CHAPTER 24 Nuclear Energy I. Radioactivity (p.674-683) 1 1

A. Definitions Radioactivity emission of high-energy radiation from the nucleus of an atom Nuclide nucleus of an isotope Transmutation process of changing one element into another via nuclear decay

B. Nuclear Decay Why nuclides decay… to obtain a stable ratio of neutrons to protons Stable Unstable (radioactive)

C. Half-life Half-life (t½) time it takes for half of the nuclides in a sample to decay Example Half-lives polonium-194 0.7 seconds lead-212 10.6 hours iodine-131 8.04 days carbon-14 5,370 years uranium-238 4.5 billion years

D. Half-life total time = 30 hours number of half-lives = 2 How much of a 20-g sample of sodium-24 would remain after decaying for 30 hours? Sodium-24 has a half-life of 15 hours. GIVEN: total time = 30 hours t1/2 = 15 hours original mass = 20 g WORK: number of half-lives = 2 20 g ÷ 2 = 10 g (1 half-life) 10 g ÷ 2 = 5 g (2 half-lives) 5 g of 24Na would remain.