A neutrophile is a substance which is attracted to the neutrons in the nucleus of an atom, on account of its own lack of neutrons. Due to this attraction, a reaction usually takes place within the two substances. Neutrophiles are used to find the rates of formation of isotopes, and thus the rate of decay of radioactive substances. Because isotopes (produced from radioactive decay) are the same substance except with differing numbers of neutrons, the tendency of neutrophiles to react with each isotope varies. Because it is known what is produced when a neutrohile and a certain isotope react together, by measuring the rate of production of these substances scientists can work out the overall rate of production of the isotope itself (and thus the rate of decay).