Naturally occurring radioactive nuclides

Analyses of this type are correct only if all of the product nuclide comes from radioactive decay. This is not known with certainty, but when age estimates using different pairs of nuclides give the same age and samples from different locations also agree, the age estimate is likely to be accurate. Note also that 3.8 X 10 years agrees with the qualitative limits derived from naturally occurring radioactive nuclides. 

Objective 16 Many of the naturally-occurring radioactive nuclides have relatively short 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. 

The chain of radioactive decay that begins with continues through a number of steps of a and j8 emission until it eventually terminates with a stable isotope of lead— 82 1. The entire scheme is outlin in Figure 25-2. All naturally occurring radioactive nuclides of high atomic number belong to one of three radioactive decay series the uranium series just described, the thorium series, or the actinium series. (The actinium series actually begins with uranium-235, which was once called actino-uranium.)... 

A number of basic questions have probably occurred to you as nuclear decay processes have been described Why do some radioactive nuclei decay by a emission, some by j8 emission, and so on Why do the lighter elements have so few naturally occurring radioactive nuclides, whereas all those of the heavier elements seem to be radioactive ... 

All naturally occurring radioactive nuclides of high atomic number are members of a radioactive decay series that originates with a long-lived isotope of high atomic number and terminates with a stable isotope, such as o Pb (Fig. 25-2). 

Mass spectrometric techniques play a dominant role for the determination of transuranium elements in bulk samples as well as in microparticles. The radioactive element most frequently investigated by inorganic mass spectrometry is uranium. The determination of the concentrations and the precise isotopic analysis of naturally occurring radioactive elements (e.g. Th and the decay nuclides) by inorganic mass spectrometry as terrestrial... 

There are essentially three sources of radioactive elements. Primordial nuclides are radioactive elements whose half-lives are comparable to the age of our solar system and were present at the formation of Earth. These nuclides are generally referred to as naturally occurring radioactivity and are derived from the radioactive decay of thorium and uranium. Cosmogenic nuclides are atoms that are constantly being synthesized from the bombardment of planetary surfaces by cosmic particles (primarily protons ejected from the Sun), and are also considered natural in their origin. The third source of radioactive nuclides is termed anthropogenic and results from human activity in the production of nuclear power, nuclear weapons, or through the use of particle accelerators. 

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. 

NORM Naturally Occurring Radioactive Material. NORM includes some of the primordial nuclides and their daughters and certain nuclides continuously created in the environment. Contrast anthropogenic radiotmclides. 

The demands for assessing the potential impact of radionuclides produced by military and nuclear power supply applications on environmental quality and human and the desire to remediate radionuclide-contaminated site have triggered an intensive and wide range of research activities. Soil chemical reactions are critical to both environment and human health and to successful remediation. This chapter s aim is to briefly describes the physical and chemical characteristics of the most important radioactive nuclides likely to be found in soils. The primary sources of these radionuclides include the fallout from atmospheric weapon tests, release from fuel processes facilities, nuclear material storage facilities, biomedical applications, and, of course, naturally-occurring radioactive elements. The forms and interactions of the radionuclides in soil environment are subsequently discussed. 

Elements with radioactive nuclides amongst their naturally occurring isotopes have a built-in time variation of the relative concentration of their isotopes and hence a continually... 

C22-0023. Potassium-40 is a radioactive nuclide that occurs naturally. This nuclide emits 3 particles with the... 

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. 

Activation analysis is based on the production of radioactive nuclides by means of induced nuclear reactions on naturally occurring isotopes of the element to be determined in the sample. Although irradiations with charged particles and photons have been used in special cases, irradiation with reactor thermal neutrons or 14 MeV neutrons produced by Cockcroft-Walton type accelerators are most commonly used because of their availability and their high probability of nuclear reaction (cross section). The fundamental equation of activation analysis is given below ... 

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). 

H, C, P, and l. The word isotope comes from Greek, meaning at the same place , a useful way to remember that all isotopes of an element are in the same place in the Periodic Table of elements. While not quite correct, often the words isotope and nuclide are used interchangeably. Thus, radioisotopes may be termed radionuclides. The later refers to an atom with an unstable nucleus that undergoes radioactive decay, and these may be naturally occurring or artificially produced. 

---