Why can a hydrogen nucleus have parallel and antiparallel spin orientations in a magnetic field?

A hydrogen nucleus possesses an intrinsic spin, which gives it a magnetic moment, causing it to behave like a tiny bar magnet. When placed in an external magnetic field, the laws of quantum mechanics dictate that the nucleus can only occupy a limited set of discrete energy states.12

Specifically, the nuclear magnetic moment can orient itself in one of two possible directions relative to the external field: parallel (lower energy) or antiparallel (higher energy). The antiparallel orientation is considered an upper spin state because it requires more energy to align against the external magnetic field. This quantization of energy states is a fundamental aspect of nuclear magnetic resonance (NMR), where these transitions between parallel and antiparallel states are studied by applying electromagnetic radiation of specific frequencies.132