relative proportion of an isotope as found in nature; abundance of isotopes of a chemical element as naturally found on a planet
Relative abundance of elements in the Earth's upper crust In physics, natural abundance (NA) refers to the abundance of isotopes of a chemical element as naturally found on a planet. The relative atomic mass (a weighted average, weighted by mole-fraction abundance figures) of these isotopes is the atomic weight listed for the element in the periodic table. The abundance of an isotope varies from planet to planet, and even from place to place on the Earth, but remains relatively constant in time (on a short-term scale).
As an example, uranium has three naturally occurring isotopes: U, U, and U. Their respective natural mole-fraction abundances are 99.2739–99.2752%, 0.7198–0.7202%, and 0.0050–0.0059%. For example, if 100,000 uranium atoms were analyzed, one would expect to find approximately 99,274 U atoms, approximately 720 U atoms, and very few (most likely 5 or 6) U atoms. This is because U is much more stable than U or U, as the half-life of each isotope reveals: 4.468 billion years for U compared with 7.038 × 10 years for U and 245,500 years for U.
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).