Cobalt-57 is radioactive, emitting β particles. The half-life for this is 270 days. If 100 mg of this is kept in an open container, the mass of Cobalt-57 after 540 days will be:
Correct answer: C. 25 mg
- A. 50 mg
- B. 50/√2 mg
- C. 25 mg
- D. Zero
Explanation
Half life = 270 days Total time given = 540 days Number of half-lives => n = 540 / 270 = 2 Initial mass = 100mg Final mass = 100 x (1 / 2)n => 100 x (1 / 2)2 =100 x 1 / 4 = 25mg .
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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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