A type of nucleus in which it is statistically unlikely that there will be more than one such nucleus in a molecule (unless the substance has been artificially enriched with isotopes having that nucleus). An example of a dilute spin species is ¹³C since it has a natural abundance of 1.1%. This means that for dilute spin systems it is usually not necessary to consider spin-spin interactions between two nuclei of the dilute spin species, e.g. ¹³C–¹³C in the same molecule. The opposite of a dilute spin species is an abundant spin species, an example being the proton.