Professor Curie is using the radioactive isotope Francium-223 in her research. This isotope has a half-life of 22 minutes, which means that every 22 minutes the sample has half the radioactivity it did in the previous interval. If Professor Curie has 15 grams of Francium-223, which explicit formula describes how the isotope decays? A. an=22(0.5)^15-1
B. an=22(0.5)^n-1
C. an=15(0.5)^n-1
D. an=15(22)^n-1