Q18 of 26 Page 1

(i) Define ‘activity’ of a radioactive substance.

(ii) Two different radioactive elements with half-lives T1 and T2 have N1 and N2 undecayed atoms respectively present at a given instant. Derive an expression for the ratio of their activities at this instant in terms of N1 and N2


The number of disintegrations of a given sample per second is known as the activity of the radioactive substance.


Mathematical expression of activity is given by,



(ii) Given:


Number of undecayed atoms are N1 and N2.


Half-life period, T1 and T2.


Calculation:


Number of first undecayed atoms is given by,



Activity is given by,



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