A radioactive sample has an initial mass of 80 g and a half-life of 6 hours. Calculate the mass of the original isotope remaining after 18 hours.

Nuclear Physics Challenge #1 — Half-Life

Half-life
of a sample.

Nuclear Physics Easy

Problem

A radioactive isotope has a half-life of 6 hours. A sample starts with a mass of 80 g. Calculate the mass of the original isotope remaining after 18 hours.

Initial mass\( m_0 = 80\ \mathrm{g} \)
Half-life\( t_{1/2} = 6\ \mathrm{h} \)
Time elapsed\( t = 18\ \mathrm{h} \)
Answer ingrams

The decayed atoms don’t vanish — they’ve become a different element.

Hint: how many half-lives fit into 18 hours? Halve the mass once for every one of them.

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Half-lifeof a sample.

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Half-life
of a sample.