An unknown radioactive source is used as a static charge neutralizer in a dust generation system. You have been monitoring the activity of this source every month using a Geiger-Mueller Counter and have saved and plotted the resulting data in a anrasilaheet and a chart (halow) a. Based on these data, what is the balf-life of this radioisotope? b. Referring to Table 10-B (attached), which radioisotope does this half-life agree with? c. Now that you have identified the source, you want to know when it will need to be replaced. The manual for the static charge neutralizer indicates that it will function properly until the activity of the source falls below 100 mCi. Your last measurement showed that today (day 300 ) the activity was 221mCi. How many more months until the source has to be replaced? Table 10-B. Isotopes Commonly Available, Listed by Increasing Half-Life (Heprinted from Rediologica Heath Handbook, revised ed. danuary 1970. US. Dept of Health S Human Services. Aockile, MD.)