Alpha particle mass in u
Atomic & nuclearMeasured
= 4.001 506 179 129(62) u
- Value
- 4.001 506 179 129 u
- Standard uncertainty
- 6.2 × 10−11 u
- Relative uncertainty
- 1.5 × 10−11 (15 parts per trillion)
- Status
- Measured
- Symbol
- Source
- CODATA 2022 via NIST · NIST entry
Use in a calculation
# alpha particle mass in u, CODATA 2022 (NIST)
alpha_particle_mass_in_u = 4.001506179129 # u, standard uncertainty 6.2e-11
# SciPy: scipy.constants.physical_constants['alpha particle mass in u']What it is
The rest mass of the alpha particle, the nucleus of helium-4 (two protons and two neutrons), in unified atomic mass units (daltons), where 1 u is one twelfth of the mass of a carbon-12 atom.
In other units
| Unit | Value | |
|---|---|---|
| CGS (g) | 6.644 657 344 97 × 10−24 | |
| MeV/c² MeV / c² | 3727.379 411 85 | |
| GeV/c² GeV / c² | 3.727 379 411 85 |
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 | 4.001 506 179 129(62) | 1.5 × 10−11 | +0.0 σ of 2018 |
| 2018 | 4.001 506 179 127(63) | 1.6 × 10−11 | +0.0 σ of 2014 |
| 2014 | 4.001 506 179 127(63) | 1.6 × 10−11 | +0.0 σ of 2010 |
| 2010 | 4.001 506 179 125(62) | 1.5 × 10−11 | −0.0 σ of 2006 |
| 2006 | 4.001 506 179 127(62) | 1.5 × 10−11 | −0.4 σ of 2002 |
| 2002 | 4.001 506 179 149(56) | 1.4 × 10−11 | +4.4 σ of 1998 |
| 1998 | 4.001 506 1747(10) | 2.5 × 10−10 |
“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).