The half-life of protactinium-231 is 3.25 × 10⁴ years. How long will it take for 10.4 grams of Pa-231 to decay to 2.6 grams?

Name: The half-life of protactinium-231 is 3.25 × 10 4 years. How long will it take for 10.4 grams of Pa-231 to decay to 2.6 grams?
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Quizplus · Accepted Answer

The decay from 10.4 grams to 2.6 grams means the substance has gone through two half-lives (10.4 to 5.2 to 2.6). Since the half-life of Pa-231 is 3.25 × 10^4 years, two half-lives would take 2 × 3.25 × 10^4 = 6.5 × 10^4 years.

The Half-Life of Protactinium-231 Is 3