Positively and spin motion of the nucleus, and its spin motion will have a magnetic moment, known as the nuclear magnetic moment. Studies have shown that nuclear magnetic moment μ and the nucleus is proportional to the spin angular momentum s, γ in k is called the gyromagnetic ratio of the nucleus. In the external magnetic field, and spatial orientation of the nuclear spin angular momentum is quantized, it projected values in the direction of the magnetic field can be expressed as m for nuclear spin quantum number.
Based on the relationship between nuclear magnetic moment and spin angular momentum, nuclear magnetic moment in a magnetic field orientations are quantized, projection on it when the field value is for a different kernel, m takes integer or half-integer, respectively. In the external magnetic field, has a magnetic moment of the nucleus has a corresponding energy, its value can be expressed as a type b is the magnetic induction. Nuclear energy in outer magnetic field is quantized. Due to the interaction between the magnetic moment and the magnetic field, spin-energy split into a series of discrete energy levels, difference between adjacent two-level δ e = γ hB. Appropriate exposure to electromagnetic radiation of the atomic nucleus by frequency, electromagnetic radiation photon energy h ν if exactly two adjacent levels of nuclear energy difference ΔE, the nucleus will absorb the photon, NMR frequencies are:-ν is the frequency, ω is the angular frequency. For nuclear, gyromagnetic ratio γ can be accurately measured. Obviously, by measuring the radiation when the frequency ν of nuclear magnetic resonance, magnetic flux density will be ascertained; Conversely, if known magnetic flux density, nuclear resonance frequency can be determined.
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