Radioactive decay sulfides

The experiment conducted by Rutherford and his co-workers involved bombarding gold foil with alpha particles, which are doubly charged helium atoms. The apparatus used in their experiment is shown in Figure 14-9. The alpha particles are produced by the radioactive decay of radium, and a narrow beam of these particles emerges from a deep hole in a block of lead. The beam of particles is directed at a thin metal foil, approximately 10,000 atoms thick. The alpha particles are delected by the light they produce when they collide with scintilltaion screens, which are zinc sulfide-covered plates much like the front of the picture tube in a television set. The screen... 

The planets nearest the Sun have a high-temperature surface while those further away have a low temperature. The temperature depends on the closeness to the Sun, but it also depends on the chemical composition and zone structures of the individual planets and their sizes. In this respect Earth is a somewhat peculiar planet, we do not know whether it is unique or not in that its core has remained very hot, mainly due to gravitic compression and radioactive decay of some unstable isotopes, and loss of core heat has been restricted by a poorly conducting mainly oxide mantle. This heat still contributes very considerably to the overall temperature of the Earth s surface. The hot core, some of it solid, is composed of metals, mainly iron, while the mantle is largely of molten oxidic rocks until the thin surface of solid rocks of many different compositions, such as silicates, sulfides and carbonates, occurs. This is usually called the crust, below the oceans, and forms the continents of today. Water and the atmosphere are reached in further outward succession. We shall describe the relevant chemistry in more detail later here, we are concerned first with the temperature gradient from the interior to the surface (Figure 1.2). The Earth s surface, i.e. the crust, the sea and the atmosphere, is of... 

The combination of radiolabeled sulfide and the bimane-HPLC method is particularly powerful because one of the main obstacles to the use of labeled sulfide is, that aside from radioactive decay, the compound is subject to rapid oxidation in the presence of air. The breakdown products of chemical sulfide oxidation are the same as those of biological oxidation. Previously it has been impossible to check routinely the purity of the purchased isotope and its subsequent purity during a series of experiments. It is our experience that newly purchased sodium sulfide sometimes contains up to 10% thiosulfate as well as traces of sulfite and sulfate (Figure 2), and that the sulfide once hydrated readily oxidizes if stored in a normal refrigerator. 

The advent of laser ablation MC-ICP-MS technology allows the rapid in situ determination of the stable isotope ratios of heavy metals commonly found in sulfide ore deposits (e.g., Cu, Zn, Fe, Sb, Ag) providing important information on the source, transport, and depositional mechanisms of these metals. Pb, Pb, and Pb are formed as the end product of radioactive decay and the isotopic variability of lead results because the elements from which the isotopes form were not evenly distributed in ore bodies. Hence, the analysis of stable lead isotopes in annually laminated lake-sediments is a useful method to study lead pollution history as the relative contribution of pollution and natural lead in sediment samples can be calculated. The analysis of lead isotopes by SIMS has also been used to identify the geographical origin of bullets. 

Dating sulfide minerals is complicated because they lack radioactive elements such as uranium, thorium, and rubidium. However, some contain potassium, e.g., the mineral rasvumite, KFe2S3. Samples of this mineral were collected from an alkali-rich igneous rock at Coyote Peak near Areata, northern CaKfomia, and they gave a date of 26.5 0.5 Ma, while associated phlogopite mica yielded a total release date from Ar/ Ar measurements of 28.3 0.4 Ma. This confirms that potassium-bearing sulfide minerals can be dated on the basis of the radioactive decay scheme... 

Another instrument often used to detect levels of radioactivity is a scintillation counter, which takes advantage of the fact that certain substances, such as zinc sulfide, give off light when they are struck by high-energy radiation. A photocell senses the flashes of light that occur as the radiation strikes and thus measures the number of decay events per unit time. 

Impurities sensitize some azides. For example, Gray and Waddington [18] introduced thallous sulfide into thallous azide and found that the initiation temperature was lowered. For pure lead azide the initiation temperature was 763°K whereas for the impure lead azide it was 693°K. Similarly, lead azide crystals containing 1% of carbon particles of size less than 1 /im initiate at temperatures below that of the pure lead azide [19]. An interesting method for introducing small quantities of impurities into silver azide was used by Deb et al. [20]. They prepared silver azide by using radioactive Ag, which decays by j3-emission into Cd. This method allowed 10" % of impurity to be introduced. It is important that even such small quantities affected not only the sensitivity but also the... 

The beta decay scheme of rhenium-187 to osmium-187 maybe applied to the study of sulfide minerals of molybdenum and osmium-rich minerals such as iridosmine. Together with rubidium/strontium, samarium/neodymium, lutetium/hafnium, and uranium/lead methods, it has been used to examine mantle differentiation and the accretion of continental crust. In molybdenites, rhenium concentrations vary from a few ppm to as much as 1.88%. The element has two naturally occurring isotopes, and these are the stable rhenium-185 with a relative abundance of 37.398% and the radioactive rhenium-187 with a relative abundance of62.602%. This decays as follows ... 

Common lead (i.e., lead that had long lost any association with the decay series discussed above) is found in many minerals such as galena (lead sulfide) and cerussite (lead carbonate), which are constituents of ore-forming bodies. Also, it occurs as a trace element in minerals where associated uranium and thorium contents are low as well as in rock-forming minerals such as feldspars. The atomic weight of common lead is less than that of lead associated with uranium. The difference is due to the increased presence of radiogenic lead-206 in the latter. Common lead, namely, contains isotopes of the element with mass numbers 204,206,207, and 208. Lead-204 is not the decay product of a radioactive series, but the other three derive from the radioactive series initiated by uranium-238, uranium-235, and thorium-232, respectively. The relevant atom number ratios are denoted as follows ... 

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