Radioactive decay. See Radioactivity

Elements slightly heavier than uranium, produced by radioactive decay (see later), are found in tiny amounts in natural uranium ores. Plutonium (element 94) has also been found in nature, a product of the element-forming processes that happen in dying stars. So it is a tricky matter to put a precise number on the natural elements. 

It designates a type of radioactive decay. See beta particle. 

For the well-mixed reservoirs, a conservation equation is written in which gain of 14C by inflow to the box (atmosphere or surface ocean) is balanced by the outflow to other boxes plus radioactive decay (see Section 2.8) of the tracer during its time in the reservoir. For the deep ocean, conservation is described by a partial differential advection-diffusion equation. The... 

Because strontium is an element, its atoms do not degrade by environmental processes such as hydrolysis or biodegradation. However, radioactive strontium will be subject to radioactive decay and transformation to other elements. Eventually, all of the radioactive strontium will be transformed into stable zirconium by the process of radioactive decay (see Section 4.2) ... 

Astatine is the heaviest member of group 17 and is known only in the form of radioactive isotopes, all of which have short half-lives. The longest lived isotope is At (fi = 8.1 h). Several isotopes are present naturally as transient products of the decay of uranium and thorium minerals At is formed from the 3-decay of Po, but the path competes with decay to Pb (the dominant decay, see Figure 2.3). Other isotopes are artificially prepared, e.g. "At (an a-... 

The lanthanoids resemble each other much more closely than do the members of a row of t/-block metals. The chemistry of the actinoids is more complicated, and in addition, only Th and U have naturally occurring isotopes. Studies of the transuranium elements (those with Z > 92) require specialized techniques. The occurrence of artihcial isotopes among the /-block elements can be seen from Appendix 5 all the actinoids are unstable with respect to radioactive decay (see Section 24.9), although the half-lives of the most abundant isotopes of thorium and uranium ( Th and t = 1.4 x lO and 4.5 x 10 yr respectively) are... 

Such a sequence is known as series or consecutive reactions. In this case, B is known as an intermediate because it is not the final product. A similar situation is very common in nuclear chemistry where a nuclide decays to a daughter nuclide that is also radioactive and undergoes decay (see Chapter 9). For simpficity, only the case of first-order reactions will be discussed. 

Another characteristic time parameter of radioactive decay is the mean life r, which is the expected value of the y (1, A) exponential distribution associated with radioactive decay (see Chap. 9 in this Volume) ... 

PARENT A radionuclide that transforms to another by radioactive decay. See daughter. 

The time taken for the concentration of reactant to he halved during a chemical reaction is called the half-life. Identical kinetic behaviour is exhibited by substances undergoing radioactive decay (see Chapter 2), with the exception that this physical process is unaffected by changes in temperature. For a reaction that has an overall order of 1, the half-life is constant and is independent of the initial concentration of the reactants (see Figure 16.7). 

The best way to manage hazardous waste disposal to the geosphere is to render all wastes non-hazardous before disposal. Unlike radioactive wastes that eventually decay (see later in this section), some hazardous chemical wastes never degrade and no secure landfill can be assumed to be secure forever. Organic wastes, such as refractory organochlorine compounds, should be destroyed by thermal process, and toxic heavy metals should be separated and recycled. 

The parameter is obtained from the compartment-specific half-life or residence times that apply to bulk removal by processes such as photolysis, hydrolysis, oxi-dation/reduction, microbial transformations, and radioactive decay (see Section 8.5). This parameter is estimated as 0.693/ri/2, where ri/2 is the half-time for a given removal process. 

Cold cathode A non-thermoelectron-emitting cathode that emits electrons, usually by secondary electron emission, under ion bombardment or by radioactive decay. See also Field emission. 

Radiocarbon dating (43) has probably gained the widest general recognition (see Radioisotopes). Developed in the late 1940s, it depends on the formation of the radioactive isotope and its decay, with a half-life of 5730 yr. After forms in the upper stratosphere through nuclear reactions of... 

Argon-40 [7440-37-1] is created by the decay of potassium-40. The various isotopes of radon, all having short half-Hves, are formed by the radioactive decay of radium, actinium, and thorium. Krypton and xenon are products of uranium and plutonium fission, and appreciable quantities of both are evolved during the reprocessing of spent fuel elements from nuclear reactors (qv) (see Radioactive tracers). 

Neutron-rich lanthanide isotopes occur in the fission of uranium or plutonium and ate separated during the reprocessing of nuclear fuel wastes (see Nuclearreactors). Lanthanide isotopes can be produced by neutron bombardment, by radioactive decay of neighboring atoms, and by nuclear reactions in accelerators where the rate earths ate bombarded with charged particles. The rare-earth content of solid samples can be determined by neutron... 

Lead, atomic number 82, is a member of Group 14 (IVA) of the Periodic Table. Ordinary lead is bluish grey and is a mixture of isotopes of mass number 204 (15%), 206 (23.6%), 207 (22.6%), and 208 (52.3%). The average atomic weight of lead from different origins may vary as much as 0.04 units. The stable isotopes are products of decay of three naturally radioactive elements (see Radioactivity, natural) comes from the uranium series (see Uraniumand... 

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