Lead-207 is a stable isotope of the element lead, which has an atomic number of 82. It is one of the end products of the radioactive decay of uranium and thorium, making it significant in the study of nuclear physics and geochronology. This isotope has a mass number of 207 and does not undergo further radioactive decay, which means it remains unchanged over time. Lead-207 is often used in dating geological samples and understanding the age of rocks and minerals through methods like uranium-lead dating.