The Kinetics of Radioactive Decay and Radiometric Dating

A FIGURE 19.8 Gelger-Muller Counter When ionizing radiation passes through the argon-fiUed chamber, it ionizes the argon atoms, giving rise to a brief, tiny pulse of electrical current that is transduced onto a meter or into an audible chck. 

Radioactivity is a natural component of our environment. The ground beneath you most likely contains radioactive atoms that emit radiation. The food you eat contains a residual quantity of radioactive atoms that are absorbed into your body fluids and incorporated into tissues. Small amounts of radiation from space make it through our atmosphere to constantly bombard Earth. Humans and other living organisms have evolved in this environment and have adapted to survive in it. 

One reason for the radioactivity in our environment is the instabihty of all atomic nuclei beyond atomic number 83 (bismuth). Every element with more than 83 protons in its nucleus is unstable and therefore radioactive. In addition, some isotopes of elements with fewer than 83 protons are also unstable and radioactive. Radioactive nuclides persist in our environment because new ones are constantly being formed, and because many of the existing ones decay away only very slowly. 

All radioactive nuclei decay via first-order kinetics, so the rate of decay in a particular sample is directly proportional to the number of nuclei present as indicated in the equation  

The time it takes for one-half of the parent nuchdes in a radioactive sample to decay to the daughter nuclides is the half-life, and is identical to the concept of half-life for chemical reactions that we discussed in Chapter 13. Thus, the relationship between the half-life of a nuclide and its rate constant is given by the same expression (Equation 13.19) that we derived for a first-order reaction in Section 13.4  

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