Final answer:
The half-life of a sample that decreases from 120 units to 60 units in 35 minutes is 35 minutes, as this is the time taken for the activity to reduce by half. The correct answer is A.
Step-by-step explanation:
Understanding Half-Life in Radioactive Decay
The concept of half-life is fundamental in the study of radioactive decay. It is defined as the time required for half of the radioactive nuclei in a sample to undergo decay, resulting in a reduction by half of its initial activity. The question presents a scenario in which an initial activity of 120 units drops to 60 units in 35 minutes. Here, we can conclude that the half-life of the sample is 35 minutes, which corresponds to Option A. This is because the half-life is the period in which a sample's activity is reduced by 50%, which exactly matches the scenario described.
To elaborate with an example, if a substance has a half-life of 35 minutes, after 35 minutes, only half of the original quantity of the substance would remain unchanged or undecayed. This exponential decay process is a characteristic of radioactive materials, and understanding it is key to various applications including medical imaging, carbon dating, and nuclear power generation.
When we apply the concept of half-life to the provided references, for instance, a 3 half-life period would leave N/8 of the original atoms, since each half-life reduces the sample by half: N (initial) → N/2 (after 1 half-life) → N/4 (after 2 half-lives) → N/8 (after 3 half-lives).