He
Helium
Z 2 4.003 g/molNoble Gas
| 4He | 2 | 4.0026 | 2,424.916 | 99.9998% | Stable | 0+ | --- | 1908 |
| 3He | 1 | 3.016 | 14,931.219 | 0.0002% | Stable | 1/2+ | --- | 1934 |
| 5He | 3 | 5.0121 | 11,231.0 | --- | 602.0 ys | 3/2- | n→4He(100%) | 1937 |
| 6He | 4 | 6.0189 | 17,592.1 | --- | 806.92 ms | 0+ | β⁻→6Li(~100%) β⁻→4He(2.78e-4%) | 1936 |
| 7He | 5 | 7.028 | 26,073.0 | --- | 2.51 zs | (3/2-) | n→6He(100%) | 1967 |
| 8He | 6 | 8.0339 | 31,609.68 | --- | 119.5 ms | 0+ | β⁻→8Li(83.1%) β⁻n→7Li(16%) β⁻→5He(0.9%) | 1965 |
| 9He | 7 | 9.044 | 40,940.0 | --- | 2.5 zs | (1/2+) | n→8He(100%) | 1987 |
| 10He | 8 | 10.0528 | 49,200.0 | --- | 260.0 ys | 0+ | n→8He(100%) | 1994 |