lead208

Lead-208 (208Pb) is the stable isotope of lead with 82 protons and 126 neutrons. It is the heaviest known stable nucleus and is doubly magic, as both proton and neutron numbers correspond to closed shells (Z = 82, N = 126). The nucleus is highly bound and nearly spherical, making it a key benchmark for nuclear structure theories.

In nature, lead has four stable isotopes: 204Pb, 206Pb, 207Pb, and 208Pb. Among them, 208Pb is the most abundant, accounting for about 52% of natural lead. It is produced as the stable end product of the thorium-232 decay chain and accumulates in geological materials through the long-term decay of thorium and uranium series.

208Pb holds particular significance in nuclear physics as a paradigm of a doubly magic nucleus. Its structure reflects strong shell effects, minimal deformation, and a characteristic low-lying excitation spectrum, contributing to its role as a testing ground for nuclear models.

Applications and uses: In geochronology, Pb-Pb dating relies on the radiogenic growth of 208Pb to determine ages of rocks and meteorites by comparing isotopic ratios such as 208Pb/206Pb and 208Pb/207Pb. The stability and natural abundance of 208Pb also make lead a common shielding material in radiation protection and a calibration reference in mass spectrometry and detector instrumentation. Its atomic mass is approximately 207.97665 u.