The half-life of a radioactive substance against α-decay is 1.2 x 107 s. What is the decay rate for 4 x 1015 atoms of the substance?
4.6 x 1012 atoms/s
2.3 x 1011 atoms/s
4.6 x 1010 atoms/s
2.3 x 108 atoms/s
dNdt=λN⇒dNdt=0.693T1/2x N 0.6931.2 x 107 x 4 x 1015=2.3 x 108 atoms/sec