Cell: Structure and Functions
A source contains two phosphorous radio nuclides and . Initially, 10% of the decays come from . How long one must wait until 90% to do so?
Solution: Let the number of atoms of be and atoms of be . The decay constants of two atoms be and respectively.
The initial activity of is times that of .
Therefore, we can write the decay constants as:
Let after time t the activity of be times that of
Now. Divide equation (ii) by (i) and taking the natural log of both sides we get
t comes out to be days