Neutron mass in u
Atomic & nuclearMeasured
= 1.008 664 916 06(40) u
- Value
- 1.008 664 916 06 u
- Standard uncertainty
- 4 × 10−10 u
- Relative uncertainty
- 4.0 × 10−10 (397 parts per trillion)
- Status
- Measured
- Symbol
- Source
- CODATA 2022 via NIST · NIST entry
Use in a calculation
# neutron mass in u, CODATA 2022 (NIST)
neutron_mass_in_u = 1.00866491606 # u, standard uncertainty 4e-10
# SciPy: scipy.constants.physical_constants['neutron mass in u']What it is
The rest mass of the neutron, the electrically neutral nucleon, 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) | 1.674 927 500 57 × 10−24 | |
| MeV/c² MeV / c² | 939.565 421 938 | |
| GeV/c² GeV / c² | 0.939 565 421 938 |
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 | 1.008 664 916 06(40) | 4.0 × 10−10 | +0.2 σ of 2018 |
| 2018 | 1.008 664 915 95(49) | 4.9 × 10−10 | +0.1 σ of 2014 |
| 2014 | 1.008 664 915 88(49) | 4.9 × 10−10 | −0.3 σ of 2010 |
| 2010 | 1.008 664 916 00(43) | 4.3 × 10−10 | +0.1 σ of 2006 |
| 2006 | 1.008 664 915 97(43) | 4.3 × 10−10 | +0.7 σ of 2002 |
| 2002 | 1.008 664 915 60(55) | 5.5 × 10−10 | −0.3 σ of 1998 |
| 1998 | 1.008 664 915 78(55) | 5.5 × 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).