Half-life

Definition

Half-life is the time required for half of the radioactive nuclei in a sample to decay. It is a measure of the stability and decay rate of radioactive isotopes.

5 Must Know Facts For Your Next Test

1. The half-life of a substance is constant and does not depend on the initial amount of the substance.
2. Half-life can be used to determine the age of archaeological samples through radiocarbon dating.
3. The formula to calculate remaining quantity after a certain number of half-lives is $N(t) = N_0 \left(\frac{1}{2}\right)^{\frac{t}{T_{1/2}}}$, where $N(t)$ is the remaining quantity, $N_0$ is the initial quantity, $t$ is time elapsed, and $T_{1/2}$ is the half-life.
4. Different isotopes have different half-lives, ranging from fractions of a second to billions of years.
5. Knowledge of half-life helps in medical applications such as cancer treatments using radioisotopes.

Review Questions

• What does it mean when we say an isotope has a half-life of 5 years?
• How would you calculate the remaining amount of a radioactive substance after three half-lives?
• Why is understanding half-life important in fields like archaeology and medicine?

Related terms

Radioactive Decay:

The process by which an unstable atomic nucleus loses energy by emitting radiation.

Activity:

A measure of the number of decays per unit time from a radioactive source; commonly measured in becquerels (Bq).

Isotope:

Variants of elements that have the same number of protons but different numbers of neutrons in their nuclei.