镎的同位素

备注：画上#号的数据代表没有经过实验的证明，只是理论推测而已，而用括号括起来的代表数据不确定性。

Neptunium (Np) is an artificial element, and thus a standard atomic mass cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was Np in 1940, produced by bombarding U with neutrons to produce U, which then underwent beta decay to Np.