He
Helium
Z = 2 · Noble Gas · 4.003 u
Nuclear Engineering Significance
Coolant in high-temperature gas-cooled reactors (HTGRs) due to chemical inertness and low neutron absorption. He-3 has an enormous thermal absorption cross-section (σ_a = 5,330 b) and is used in neutron detectors. He-4 is produced by alpha decay of actinides in spent fuel.
Basic properties
- Atomic number (Z)
- 2
- Standard atomic mass
- 4.003 u
- Category
- Noble Gas
Isotopes & cross-section data
| Isotope | Mass (A) | Half-life | ZAID | Libraries |
|---|---|---|---|---|
| He-3 | 3 | Stable | .80c.71c.70c | |
| He-4 | 4 | Stable | .80c.71c.70c |