the $210$Po source used in a physics laboratory is labeled as having an activity of $1\mathrm{.}0$ microCurie $($uCi$)$ on the date it was prepared. A student measures the radioactivity of this source with a Geiger counter and observes $1500$ counts per second. She notices that the source was prepared $72$ days before her lab. What fraction $($in $\%)$ of the decays is she observing with her apparatus? $1$ Ci$=3\mathrm{.}7*1010$ disintegrations per second half$-$life of $210$Po$=138\mathrm{.}376$ days