NEET-XII-Physics
13: Nuclei
- #25A source contains two phosphorous radio nuclides
(T1/2 = 14.3d) and 
(T1/2 = 25.3d). Initially, 10% of the decays come from. How long one must wait until 90% do so?
Ans : Half life of, T1/2 = 14.3 days
Half life of, T’1/2 = 25.3 days
nucleus decay is 10% of the total amount of decay.
The source has initially 10% ofnucleus and 90% of nucleus.
Suppose after t days, the source has 10% ofnucleus and 90% of nucleus.
Initially:
Number ofnucleus = N
Number ofnucleus = 9 N
Finally:
Number of
Number of
Fornucleus, we can write the number ratio as:
For, we can write the number ratio as:
On dividing equation (1) by equation (2), we get:
Hence, it will take about 208.5 days for 90% decay of
.