A radioactive isotope has a half-life of 3 years. A sample records a count rate of 100 counts/min on a detector. Which calculation is used to predict the count rate after 12 years?
- A$100 \times \frac{1}{2} \times \frac{1}{2} \times \frac{1}{2} \times \frac{1}{2}$
- B$100 \times \frac{1}{2} \times \frac{1}{2} \times \frac{1}{2}$
- C$100 \times \frac{3}{12}$
- D$100 \times \frac{12}{3} \times \frac{1}{2}$