$(10$ points$)$ A crafty rat weighing $250g$ makes its way into the thermal column of the research reactor and is uniformly irradiated over its total body with thermal neutrons. The $)=(0\mathrm{.}534b$ in its blood is irradiated with thermal neutrons. How long must the rat remain in the thermal colum $n$ before the activity level in its blood reaches $0\mathrm{.}1Ci$ of $)=(15(h)?[$Assume a $50kg$ person has $200g$ of NaCl molecules in their blood, with $Na$ comprised of $100\%{?}^{23}Na$; assume the rat carries the same proportions$].$