In a radioactive substance at t = 0, the number of atoms is 8 x 104. Its half-life period is 3 years. The number of atoms 1 x 10^4 will remain after the interval :
Correct answer: A. 9 years
- A. 9 years
- B. 8 years
- C. 6 years
- D. 24 years
Explanation
The number of atoms of a radioactive substance decreases by half after each half-life. So, after 3 years, the number of atoms will be 8 x 104 / 2 = 4 x 104. After another 3 years, the number of atoms will be 4 x 104 / 2 = 2 x 104. And after another 3 years, the number of atoms will be 2 x 104 / 2 = 1 x 104. Therefore, the interval after which 1 x 104 atoms will remain is 3 + 3 + 3 = 9 years.
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About Half-life and Rate of Decay
Half-life is the time required for half the unstable nuclei in a sample to decay, and it remains constant for a particular radioactive nuclide. Questions use the exponential decay law, decay constant, activity, remaining quantity and mean life. Radioactive decay is random for individual nuclei but predictable for large samples.
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