Naturally occurring radioactive nuclides half-lives

The values of half-lives of naturally occurring radioactive nuclides vary enormously, e.g. 4.5 x 10 yr for and 1.6xl0 s for sjPo. Table 2.1 lists half-life data for nuclides involved in the decay series in Figure 2.3. 

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. 

All elements beyond bismuth in the Periodic Table are radioactive, most of these having several isotopes (or nuclides), each with a characteristic half-life. A small number of elements of low atomic number (K, Rb, Sm, Lu, Re, and perhaps La and H) each have one naturally occurring radioisotope also. In addition, over 700 radioisotopes have been made artificially (p. 466). 

There are 280 naturally occurring nuclides that make up the 83 stable and long-lived elements. These are all the elements up to Bi with Z = 83, except for unstable Tc (Z = 43) and Pm (Z = 61) that only have short-lived isotopes, but the long-lived Th and U bring the total back to 83. Here long-lived or short-lived is with respect to the half-life of an isotope against radioactive decay and the age of the solar system. Long-lived means then an element is still present in measurable quantities since the solar system formed 4.6 Gyr ago, and radioactive isotopes with half-lives above 0.6 Gyr usually qualify... 

During the formation of the Earth, 4.65 billion years ago, along with the stable nuclides, several radionuclides were formed. Those that were radioactive with a half-life too short with respect to the formation of the Earth obviously disappeared. On the other hand, those with half-lives of the same order of magnitude or greater than that of the formation of Earth are mainly responsible for the natural radioactivity of the Earth s crust materials (i.e., ice, river, sea and ocean waters, minerals, ores, rocks, and soils). Today, over 60 radionuclides occur in the environment, and they can be grouped into three main categories ... 

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... 

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