Question

The half-life of tritium, or hydrogen-3, is 12.32 years. After about 24.6 years, how much of a sample of tritium will remain unchanged?

Answer 1

The half-life is 12.32 years
24.6 years is approximately double the half-life.

So in 24.6 years, Tritium will pass through 2 half-lives.

If we start with a sample of pure Tritium (denoted by 1 for 100% Tritium):

1 * 0.5 = 0.5 Tritium after 12.32 years
0.5 * 0.5 = 0.25 Tritium after 24.6 years

So 1/4 will be unchanged and still be Tritium.