1. n. [Formation Evaluation]
The loss of coherent energy by protons in a rock while precessing about a static magnetic field during a nuclear magnetic resonance measurement. The loss of coherent energy, or relaxation, due to the free induction decay is corrected by the CPMG pulse sequence. This leaves three mechanisms for relaxation: surface relaxation, bulk relaxation and diffusion relaxation, all of which depend on formation properties. Transverse relaxation is characterized by an exponential decay of time constant T2.