The half-life of Th(227) is 18.72 days. It decays by alfa emission to Ra(223), an alfa emitter whose half-life is 11.43 days. A particular sample contains 10^6 [10E(+6)] atoms of Th(227) and no Ra(223) at time t=0.
a) How many atoms of each type will be in the sample at t=15 days?
b) At what time will the number of atoms of each type be equal?