U is for Uranium
Uranium is known best for its radioactive isotopes. As scientists working with stable isotopes – and light ones at that – we regularly grapple with the misconception that anything called an “isotope” is radioactive and is a potential component of dirty bombs.
Uranium has many isotopes, all of which are radioactive, which means they are unstable and will spontaneously break down into other stable (not-radioactive) isotopes. The atomic number of uranium is 92, meaning that there are 92 protons int he nucleus. Most uranium in nature is urnaium-238 (92 protons + 146 neutrons), but there is also uranium-235 and uranium-234. Both uranium-238 and uranium-235 decay to form stable isotopes of lead (lead-206 and lead-207, respectively). By measuring the ratios of uranium to lead in these two systems, it is possible to determine ages of rocks that are millions to billions of years old.