In a vacuum, a radioactive source emits a beam of $\alpha$-particles. The mean current due to the $\alpha$-particles in the beam is $1.5 \times 10^{-9}\,\text{A}$. The beam strikes a metal target. What is the mean number of $\alpha$-particles reaching the metal target in a time of $3.0\,\text{s}$?
- A$4.7 \times 10^{9}$
- B$9.4 \times 10^{9}$
- C$1.4 \times 10^{10}$
- D$2.8 \times 10^{10}$