Neutron molar mass

$M(n)$ = 1.008 664 917 12(51) × 10⁻³ kg mol⁻¹

Value: 1.008 664 917 12 × 10⁻³ kg mol⁻¹
Standard uncertainty: 5.1 × 10⁻¹³ kg mol⁻¹
Relative uncertainty: 5.1 × 10⁻¹⁰ (506 parts per trillion)
Status: Measured
Symbol: $M(n)$
Source: CODATA 2022 via NIST · NIST entry

Use in a calculation

# neutron molar mass, CODATA 2022 (NIST)
neutron_molar_mass = 1.00866491712e-3  # kg mol^-1, standard uncertainty 5.1e-13

# SciPy: scipy.constants.physical_constants['neutron molar mass']

What it is

The mass of one mole of neutrons (neutron), in kilograms per mole.

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	1.008 664 917 12(51) × 10⁻³	5.1 × 10⁻¹⁰	+2.7 σ of 2018
2018	1.008 664 915 60(57) × 10⁻³	5.7 × 10⁻¹⁰	−0.6 σ of 2014
2014	1.008 664 915 88(49) × 10⁻³	4.9 × 10⁻¹⁰	−0.3 σ of 2010
2010	1.008 664 916 00(43) × 10⁻³	4.3 × 10⁻¹⁰	+0.1 σ of 2006
2006	1.008 664 915 97(43) × 10⁻³	4.3 × 10⁻¹⁰	+0.7 σ of 2002
2002	1.008 664 915 60(55) × 10⁻³	5.5 × 10⁻¹⁰	−0.3 σ of 1998
1998	1.008 664 915 78(55) × 10⁻³	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).