Alpha particle mass
Atomic & nuclearMeasured
= 6.644 657 3450(21) × 10−27 kg
- Value
- 6.644 657 3450 × 10−27 kg
- Standard uncertainty
- 2.1 × 10−36 kg
- Relative uncertainty
- 3.2 × 10−10 (316 parts per trillion)
- Status
- Measured
- Symbol
- Source
- CODATA 2022 via NIST · NIST entry
Use in a calculation
# alpha particle mass, CODATA 2022 (NIST)
alpha_particle_mass = 6.644657345e-27 # kg, standard uncertainty 2.1e-36
# SciPy: scipy.constants.physical_constants['alpha particle mass']What it is
The rest mass of the alpha particle, the nucleus of helium-4 (two protons and two neutrons), in kilograms.
In other units
| Unit | Value | |
|---|---|---|
| CGS (g) | 6.644 657 345 × 10−24 | |
| u dalton / atomic mass unit | 4.001 506 179 | unit is itself measured |
| MeV/c² MeV / c² | 3727.379 4119 | |
| GeV/c² GeV / c² | 3.727 379 4119 |
Converted with ConstantID's unit table; digits are rounded to the precision of the value, and a long exact value is rounded only for display. The relative uncertainty is unchanged by conversion to an exactly defined unit.
How the value changed, 1998–2022
Each point is one CODATA adjustment, plotted as its difference from the 2022 value; the bars show one standard uncertainty (an arrowhead means the bar runs off the chart).
Relative uncertainty
| CODATA | Value (uncertainty) | Relative uncertainty | Change from previous |
|---|---|---|---|
| 2022 | 6.644 657 3450(21) × 10−27 | 3.2 × 10−10 | +4.7 σ of 2018 |
| 2018 | 6.644 657 3357(20) × 10−27 | 3.0 × 10−10 | +1.3 σ of 2014 |
| 2014 | 6.644 657 230(82) × 10−27 | 1.2 × 10−8 | +1.7 σ of 2010 |
| 2010 | 6.644 656 75(29) × 10−27 | 4.4 × 10−8 | +1.7 σ of 2006 |
| 2006 | 6.644 656 20(33) × 10−27 | 5.0 × 10−8 | −0.3 σ of 2002 |
| 2002 | 6.644 6565(11) × 10−27 | 1.7 × 10−7 | +1.0 σ of 1998 |
| 1998 | 6.644 655 98(52) × 10−27 | 7.8 × 10−8 |
“Change from previous” is the shift in the value divided by the standard uncertainty of the previous adjustment. Earlier values are converted into the current unit where NIST changed it (for example J s to J Hz⁻¹).