Isotopic abundance

Isotopic abundance (or abundance of isotopes ) is the relative number of atoms of different isotopes of one chemical element ; it is usually expressed as% of the sum of the atoms of all long-lived (with a half-life T> 3⋅10 ⁸ years) of isotopes of this element on average in nature (or with reference to a particular environment, planet, region, etc.). An accurate measurement of the isotopic abundance is of great importance for determining the atomic masses of elements.