What is Nuclear magnetic resonance?
'''Nuclear magnetic resonance''' (NMR) is the [[Physical law|physical]] phenomenon in which [[magnetic nuclei]] in a [[magnetic field]] absorb, then re-emit [[electromagnetic radiation]]. This [[energy]] is of a specific [[resonance]] [[frequency]] that depends on the magnetic [[field strength]], and the [[Magnet|magnetic]] properties of the [[isotope]]s of the atoms. Many scientific [[Technique|techniques]] use it to study [[molecular physics]], [[crystal]]s and non crystalline materials through NMR [[spectroscopy]]. NMR is also used for advanced [[medical]] imaging techniques, for example, [[magnetic resonance imaging]] (MRI). ==How it works== All [[Isotope|isotopes]] that contain an odd number of [[proton]]s and/or of [[neutrons]] (see [[Isotope#Even and odd|Isotope]]) have an intrinsic [[Magnetic moment#Magnetic moment of a nucleus|magnetic moment]] and [[angular momentum]], in other words a nonzero [[Spin (physics)|spin]], while all [[nuclide]]s with even numbers of both have a total spin of zero. The most commonly studied nuclei are <sup>1</sup>H and <sup>13</sup>C, although nuclei from isotopes of many other elements (e.g. <sup>2</sup>H, <sup>6</sup>Li, <sup>10</sup>B, <sup>11</sup>B, <sup>14</sup>N, <sup>15</sup>N, <sup>17</sup>O, <sup>19</sup>F, <sup>23</sup>Na, <sup>29</sup>Si, <sup>31</sup>P, <sup>35</sup>Cl, <sup>113</sup>Cd, <sup>129</sup>Xe, <sup>195</sup>Pt) have been studied by high-field NMR spectroscopy as well. A key idea of NMR is that the [[resonance]] frequency of a particular substance is directly proportional to the strength of the applied magnetic field. This resonance is used in imaging techniques. If a sample is placed in a non-uniform magnetic field then the resonance frequencies of the sample's nuclei depend on where in the field they are located. Scientists try to use the highest possible magnetic fields to get the best image quality. The principle of NMR usually involves two [[Sequence|sequential]] steps: *The alignment ([[polarization]]) of the magnetic nuclear spins in an appl