4. lodine - 131 is a radioactive isotope with a half- life of 8 days. A cloud of vapour containing this isotope escapes from a factory and a three mile radius from the factory is deemed unsafe to enter until the radiation count is 125 counts per second or below. If the initial count is 128,000 counts per second, how many days will it take before it becomes safe to enter the zone? a) 32 days b) 98 days c) 22 days d) 88 days e) 54 days