25 % This table shows that the amount of reactant remaining following n first-order reaction half-lives is (1/2)n times the initial concentration.
As a result, 50% of the original parent nuclei are still present after one half-life, 25% after two half-lives, etc. The half-life and the initial quantity of radioactive atoms present both affect how much radiation is produced by a radioactive source.
Therefore, after two half-lives, the parent-to-daughter atom ratio is 1:3. (one-quarter to three-quarters). The original parent is reduced to an eighth, a sixteenth, a thirty-second, and so on via successive half-lives.
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