Nuclear decay is a natural process where unstable atomic nuclei lose energy by emitting radiation. This can happen in several ways, such as through alpha decay, where an atom releases an alpha particle, or beta decay, where a neutron transforms into a proton and emits a beta particle. Over time, this process changes the original element into a different one, often leading to a stable form. As a result of nuclear decay, the original element's quantity decreases, while the new element's quantity increases. This transformation is measured using the concept of half-life, which is the time it takes for half of the original substance to decay.