Some elements have several isotopes while others may have only one isotope.
Such ejection process is called the radioactive decay.Isotope - Atoms with the same number of protons but different number of neutrons are called isotopes.By changing the number of neutrons, isotopes still maintain the same overall neutrality and hence the chemical behavior remains unchange.(An exception is the common form of hydrogen, whose nucleus consists of a lone proton.) Every chemical element has more than one isotope.For any element, one of the isotopes is more abundant in nature than any of the others, although often multiple isotopes of a single element are mixed.
Archaeologists use the exponential, radioactive decay of carbon 14 to estimate the death dates of organic material.