Unstable atoms gain stability by transforming into different nuclides and gradually decaying until the nucleus is balanced, explains the Environmental Protection Agency. This can take a number of different transformations, because the newly produced nuclides are often still unstable. This is a process known as radioactive decay, and takes a different amount of time depending on the type of atom reaching stability.
Atoms are either stable or unstable. Unstable atoms, or radionuclides, have unbalanced forces that cause them to constantly vibrate and contort. This instability results in the atoms constantly emitting energy and engaging in radioactive decay until they reach a level of stability.
Unstable atoms gradually transform over time. Often, they simply transform into another radioactive ion of the same material. Given enough time, however, these atoms transform into nuclides that have a balance of charged subatomic particles in their nucleus. This means they no longer contort, vibrate, decay, or give off large amounts of energy. The amount of time it takes for a quantity of unstable atoms to be decreased to one-half the original level of instability is called its half-life. Different types of radioactive materials have different half-lifes, but the process always involves the same mechanism of radioactive decay.