lead207

Lead-207 (207Pb) is a stable isotope of the element lead (Pb) with 82 protons and a mass number of 207. It is one of the four stable isotopes of lead, alongside 204Pb, 206Pb, and 208Pb, and accounts for roughly 22% of natural lead.

It is the end product of the uranium-235 decay chain (the actinium series). Uranium-235 decays through a series of alpha and beta decays over hundreds of millions of years, ultimately forming stable 207Pb.

Because 207Pb is stable, it has no radioactive decay and a long terrestrial lifetime. It has 82 protons and 125 neutrons. Its natural abundance is used in geochemistry and geochronology.

In geology, the 207Pb/235U and 206Pb/238U decay systems are used for U–Pb dating, often with zircon crystals; the ratios allow ages to be determined and checked via concordia diagrams.

Natural lead isotopic composition is approximately 204Pb (about 1.4%), 206Pb (about 24%), 207Pb (about 22%), and 208Pb (about 52%), though values vary slightly. 207Pb is widely measured by mass spectrometry in isotope geochemistry and is used as a tracer for geological processes and cosmochemistry.