How long does it take for 5.05 g of a radioactive isotope to decay to 0.0505 g if its half-life is 20,000 y?

Question

Quizplus · Accepted Answer

The amount of the isotope decreases by a factor of 100 (from 5.05 g to 0.0505 g), which corresponds to 2^x = 100 (since each half-life halves the amount). Solving for x gives approximately 6.64, meaning it takes about 6.64 half-lives. Multiplying 6.64 by the half-life duration (20,000 years) gives approximately 133,000 years.

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