6000 atoms are in an excited state that has a lifetime 14.43 ns. a) At what time t1/2 have half the atoms decayed? b) How many atoms have decayed at t = 40 ns? c) Draw a graph of Nexc as a function of time. Show in the graph the lifetime, 1t1/2, 2t1/2, 3t1/2 and 4t1/2.