The half-life of a radioactive isotope is 8 days. A detector placed near a sample of this isotope records a count rate of 200 counts per minute. In the absence of the source, the background count is 20 counts per minute. What is the count rate from the source after 8 days?
- A80 counts per minute
- B90 counts per minute
- C100 counts per minute
- D110 counts per minute