Final answer:
The accumulation of aligned low thermal energy protons in an external static magnetic field is termed magnetization, which is a key aspect of Nuclear Magnetic Resonance (NMR).
Step-by-step explanation:
The accumulation of low thermal energy protons that align with an external static magnetic field is known as magnetization. This phenomenon is observed in Nuclear Magnetic Resonance (NMR) where the magnetic dipoles, or spins, align with the external field due to interactions that cause them to be in either a low or high energy state. The potential energy associated with the magnetic interaction is described by the equation U = −μ · B, where μ represents the magnetic moment and B the external magnetic field. Depending on their alignment (parallel or antiparallel) with the field, the energy states of the spins will differ. When energy in the form of radio frequency is applied, transitions between these states can occur, leading to the absorption and re-emission of this energy, a fundamental principle of NMR.