Nuclides Significant figures

It takes 3 half-lives for a radioactive nuclide to decay to Vi of its original amount (Vi xViX Vi). Therefore, it will take 103.5 hours (104 hours to three significant figures) for krypton-79 to decrease to Vs of what was originally there. 

Gamma spectrometry of materials containing these nuclides can only be effectively done with a detailed understanding of the decay chains of the nuclides involved. Figures 16.1,16.2 and 16.3 show the three decay series. These are incomplete in that they do not show a number of minor branches. Those, however, are of no practical significant to gamma spectrometry. 

Bainbridge and Jordan determined the mass of nuclides to six significant figures, the first accurate mass application. 

There are three significant features in Figure 4. First, the various sorption mechanisms affect each nuclide differently. Second, the amount of each radionuclide that is exchangeable or reversibly sorbed is less than 50% for all nuclides tested. In 28 days, more than 50% of the sorbed radionuclides have undergone phase transformation or reacted with oxyhydroxides to form nonexchangeable phases. Third, for a given radionuclide, the... 

Table 13.1 shows the environmentally significant radioisotopes of metals and metalloids considered in this chapter. Figure 13.1 shows some of the fluxes of radioactive nuclides in the environment. 

Ra and Ra are two other members of the U-Th series (Figure 1) for which dissolved concentration data are available for several rivers, these show that they are present at levels of 0.1 d.p.m. 1 . The available data show that there are significant differences between the abundances of U, Ra isotopes and Th in the host rocks and in river waters. The various physicochemical processes occurring during the mobilization and transport of these nuclides contribute to these differences. 

Diffusion out of sediments forms a significant input for Ra isotopes, Ac and Rn into overlying water. All these nuclides are produced in sediments through a-decay (Figure 1). The recoil associated with their production enhances their mobility from sediments to pore waters from where they diffuse to overlying sea water. Their diffusive fluxes depend on the nature of sediments, their accumulation rates, and the parent concentrations in them. is another isotope for which supply through diffusion from sediments may be important for its oceanic budget. 

Other neutron-induced reactions will normally involve energetic or fast neutrons, where the extra kinetic energy is needed to knock out extra particles. Common reactions are (n, p), (n, a) and (n, 2n), and Figure 1.28 shows these transformations on the Z against N nuclide chart format. The quantity of radioactivity formed by these reactions is often small because of relatively low fluxes of fast neutrons and small cross-sections. However, reactor operators and persons involved in reactor decommissioning wiU be aware of the significant amounts of activity that can be formed by certain reactions, such as, Fe(n, p) Mn, Ni(n, p) Co and Al (n, a) Na. The likelihood of the production of aU these radionuclides can again be followed on the nuclide chart. 

Seven of the twelve nuclides decay by electron capture and, as we saw in Section 1.2.3, every decay will be accompanied by X-rays characteristic of the daughter atom. That means that we can expect summing between the gamma-rays and the X-rays. As Table 8.2 indicates, y-X sum peaks from Co, Ce and are very evident (see Figures 8.7(b) and 8.7(c)). Although similar summing in Am and Zn can be detected, it was barely significant in the particular spectrum analysed. 

Not aU of the nuclides in the series emit significant gamma radiation and, of those, only the six underlined in Figure 16.1 can be measured with ease. It is common to measure those nuclides and use the results to achieve a best estimate of the parent activity. In doing so, agreement between the early members of the chain, Th, Pa and 22 Ra, and the later members, i Pb, 2i Bi and 2 °Pb (but see below), confirms that the series is in decay-equilibrium. 

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