alpha particle big bang carbon chemical element copper decay chain deuterium equilibrium fractionation half-life hydrogen iron island of stability isotope isotope fractionation isotope geochemistry isotopes of promethium isotopes of technetium kinetic fractionation lead mass-independent fractionation mass spectrometry molybdenum nitrogen nucleosynthesis oxygen promethium radiogenic radiometric dating radionuclide solar system sulfur table of nuclides technetium tin xenon zinc