In [[radioactivity]] logging for uranium. After a long period of disintegration, if the radioactive parent and its daughter [[isotopes]] remain undisturbed, equilibrium will be attained between the production and [[decay]] of the respective radioactive materials. Since U-238 does not emit [[gamma ray|gamma rays]], the gamma-ray activity recorded is due to the quantity of daughter isotopes. When U-238 is in equilibrium with its daughter isotopes, the amount of daughter isotopes detected is an index to the amount of U-238 present. Disequilibrium results when anything has occurred to disturb the relative quantities of radioactive materials (selective leaching, escape of radon gas, etc.).