A student measures the half-life of a radioactive isotope. Over a five-minute interval, the student uses a detector and draws a graph to show how the count rate on the detector changes with time. The count rate from background radiation is $30$ counts per minute. What is the half-life of this isotope?
- A$0.30$ minutes
- B$1.2$ minutes
- C$1.5$ minutes
- D$5.0$ minutes