Radioactivity

Becquerel accidentally found that a uranium-rich mineral emitted invisible, penetrating rays that could darken a photographic plate.

Radioactive decay occurs when an unstable atomic nucleus emits particles or light waves.

Radioactive decay rate is exponential and is characterized by constants, such as half-life, as well the activity and number of particles.

The half-life is a parameter for the rate of decay that is related to the decay constant by: ${t}_{\frac{1}{2}}=\frac{ln2}{\lambda}$ .

Radiometric dating is used to date materials using the decay rate of a radioactive isotope.