The activity of a freshly prepared radioactive sample is 1010 disintegrations per second whose mean life is 109 s. The mass of an atom of this radioisotope is 10–25 kg. The mass (in mg) of the radioactive sample is

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The activity of a freshly prepared radioactive sample is 10¹⁰ disintegrations per second whose mean life is 10⁹ s. The mass of an atom of this radioisotope is 10^–25 kg. The mass (in mg) of the radioactive sample is

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A = $λ$ N

$10^{10} = \frac{1}{10^{9}} N$

N = 10¹⁹

Mass of sample = 10¹⁹ × 10^–25 × 1 × 10⁶ =1 mg