What is the state of the net magnetization vector (NMV) before a sample is introduced to a magnetic field?

Before a sample is introduced to a magnetic field, the net magnetization vector (NMV) is zero due to the random orientation of protons within the sample. In the absence of an external magnetic field, the protons within the material exhibit a random distribution of orientations because their magnetic moments are not aligned. This randomness leads to no net magnetization; essentially, any magnetic moments pointing in one direction are canceled out by those pointing in the opposite direction.

When a magnetic field is applied, the protons begin to align more consistently with the direction of the field, resulting in a net magnetization vector that is not zero. This phenomenon is critical in MRI imaging, as it is the alignment of protons within a strong magnetic field that allows for the creation of meaningful images through RF pulse excitation and subsequent relaxation signals. Thus, the state of the NMV prior to exposure to a magnetic field is characterized by a complete lack of alignment among protons, resulting in a net value of zero.