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Radiometric Dating Principles Note 4 - Radiometric dating uses the half-life of unstable isotopes to estimate the age of the rock - method can only be used if rock was in a closed system (no way for addition or loss of parent or daughter isotopes) * Unstable isotopes (like Uranium 238) decay into more stable daughter products by emitting particles * Some isotopes will produce many unstable daughter products before becoming stable Radioactive decay – unstable atom (too many neutrons compared to protons) emits particle to become more stable Steps in Uranium 238 decay to lead 206 Types of Radioactive decay A. Alpha emission– parent emits an alpha particle (2 protons + 2 neutrons) - mass # reduced by 4, - atomic # reduced by 2 B. Beta emission: parent emits an electron - mass # stays same, - atomic # increases by 1 Alpha emission – Note the mass number is decreased by 4 (how has the atomic # changed? Beta emission – note mass # stays the same, how has the atomic # changed? If a radioactive isotope of Uranium (atomic number 92, mass number 238) emits 4 alpha particles and 2 beta particles during the course of radioactive decay, what are the atomic number and mass number of the daughter product? Answer: U 92 - [ 4 (2α ) – 2 ( -1β)] 238 4 0 92 – 8 + 2 = 86(atomic #) (Radon) 238 – 16 222 (mass # )