Final answer:
The student's question appears to incorrectly mix unit-level security measures with physics problems regarding radioactivity. To clarify, for the physics aspect, it is necessary to understand the decay of radioactive isotopes and the efficiency of detection methods such as Geiger counters.
Step-by-step explanation:
The student's question pertains to the physical counting and monitoring of missiles and rockets as part of unit-level activities involving Security Risk Category I inventory checks. However, this question mixes security protocols with physics problems relating to radioactivity measurements, and it appears there may be some confusion in the context. For clarity, I can address the physics problems provided.
Understanding Radioactive Decay and Detection
Radioactivity measurements are essential in physics labs, particularly when dealing with radioactive isotopes like 210 Po. In the scenario described, where a source is labeled with an activity of 1.0 μCi and the student observes 1500 counts per minute 120 days after preparation, we can use the half-life of the isotope and its initial activity to determine the current activity and thus the fraction of decays the Geiger counter is observing.
For the second part of the physics problem, factors that contribute to only a fraction of decays being observed include the efficiency of the detector, the geometry of the setup, self-absorption of the radiation by the source, and the possibility of other types of decays that the detector is not sensitive to.