1. Chapter 21

2. 1. What is a nuclear reaction? 2. What are nucleons? Nuclides? Radionuclides? Radioisotopes? 3. What are the three main types of radiation?  List their properties (Table 21.1) 4. List the common particles and symbols in radioactive decay (Table 21.2)

6. Radioactive Decay  Two possibilities: 1. Nucleus can spontaneously decay 2. Nucleus can change identity if it is struck by a neutron or by another nucleus  Nuclear transmutation

7.  Some radioisotopes, such as uranium-238, are found in nature, although they are not stable.  Other radioisotopes do not exist in nature, even though they can be synthesized in nuclear reactions.  Different nuclei undergo radioactive decay at different rates

8. Rates of Radioactive Decay  Radioactive decay is a first-order kinetic process  Half-life is the time required for half of any given quantity of a substance to react  Rate = kN where N = number of radioactive nuclei and k = decay constant

9. Rates of Radioactive Decay  The rate at which a sample decays is called its activity  Expressed as the number of disintegrations observed per unit time.  The Becquerel (Bq): the SI unit for expressing activity of a particular radiation source  The curie (Ci) is the rate of decay of one gram of radium

10. Calculating the Age of a Mineral  How much time is required for a 6.25-mg sample of chromium-51 to decay to 0.75mg if it has a half-life of 27.8 days?  A rock contains 0.257mg of lead-206 for every milligram of uranium-238. The half-life for the decay of uranium-238 to lead-206 is 4.5x10 9 yr. How old is the rock?

11. Calculating the Age of a Mineral  It takes 5.2 minutes for a 1.00-g sample of francium-210 to decay to 0.250g. What is the half-life of francium-210?