An ancient club is found that contains 140 g of pure carbon and has an activity of 4.5 decays per second. Determine its age assuming that in living trees the ratio of atoms is about . Note that the half life of carbon-14 is 5700 years and the Avogadro number is . years 2. One of the many isotopes used in cancer treatment is , with a half-life of 2.70 d. Determine the mass of this isotope that is required to give an activity of 205 Ci. mg 3. The radioactive isotope ( Mo) has a half-life of 2.75 days. A sample containing this isotope has an initial activity at (t