Decay after-effects studied using

The nuclear decay of radioactive atoms embedded in a host is known to lead to various chemical and physical after effects such as redox processes, bond rupture, and the formation of metastable states [46], A very successful way of investigating such after effects in solid material exploits the Mossbauer effect and has been termed Mossbauer Emission Spectroscopy (MES) or Mossbauer source experiments [47, 48]. For instance, the electron capture (EC) decay of Co to Fe, denoted Co(EC) Fe, in cobalt- or iron-containing compormds has been widely explored. In such MES experiments, the compormd tmder study is usually labeled with Co and then used as the Mossbauer source versus a single-line absorber material such as K4[Fe(CN)6]. The recorded spectrum yields information on the chemical state of the nucleogenic Fe at ca. 10 s, which is approximately the lifetime of the 14.4 keV metastable nuclear state of Fe after nuclear decay. 

Luminescence decay curves are also often used to verify that samples do not contain impurities. The absence of impurities can be established if the luminescence decay curve is exponential and if the spectrum does not change with time after pulsed excitation. However, in some cases, the luminescence decay curve can be nonexponential even if all of the luminescing solutes are chemically identical. This occurs for molecules with luminescence lifetimes that depend upon the local environment. In an amorphous matrix, there is a variation in solute luminescence lifetimes. Therefore, the luminescence decay curve can be used as a measure of the interaction of the solute with the solvent and as a probe of the micro-environment. Nag-Chaudhuri and Augenstein (10) used this technique in their studies of the phosphorescence of amino acids and proteins, and we have used it to study the effects of polymer matrices on the phosphorescence of aromatic hydrocarbons (ll). 

It may seem that even after 6 hours of reaction, WPG is insufficiently low to impart decay resistance to wood. The rate of vapor phase reactions is determined by the rate of permeation of reagent vapors into the wood. It has been observed that even longitudinal permeability of wood decreased by 2-10 times during acetylation (38). This probably is the reason for slow increase in WPG. In chir also a WPG of 7 percent and 10.9 percent was observed in four and eight hours acetylation respectively. In an earlier study using only 0.25 cm thick samples a WPG of 16.67% was obtained in four hours (35). Similar limitations were observed by Tarkow et al (37), who concluded that 3 mm thickness was the most optimum to obtain uniform acetylation. The effect of cross-section on acetylation is quite clear in Table II. 

In general, these results are in agreement with distribution studies, using V-labelled BMOV (7a in Figure 5.2) and vanadyl sulfate.P l The isotope is a jS+ and y emitter, and decays with = 16 days to Ti. In particular, these studies showed that BMOV is more effectively distributed towards the tissues (and less effectively secreted) than vanadyl sulfate over a period of 24 h, both when applied orally and intraperitoneally to rats. The highest concentrations were found in bone, followed by kidney and liver. The residence time in bone is 11 days for vanadium delivered in the form of vanadyl sulfate, and 31 days for BMOV. The amount of V excreted in the faeces 24 h after oral gavage were estimated to be 75% for vanadyl sulfate and 62% for BMOV. On the basis of other studies, absorption of orally administered vanadium is much lower and comes close to 1 % in the case of vanadyl sulfate. 

N diffuses into the structural pores of clinoptilolite 10 to 10 times faster than does CH4. Thus internal surfaces are kinetically selective for adsorption. Some clino samples are more effective at N2/CH4 separation than others and this property was correlated with the zeolite surface cation population. An incompletely exchanged clino containing doubly charged cations appears to be the most selective for N2. Using a computer-controlled pressure swing adsorption apparatus, several process variables were studied in multiple cycle experiments. These included feed composition and rates, and adsorber temperature, pressure and regeneration conditions. N2 diffusive flux reverses after about 60 seconds, but CH4 adsorption continues. This causes a decay in the observed N2/CH4 separation. Therefore, optimum process conditions include rapid adsorber pressurization and short adsorption/desorp-tion/regeneration cycles. 

The different emission products which are possible after photoionization with free atoms lead to different experimental methods being used for example, electron spectrometry, fluorescence spectrometry, ion spectrometry and combinations of these methods are used in coincidence measurements. Here only electron spectrometry will be considered. (See Section 6.2 for some reference data relevant to electron spectrometry.) Its importance stems from the rich structure of electron spectra observed for photoprocesses in the outermost shells of atoms which is due to strong electron correlation effects, including the dominance of non-radiative decay paths. (For deep inner-shell ionizations, radiative decay dominates (see Section 2.3).) In addition, the kinetic energy of the emitted electrons allows the selection of a specific photoprocess or subsequent Auger or autoionizing transition for study. 

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