While I am grading the exam I noticed that I didn’t use the final (corrected) form of one problem and left a typo in that makes the problem unsolvable.
42. Iodine-131 is used to image thyroid tissue to determine the presence of thyroid cancer. Iodine-131 degrades through a beta followed by gamma mechanism. Determine the final product that is produced by the decay of iodine-131. If you can make a 2.0 mCi/ml solution of iodine-131 how much would have to be made 72 hours before the test (half-life: 8 hours) to make a solution with an activity of 7.4 x 10^3 Bq/ml for the test?
The last unit should have been in Bq, not Bq/ml. The question makes no sense at the end with the volume in the unit. However, much of the problem is solvable. So for the five points I will divide it as follows. One point for the decay equation. One point for the conversion of mCi/ml to Bq/ml or Bq/ml to mCi/ml. One point for the determination of the number of elapsed half-lives. If you made an effort at those you will get the last two points (even if you lost some in the previous three) for what would have been determining the amount of radiation needed and then the volume of stock needed. However, if you did not attempt the problem, or only trivially addressed it, you will not get the two final points.
My apologies, I pulled up an old draft when I printed it out.