/ˈaɪsətəʊp ||; ˈaɪsəˌtop/noun [C] (in chemistry 化学) one of two or more forms of a chemical element that have different physical characteristics but the same chemical characteristics 同位素（两个或以上化学特性相同，但物理特性不同的化学元素） Isotopes of the same element have the same number of protons in the nucleus, but a different number of neutrons. 同一元素的同位素(isotope)原子核中含等量的质子(proton)，但不等量的中子(neutron)。