate (or iodine flux) and can be controlled by the injection flow rate (ml/s) and/or the iodine concentration of the contrast medium (mgl/ml) (Fleischmann et al. 2000) (Fig. 8.3). Most of the angiography protocols used on 64-detector-row scanners today utilize very... 

The strength of an individual s attenuation response to intravenously injected contrast dye is controlled by cardiac output and blood volume, both correlate with body weight. An individual contrast application protocol should therefore be adapted to patient body weight. Whereas the iodine flux rates of Table 8.2 apply for the average 75-80-kg patient, lower flux rates apply for slim patients and higher flux rates for heavier ones. Weight-adapted protocols are less important for vascular attenuation than for parenchymal contrast imaging, but should nevertheless be used in order not to overdose slim patients. 

The main factor in relation to arterial enhancement is iodine flux (mg of iodine entering the cir-... 

Account must be taken in design and operation of the requirements for the production and consumption of xenon-135 [14995-12-17, Xe, the daughter of iodine-135 [14834-68-5] Xenon-135 has an enormous thermal neutron cross section, around 2.7 x 10 cm (2.7 x 10 bams). Its reactivity effect is constant when a reactor is operating steadily, but if the reactor shuts down and the neutron flux is reduced, xenon-135 builds up and may prevent immediate restart of the reactor. 

The next set of experiments were designed to compare chlorine with bromine and iodine in terms of membrane sensitivity. Experiments with A-2 and X-2 were run for forty hours but U-1 was exposed for only 16 hours because of rapid deterioration on exposure to bromine. Concentrations of all halogens were equivalent to 3 ppm CI2 on a molar basis. Performance profiles for membranes U-1, A-2 and X-2 are shown in Figures 8, 9, and 10 respectively. Only product flux is reported in this case since it appears to be a more sensitive indicator of performance changes. 

If the drift-weed were to be burnt to a loose ash, it would furnish 25 to 30 lbs. of iodine per ton in practice, it rarely contains more than 12 lbs. per ton. The low yield is due to faulty treatment in calcination-—e.g. (i) burning at too high a temp, which causes the volatilization of part of the iodine, and the fusion or fluxing of the ash with sand and pebbles and (ii) imperfect protection of the kelp-ash from the weather whereby some of the soluble iodides are washed out by rain. High temp, burning also reduces some of the sulphates to sulphides, which later causes a high consumption of acid per unit of iodine. 

The diffusion coefficients for iodine are close to those measured previously in the same glass (12) at the experimental temperatures. However, the activation energies of these two measurements differ. The experiments differ to some degree in that iodine and other fission products were made from dissolved U02 in this experiment, while iodine only was made from Te02 under a neutron flux in the previous experiment. The latter mode of formation should lead to a greater excess of oxygen in the glass. 

C") Chlorite-iodine-reductant. These systems, which include systems 8 b, 9 b and 10b of Table 8 appear to be only minor variants of type C ) in which (M 9) replaces (M 8). C ") Chlorite-iodide-reductant. The only known example of this type is the chlorite-iodide-malonic acid system, which is of special interest because it supports both batch oscillations and spatial wave patterns. The slow decomposition of iodinated malonic acid species apparently provides a long lasting, indirect flux of iodide (via (M2) + (M9)) in this system. 

It can easily be seen that the total yield of partial chemical reactions (2.182) and (2.19]) is zero. This is caused by the presence of the third, low-mobile component (iodine anions I ). Because of their presence, rubidium and silver cations are unable to move in the lattices of the growing Rb 2AgI3 and RbAg4J5 compounds independently of each other. The fluxes of these cations should necessarily be balanced since partial chemical reactions (2.18]) and (2.192) are mutually dependent. In this respect, the system under consideration and other similar systems differ from binary ones in which all four partial chemical reactions taking place at layer interfaces are independent of each other unless any diffusional constraints arise (see the next chapter). 

Quaternary germicides, phenolic compounds and iodine are not recommended as sanitizing against for polyamide membranes as these compounds can cause losses in water flux through the membrane.15... 

The main conclusions from the early model studies on iodine chemistry remain valid there is a significant lack of information on the kinetics of reactive iodine (especially lO and OIO reactions paths to stable particulate iodine) and on fluxes of alkyl iodides from the oceans. Nevertheless, important progress has recently been made and work is currently ongoing in several laboratories worldwide. This is an important area of atmospheric research in need of more attention. 

Baker A. R., Tunnicliffe C., and Jickells T. D. (2001) Iodine speciation and deposition fluxes from the marine atmosphere. J. Geophys. Res. 106, 28743-28749. 

Iodine-129 has major sources in both surface and subsurface environments. It is produced in the atmosphere by cosmic-ray spallation of xenon and in the subsurface by the spontaneous fission of uranium. Iodine-129 of subsurface origin is released to the surface environment through volcanic emissions, groundwater discharge, and other fluxes. Due to its very long half-life, 15.7 Ma, these sources are well mixed in the oceans and surface environment, producing a specific activity of 5 xBq (g I) (equivalent to a I/I ratio of 10 ). Due to its low activity, the preferred detection method of I is AMS (Elmore et al., 1980). 

Campos M. L. A. M., Nightingale P. D., and Jickells T. D. (1996) A comparison of methyl iodide emissions from seawater and wet depositional fluxes of iodine over the southern North Sea. Tellus 48B, 106-114. 

Most of the research was done with 0.2 micrometer rated porous polypropylene (Accurel ) membrane, and the concentration of polyacetylene in the composite could be varied from 4 to 43 percent. Larger percentages should be possible. The membranes did not lose their flexibility, and membrane properties such as flux rates and bubble point pressure were not altered (see Experimental Procedure 1). As is the case for polyacetylene alone, the conductivity of these membranes could be varied depending upon the type and amount of dopant. Iodine doped laminates were the most stable of the two doped laminates investigated in this study. 

---