In NMR spectroscopy, receptivity refers to the relative detectability of a particular element. Some elements are easily detected, some less so. The receptivity is a function of the abundance of the element's NMR-responsive isotope and that isotope's gyromagnetic ratio (or equivalently, the nuclear magnetic moment). Some isotopes, tritium for example, have large gyromagnetic ratios but low abundance. Other isotopes, for example <sup>103</sup>Rh, are highly abundant but have low gyromagnetic ratios. Widely used NMR spectroscopies often focus on highly receptive elements: <sup>1</sup>H, <sup>19</sup>F, and <sup>31</sup>P.