With no explanation, label text_A→text_B with either "not_related" or "related".
text_A: Richard Nixon's wife was born in March.
text_B: Spin diffusion describes a situation wherein the individual nuclear spins undergo continuous exchange of energy .. spins. spin ( physics ). This permits polarization differences within the sample to be reduced on a timescale much shorter than relaxation effects .. polarization. Spin polarization. relaxation. relaxation time. Spin diffusion is a process by which magnetization can be exchanged spontaneously between spins .. spins. spin ( physics ). The process is driven by dipolar coupling , and is therefore related to internuclear distances .. Spin diffusion has been used to study many structural problems in the past , ranging from domain sizes in polymers and disorder in glassy materials to high-resolution crystal structure determination of small molecules and proteins .
not_related.