Naturally occurring radioactive nuclides abundance

FlC- 1-2, The three naturally occurring radioactive decay series and the man-made neptunium series. Although (which is the parent to the actinium series) and (which is the parent to the thorium series) have been discovered in nature, die decay series shown here begin with the most abundant Icmg-Uved nuclides. 

Rhenium, atomic wt 186.2, occurs in nature as two nuclides 185Re [14391-28-7], mass 184.9530, in 37.500% abundance and 187Re [14391-29-8], mass 186.9560, in 62.500% abundance. The latter isotope is radioactive, emitting very low energy radiation and having a half-life estimated at 4.3 ( 0.5) x 1010 yr. The radioactive decay of this isotope has been used to date accurately the time of Earth s formation. 

For a nuclear weapon hurst in air. all materials in the fireball are vaporized. Condensation of fission products and other bomb materials is then governed by the saturation vapor pressures of the most abundant constituents. Primary debris can combine w ilh naturally-occurring aerosols, and almost all of (he fallout becomes tropospheric or stratospheric. If the weapon detonation takes place within a few hundred Icet of (either above or below) a land or water surface, large quaniilies of surface materials are drawn up or thrown into the air above Ihe place ol detonation. Condensation of radioactive nuclides in this material then leads in considerable quantities of local fallout, but some of the radioactivity still goes into tropospheric and stratospheric fallout. If the hurst occurs sufficiently fur underground, the surface is not bruken and no fallout results. 

Different isotopes have different natural abundances. For example, 99.3% of naturally occurring uranium is uranium-238, 0.7% is uranium-235, and only a trace is uranium-234. Different nuclei also have different stabilities. Indeed, the nuclear properties of an atom depend on the number of protons and neutrons in its nucleus. Recall that a nuclide is a nucleus with a specified number of protons and neutrons. (Section 2.3) Nuclei that are radioactive are called radionuclides, and atoms containing these nuclei are called radioisotopes. 

The natural radioactive decay scheme of Figure 25-2 suggests the eventual fate of all in nafure—conversion to lead. Naturally occurring uranium minerals always have associated with them some nonradioactive lead formed by radioactive decay. From the mass ratio of Pb to 92U in such a mineral, it is possible to estimate the age of the igneous rock containing the mineral. The age of fhe rock refers to the time elapsed since molten magma solidified to form the rock. One assumption of this method is that the initial radioactive nuclide, the final sfable nuclides, and all the products of a decay series remain in the rock. Another assumption is that any lead present in the rock initially consisted of the several isotopes of lead in their present, naturally occurring abundances. 

The amount of a nuclide (stable or radioactive) relative to other nuclides of the same element in a given sample. The natural abundance is the abundance of a nuclide as it occurs naturally. For instance, chlorine has two stable isotopes of masses... 

All Isotopes of the elements of the Pt group which are stable against radioactive decay were found in nature. In the case of Os and Pt even the two radioactive Isotopes Os and do occur in nature because they did not decay out due to their long half-life. The abundance in the natural elements of these two primordial nuclides as well as of... 

---