What happens to radioactive isotopes over time?

• A. They become more unstable over time
• B. They instantly disappear
• C. They decay with their half-lives
• D. They never change

Answer: (C)

Radioactive isotopes diminish over time in a predictable, exponential way, determined by their half-life. The half-life is the amount of time it takes for half of a given sample to decay into other elements. So, after one half-life, half remains; after two half-lives, a quarter remains; and so on. This means the population of radioactive nuclei declines steadily, not instantly disappearing and not becoming more unstable over time. In fact, as unstable nuclei decay, they typically move toward more stable configurations, though the decay products can themselves be radioactive. In mathematical terms, the remaining amount is N = N0 × (1/2)^(t/T1/2). This persistence governed by half-lives is why radioactive substances vary in how long they stay hazardous or detectable in the environment.