(b) 76.0 min is one so is proportional to N , so the activity is (c) 152 min is one after the time in part (b), so and the activity is 30.15. Set Up: The mass of a single nucleus is Solve: Reflect: The shorter the half-life the greater the decay rate for the same number of radioactive nuclei. 30.16. Set Up: The mass of a single nucleus is Solve: 30.17. Set Up: The decay rate decreases by a factor of 2 in a time of one half-life. Solve: (a) 24 d is so the activity is (b) The activity is proportional to the number of radioactive nuclei, so the percent is (c) The nucleus is produced. Reflect: Both the activity and the number of radioactive nuclei present decrease by a factor of 2 in one half-life. 30.18. Set Up: The activity is The mass of one is approximately Solve: (a) (b) The mass m of uranium is the number of nuclei times the mass of each one. (c) 30.19. Set Up: The activity is The mass of one nucleus is approximately 1 Ci 5 3.70 3 10 10 decays / s. 226 m p . 226
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