Emanation techniques

By a decay of the daughter nuclide receives a recoil. Depending on the penetration depth of Pb, a greater or smaller fraction of the recoiling atoms are sampled on a copper electrode (potential —200 V), and the activity of T1 is measured. Application of the recoil method is restricted to a emitters yielding a radioactive daughter nuclide. 

The sensitivity of the measurement of diffusion coefficients in solids depends primarily on the method applied. By the radiation-absorption method mentioned above, diffusion coefficients down to about 10 ° cm s can be measured in the case of p emitters and down to about 10 cm s in the case of a emitters. The recoil method makes it possible to measure diffusion coefficients down to the order of 10 cm s . Relatively low sensitivity D 10 cm s ) is achieved with the method of mechanical slicing, whereas diffusion coefficients down to about 10 cm s are obtained with the method of dissolution in steps. Mechanical slicing and dissolution in steps have the advantage that the actual concentration in the solid is obtained. 

Examples of Ihe deterniinalioii of self-diffusion coefficients in solids are Ihe diffusion of hydrogen ions and water molecules (labelled with T and O, respectively) in alums, of Cl (labelled with Cl) in AgCl, and of 1 (labelled with l) in Agl. Besides self-diffusion, many other diffusion coefficients of trace elements in metals, oxides, silicates and other substances have been determined by application of radio-tracers. Investigation of the migration of trace elements from solutions into glass revealed fast diffusion of relatively small monovalent ions such as Ag+. 

In measuring diffusion in liquids or gases, mixing by convection must be excluded. Several experimental arrangements are described, for example use of a diffusion tube, a diaphragm or a capillary. Measurement of the diffusion coefficient of pH-sensitive species as a function of pH allows conclusions with respect to the size of the species. 

Emanation techniques are based on the production of radioactive noble gases by decay of mother nuclides or by nuclear reactions. The emanating power has been defined by Hahn as the fraction of radioactive noble gas escaping from a solid relative to the amount produced in the solid. It depends on the composition of Ihe solid, ils lallice structure and its spccihc smTace area. Reactions in the solid have a major inlluence. Further factors affecting the emanating power are the half-life of the noble gas radionuclide, its recoil energy and the temperature. 

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Emanation techniques are also used for the study of reactions between two solids, for instance the formation of PbSiOs (as in the preparation of lead glass) by the reaction... 

The ageing of thorium hydroxide and iron hydroxide in the presence of water is obvious from Fig. 18.8. Whereas the emanating power of thorium hydroxide decreases very slowly, that of iron hydroxide falls olf relatively fast, indicating faster ageing. Emanation techniques have also been applied to obtain information about surface areas and densities of porous substances. 

An explosion model is used to predict the overpressure resulting from the explosion of a given mass of material. The overpressure is the pressure wave emanating from a explosion. The pressure wave creates most of the damage. The overpressure is calculated using a TNT equivalency technique. The result is dependent on the mass of material and the distance away from the explosion. Suitable correlations are available (2). A detailed discussion of source and consequence models may be found in References 2, 8, and 9. 

The accuracy of the results emanating from the program depends on how well the individual simulation equations predict the real outputs. When better estimating techniques become available, the old equations should be replaced by more accurate or faster ones. This means the equations should be continuously updated, like the cost data in a previous example. 

Fleischer, R. L. and A. Mogro-Campero, Mapping of Integrated Radon Emanation for Detection of Long-Distance Migration of Gases Within the Earth Techniques and Principles,. 1. Geophvs. Res. 83(B7) 3539-3549 (1977). 

Despite their vast untapped potential, techniques like fluorous biphasic catalysis still have limitations. These limitations center on solubility and emanate directly from the strengths of the technique heavily fluorous compounds tend to be highly insoluble in organic solvents while organic compounds (especially polar ones) tend to be highly... 

In situ EPR spectroelectrochemistry monitors paramagnetic species, usually radicals in solution. The chemical stability of such species can be readily determined by this technique. It was seen that the most conunon problems encountered with in situ electrochemical EPR work emanate from the use of absorbing solvents and polymers containing paramagnetic impurities. 

It is instructive to compare the data emanating from different force measurement techniques. This requires a conversion of the disjoining pressure in energy per unit area. By integration over the thickness of the disjoining pressure, one obtains the corresponding energy per unit area, E h), between two infinite planes ... 

Until recently, previous studies for continuous monitoring of hepatic function with ICG utilized the absorption mode. However, new studies demonstrate that the highly sensitive fluorescence technique can equally be used [148-150]. In addition to high sensitivity, in-depth analysis of the emission, excitation and polarization properties of fluorescence spectroscopy furnishes additional functional information about the dye molecule. In this system, the fluorescence profile emanating from the clearance of injected biocompatible dye is monitored with a small photodetector. Fig. 8 shows the in vivo fluorescence detection apparatus developed for continuous monitoring of organ functions [147,148]. 

In another study, Darrach et al. [2] reported that samples collected near intact UUXO targets contained traces of explosives at up to parts per billion (ppb) concentration levels. The samples were analyzed in the laboratory, using solid-phase microextraction (SPME) to extract target analytes from the samples. The samples were then processed using a reversal electron attachment detection (READ) technique. If the levels of contamination found in these studies are representative of that emanating from most UUXO, the implication is that sensitive chemical sensors such as the SeaDog may be useful for detecting UUXO. 

Atmospheric Pressure Chemical Ionization (APCI) is coupled to Tandem Mass Spectrometry (MS/MS) for the purpose of analyzing vapor phase perfume mixtures. Air-borne fragrances are analyzed directly by APCI/ MS/MS without the need for time consuming and potentially adulterating trapping and chromatography steps. Volatile fragrance chemicals have been rapidly identified by this novel technique as they emanate from vials or directly from skin. 

To rate the polarity of solid surfaces from their heats of immersion in simple organic liquids having different peripheral dipole moments. For the first time, this technique allows an experimentally derived number to be put on the average force field emanating from solid surfaces. 

The value of the ratio Ne/N0 does not imply that all excited atoms return to their initial state as they emit a photon. As the temperature increases, the emission spectrum becomes more complex, particularly due to the emission of lines emanating from ionised atoms (see Fig. 14.3). It thus becomes necessary to have good quality optics in order to use this technique. The corresponding instruments are atomic emission spectrophotometers, which will be discussed in Chapter 15. 

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