Physical principle An atomic nucleus having an uneven number of protons and/or neutrons, as hydrogen (1H) or fluorine (19F), carries a nuclear magnetic dipole moment, resulting from its spin-angular momentum, comparable to a small magnetic compass needle. Without a mag-netic field, the dipole moments within a specimen are randomly orientated (Figure 1a). If the specimen is placed into a static magnetic field B0 the magnetic moments are orien-tated anti-parallel or parallel to the B0 direction (Figure 1b). The latter is the low-energy state, leading to a slightly overbalanced population of the in-field orientation in thermal equilibrium. This excess population provides a detectable macroscopic magnetization in the specimen. In a more classical explanation of the Nuclear Magnetic Resonance (NMR) phenome-non, each dipole moment precesses around an axis parallel to B0 with a characteristic angular frequency, called the Larmor frequency omega0. It depends on the on the type of the observed nuclear species (gyromagnetic ratio gamma) and it is directly proportional to the strength of the magnetic field.
|Title of host publication||Advanced Testing of Cement-Based Materials during Setting and Hardening - Final Report of RILEM TC 185-ATC|
|Editors||H.W. Reinhardt, C.U. Grosse|
|Number of pages||21|
|Publication status||Published - 2006|