Suppose the daughter nucleus in a nuclear decay is itself radioactive - If and
denote the decay constant of daughter and mother nuclei and
and
the number of daughter and mother nuclei present at a time, then the number of daughter nuclei becomes constant then
The number of mother nuclei decaying in a short time interval at is .But death of a mother nucleus implies the birth of a daughter nucleus.
The number of daughter nuclei decaying in the same time interval is
the number of daughter nuclei will remain constant when