Age determination by means of radionuclides

The present report describes various aspects of age determination using radioactive isotopes, focusing on radioactive decay, events in the past, history from the formation of elements until the formation of the Earth, age of the Earth, time of solidification of rock, age determination by means of radioactive carbon 14C, and age determination from non-equilibrium among uranium-related radioactive nuclides. Long-lived radioactive nuclides such as 40K and 87Rb are widely used for estimating the time of solidification of rock. While an anthropologist may use 40K in determining the age of objects older than 1,000,000 years to trace the history of the human evolution, an archaeologist will rely on 14C for determination of an age less than 100,000 years. In the case of uranium series, a non-equilibrium takes place between parents and daughters contained in an object. This non-equilibrium state is attributable to the alpha recoil. Thus, the 234U/238U ratio in underground water increases with the retention time of the water in the ground. The ratio, therefore, provides a tool for age determination of underground water. (N.K.)