Isotopes of helium 氦的同位素
(重定向自Diproton)
Although there are nine known isotopes of helium (He) (relative atomic mass: 4.002602(2)), only helium-3 (3He) and helium-4 (4He) are stable. All radioisotopes are short-lived, the longest-lived being 6He with a half-life of 7002806700000000000♠806.7 milliseconds. The least stable is 5He, with a half-life of 6978760000000000000♠7.6×10 s, although it is possible that 2He has an even shorter half-life.