Aluminium isotope

Chromium is used as an isotopic marker for aluminium. Taking into account that both chromium and aluminium cations diffuse in the same way, the results obtained on chromium diffusion coefficients in alumina scales can be applied to aluminium cation diffusion coefficients in the same scale. Indeed, it is easier to use a chromium isotope as a diffusive species than to use aluminium, which has no natural isotope one can only use an artificial aluminium isotope, Al, which is radioactive and very expensive. Very few works have used this radioactive tracer [90,101]. 

Emery, A. R., and R. C. Taylor Raman Spectra and vibrational Assignments of Aluminium borohydride and some isotopic Derivatives. Spectrochim. Acta 16, 1455 (1960). 

The largest class of meteorite finds is stony meteorites, made principally of stone. The general stony classification is divided into three subclasses called chondrites, carbonaceous chondrites and achondrites, and it is at this level of distinction at which we will stop. Before looking at their mineral and isotopic structure in more detail, it is useful to hold the composition of the Earth s crust in mind here for comparison. The Earth s crust is 49 per cent oxygen, 26 per cent silicon, 7.5 per cent aluminium, 4.7 per cent iron, 3.4 per cent calcium, 2.6 per cent sodium, 2.4 per cent potassium and 1.9 per cent magnesium, which must have formed from the common origin of the solar system. 

The most commonly used method for synthesizing organotin hydrides with a hydrogen isotope bonded to the tin atom is to reduce the appropriate chlorostannanes with labelled hydride reagents, such as lithium aluminium deuteride or sodium borodeuteride. For example, tributylchlorostannane can be reduced with lithium aluminium deuteride42-45 or deuterated or tritiated sodium borohydride46 to give tributyltin deuteride and tritiated tributyltin hydride, respectively (equations 40 and 41). 

The end window of the tube must be thin enough to permit the weaker radiations to enter the tube (aluminium, 6-8 mg cm-2 mica, 2 mg cm-2) but even so alpha particles and very weak beta emissions are either completely or partially absorbed. The emissions from the biologically important isotopes of tritium and carbon-14 fall into this category and alternative detectors should be used for these isotopes. 

The best illustration of radioactive astronomy is titanium-44. We shall take it as the archetype of a good radioactive isotope. It is relatively abundant and has a reasonable lifetime of around 100 years, neither too long, nor too short. Only aluminium-26 can rival it in this respect and nuclear gamma astronomy has already reaped some of the rewards (see Fig. 4.4). 

Fig. 4.4. All-sky map in the light of the 1.809 MeV gamma-ray hne from radioactive aluminium-26. The galactic distribution of aluminium-26, based on data from the COMPTEL (Compton Telescope) experiment aboard the GRO (Gamma-Ray Observatory), suggests that this isotope is dispersed across the Galaxy by the most massive stars, Wolf-Rayet stars and supernovas. Al is formed by the reaction Mg -b p — A1 -b y. This radioactive isotope has a lifetime of about million years and is ejected into space before it begins to decay.

We synthesized nine silicalites which had different concentrations of defect sites in the zeolite framework determined by isotope exchange method. These silicalites were treated with aluminium trichloride vapor under the same reaction conditions 923 K temperature, 1 h time, 11 kPa aluminium trichloride vapor pressure. Figure 1 shows the plots of the amount of aluminium atoms introduced into the framework against the amount of oxygen atoms on the defect sites. A... 

Direct evidence for a combination of catalytic fluorination and chlorination [4] was obtained from radiotracer studies in which fluorinated chromia catalysts were labelled with the short-lived (t /2 = 110 min) / + emitting isotope fluorine-18 [11]. Using this isotope it was possible to probe the interactions between HF and various fluorinated chromia catalysts more directly than had been possible hitherto. Three types of surface F-containing species were differentiated, weakly adsorbed HF which was easily removed by an inert gas flow, non-labile F, believed to be bound directly to surface Crin, and catalytically active F which could be incorporated into the organic products [12]. The controversy between dismutation (concerted F-for-Cl and Cl-for-F transfers) and non-concerted halogen exchange processes has been resolved more recently and the evidence is described later in the chapter. What is clear from this early work however, is the importance of aluminium and chromium(III) oxides as catalyst precursors. Fluorination of the surfaces of these oxides is slow (cf [12]) and although there are many references to alu-... 

Methane-14 was prepared (Ciranni and Guarino, 1966) from aluminium carbide and pure T2O. The crude CT4, specific activity of 116,500 Curies per mole, was immediately diluted with a large excess of CH4 and subjected to a rigorous purification, including a preparative gas-chromatographic separation over a special capillary column that allows (Bruner and Cartoni, 1965) the complete resolution of the four tritiated methanes, from CH3T to CT4. The final sample, whose isotopic purity is illustrated in Fig. 5, was further diluted with CH4 to a specific activity of 0-2 Curies per mole to carry out the decay experiments. Nefedov et al. (1968) used CT4 prepared by essentially the same procedure in their study of the reactions of methyl ions in hydroxylic compounds. 

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