Pr141
Pr141, also written as Pr-141, designates the stable isotope of the element praseodymium with mass number 141. Praseodymium (chemical symbol Pr) has atomic number 59, so Pr-141 contains 59 protons and 82 neutrons. It is the only stable, naturally occurring isotope of praseodymium, and as a result the atomic weight of natural praseodymium is essentially the mass of Pr-141, about 140.90766 atomic mass units.
Natural occurrence and stability: Pr-141 occurs in trace amounts within minerals that contain rare earth elements,
Applications and relevance: In analytical chemistry and geochemistry, Pr-141 serves as a reference isotope for calibration
See also: Praseodymium, isotopes, isotopic abundance, rare earth elements.