Question 1

What is a half-life?

Accepted Answer

A half-life (t½) is the time required for half of a radioactive substance to decay. After one half-life, 50% remains; after two half-lives, 25% remains; after three, 12.5%, and so on.

Question 2

Does half-life depend on the amount of substance?

Accepted Answer

No. Half-life is a characteristic property of each radioactive isotope and does not depend on the amount present. Whether you start with 1 gram or 1 kilogram, the same fraction decays in each half-life period.

Question 3

What are some common half-lives?

Accepted Answer

Carbon-14: 5,730 years (used in carbon dating). Uranium-238: 4.5 billion years. Iodine-131: 8 days (medical use). Polonium-214: 164 microseconds. Cobalt-60: 5.27 years (radiation therapy).

Question 4

What is the relationship between half-life and decay constant?

Accepted Answer

The decay constant (λ) = ln(2) / t½ = 0.693 / t½. The decay constant is the probability of decay per unit time and appears in the exponential form: N = N₀ × e^(-λt).

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