Answer :
After 39.1 years, which is just over three half-lives of tritium (hydrogen-3) with a half-life of 12.3 years, slightly more than 12.5% of an original tritium sample would remain.
The half-life of a radioactive isotope, such as hydrogen-3 (also known as tritium), is the time it takes for half of a given sample to decay into another element.
In this case, tritium decays into helium-3 by emitting a beta particle.
If the half-life of tritium is 12.3 years, after one half-life (12.3 years), 50% of the original sample would remain.
After two half-lives (24.6 years), only 25% would be left.
After three half-lives (36.9 years), the amount remaining would be halved again, resulting in 12.5% of the original sample.
Given that 39.1 years is just over three half-lives for tritium, the percentage of the sample left will be slightly more than 12.5%, as it hasn't quite reached the fourth half-life mark.
Therefore, after 39.1 years, the percentage of a sample of tritium left would be slightly above 12.5%.
