An effect in nuclear magnetic resonance (NMR) used to increase the intensities of resonance lines. The large population differences between the states given by the Boltzmann distribution gives rise to strong intensities of resonance lines. In the nuclear Overhauser effect, spin relaxation is used to transfer population difference from one type of nucleus to another type of nucleus so that the intensities of the resonance lines of the second type of nucleus are increased. An example of such an enhancement, which is widely used, is between protons and 13C, in which case it is possible to attain enhancement of about three times. In the NOE proton, irradiation is used to produce the enhancement of the 13C line. Another use of the NOE is to determine the distance between protons.