Solve: (a) (b) The mass of radium is the number of nuclei times the mass of each one. (c) There are Reflect: The activity is directly proportional to the mass of the radioactive nuclei in the sample. The mass in part (c) is about ten times that in part (b), and the activity is about a factor of ten times larger. 30.20. Set Up: The activity of carbon in the atmosphere is 0.255 Bq per gram of carbon. The half-life of is 5730 yr. Solve: The activity of a present-day sample with 55.0 g of carbon is and so the age of the sample is 30.21. Set Up: One-half of the sample decays in a time of Solve: (a) (b) This exponent is too large for most hand-held calculators. But so 30.22. Set Up: The mass of a single nucleus is Solve: (a) (b) (c) 30.23. Set Up: and is the SI unit of absorbed dose. Sv is the SI unit for equivalent dose. Rem is the equivalent dose when the absorbed dose is in rad. For x rays, For protons, Solve: (a) 5.0 Gy, 500 rad. so equivalent dose. 5.0 Sv and 500 rem. (b)
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