90 A small building has become accidentally contaminated with radioactivity. The longest-lived material in the building is strontium-90. (Sr has an atomic mass 89.9077 u, and its half-life is 29.1 yr). It is particularly dangerous because it substitutes for calcium in bones. Assume that the building initially contained 5 kg of this substance uniformly distributed throughout the building and that the safe level is defined as less than 10 decays/min (to be small in comparison to background radiation). How long will the building be unsafe? Given: u=1.66x10-27 kg.

Thorium  22890Th produces a daughter nucleus that is radioactive. The daughter, in turn, produces its own radioactive daughter, and so on. This process continues until bismuth 21883Bi is reached. What are (a) the total number Nα of α particles and (b) the total number Nβ of β- particles that are generated in this series of radioactive decays?

58. . Radiation treatment of prostate cancer. In many cases, BIO prostate cancer is treated by implanting 60 to 100 small seeds of radioactive material into the tumor. The energy released from the decays kills the tumor. One isotope that is used (there are others) is palladium (10°Pd), with a half-life of 17 days. If a typical grain contains 0.250 g of 10°Pd, (a) what is its initial activity rate in Bq, and (b) what is the rate 68 days later?

9. A rock that contains 1.2x10-12 mol of 232Th (t1/2 = 1.4x1010 yr) has 4.2x105 fission tracks, each track representing the fission of one atom of 232Th. How old is the rock?

Time 0 t₁2 20₁2 3₁/12 Number of nuclides, N x 10³ 1000 750 500 90/2 10/₁2 250 125 0 12 212 312 412 512 612 7h2 8h2 9h12 10/2 Time in multiples of t₁/2 The figure shows a typical radioactive decay (amount of undecayed nucleus (N) vs. time (t)) from a heavy nucleus. Such a decay may be best expressed by an equation like : ON = N₂ (xt) ON=N₂/λt -λt ON = N₂e N = N₂ e-1/At N 1,000,000 500,000 250,000 125,000 62,500 31,250 15,625 7,813 3,906 1,953 977 412 5/₁/2 61₁2 7h2 81/2

If 88 (atomic number)  228 (atomic mass) ?? is produced, determine the parent isotope for each of the following types of decay and justify  your answer. a) alpha decay b) beta negative decay c) beta positive decay

11. Radium-226, 226Ra, undergoes an alpha decay. The current sample of Radium-226 has an initial activity of 5.50 × 101º Bq. (a) Identify the daughter nucleus by name, nucleon number, atomic number and neutron number. (b) What is the decay constant? (c) How many radioactive nuclei were initially present in the sample? (d) How long will it take the sample to reach an activity of 5.00 x 1010 Bq?