Alpha particle mass = 6.644 657 3450 × 10−27 kg
- Value
- 6.644 657 3450 × 10−27
- Unit
- kg
- Uncertainty
- 0.000 000 0021 × 10⁻²⁷
- Copy-ready
6.6446573450e-27
Rest mass of the alpha particle — a helium-4 nucleus (two protons, two neutrons), the particle emitted in alpha decay.
Used to compute reaction energies, decay kinematics and binding energies. The lines below give the same mass in kilograms, atomic mass units (u), as an energy (mc², in J and MeV) and per mole, plus its ratio to other particles — all from the same CODATA adjustment, so they agree with each other.
The same quantity, other ways NIST lists it
| Quantity (NIST name) | Value | Unit | Uncertainty |
|---|---|---|---|
| Alpha particle-electron mass ratio | 7294.299 541 71 | (dimensionless) | 0.000 000 17 |
| Alpha particle mass energy equivalent | 5.971 920 1997 × 10−10 | J | 0.000 000 0019 × 10⁻¹⁰ |
| Alpha particle mass energy equivalent in MeV | 3727.379 4118 | MeV | 0.000 0012 |
| Alpha particle mass in u | 4.001 506 179 129 | u | 0.000 000 000 062 |
| Alpha particle molar mass | 4.001 506 1833 × 10−3 | kg·mol⁻¹ | 0.000 000 0012 × 10⁻³ |
| Alpha particle-proton mass ratio | 3.972 599 690 252 | (dimensionless) | 0.000 000 000 070 |
| Alpha particle relative atomic mass | 4.001 506 179 129 | (dimensionless) | 0.000 000 000 062 |
NIST, Fundamental Physical Constants — Complete Listing (2022 CODATA adjustment), retrieved 2026-07-26.