9. A source has a half-life of 12 hours and an initial activity of 10 mci. After four days, what is its activity? 10. Calculate the percentage of activity remaining in a source after 10 halt lives. banil Iyrod bent two alhi esam simolit audi 1 1. a. A radionuclide decays 1% in one day. Calculate the half-life. b. A radionuclide decays 70% in one day. Calculate the half-life. 12. A sample of 10.0 mCi of a radioisotope decays 1.2 in a single day. a. What is the activity after one day? b. What is the activity after 30 days? mun lung 13. A sample of Cs-137 initially contains 1000 atoms. volwhata. What is the value of the decay constant for this isotope? b. How many Cs-137 atoms does the sample contain after two years? Use Equation (3.7). c. What is the change AN in the number of atoms over this time period? d. Verify the equation (AN/Ar) - -AN by substituting the values from parts a through c above, on both sides of the equation. 14. A radioactive source has a half-life of 74 days and an activity of 370 MBq. What was the activity 30 days ago? 15. A radioactive source has a half-life of 60 days. What is the relative activ. ity after one week? 16. A 13-Ci Ir-192 source is received on August 20. Regulatory requirements do not allow use of the source until its activity is 12 Ci or less. On what date will the source reach this activity? 17. A patient had a 25-mCi I-125 permanent seed implant three years ago. muhl What is the activity now? 18. For a prostate "seed" implant, I-125 seeds with an activity of 0.350 mCi are needed on the day of the implant. The seeds are to be delivered one week prior to the implant. What activity should the seeds have on the day of delivery? 19, Describe the beta decay process. Explain the energy spectrum of the emit- ted beta ray's. Write down the general equation for B' and B decay pro- cesses, and give one example for each case, A 20. Describe the processes of electron capture and internal conversion