Reduced neutron Compton wavelength

$λ̄_C,n$ = 2.100 194 1520(11) × 10⁻¹⁶ m

Value: 2.100 194 1520 × 10⁻¹⁶ m
Standard uncertainty: 1.1 × 10⁻²⁵ m
Relative uncertainty: 5.2 × 10⁻¹⁰ (524 parts per trillion)
Status: Measured
Symbol: $λ̄_C,n$
Source: CODATA 2022 via NIST · NIST entry

Use in a calculation

# reduced neutron Compton wavelength, CODATA 2022 (NIST)
reduced_neutron_compton_wavelength = 2.100194152e-16  # m, standard uncertainty 1.1e-25

# SciPy: scipy.constants.physical_constants['reduced neutron Compton wavelength']

What it is

The Compton wavelength of the neutron, the electrically neutral nucleon, divided by 2π: ħ/(mc).

In other units

Unit	Value
CGS (cm)	2.100 194 152 × 10⁻¹⁴
fm femtometre	0.210 019 4152

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	2.100 194 1520(11) × 10⁻¹⁶	5.2 × 10⁻¹⁰	−2.7 σ of 2018
2018	2.100 194 1552(12) × 10⁻¹⁶	5.7 × 10⁻¹⁰	+1.1 σ of 2014
2014	0.210 019 415 36(14) × 10⁻¹⁵	6.7 × 10⁻¹⁰	−1.9 σ of 2010
2010	0.210 019 415 68(17) × 10⁻¹⁵	8.1 × 10⁻¹⁰	+6.0 σ of 2006
2006	0.210 019 413 82(31) × 10⁻¹⁵	1.5 × 10⁻⁹	−1.3 σ of 2002
2002	0.210 019 4157(14) × 10⁻¹⁵	6.7 × 10⁻⁹	+0.9 σ of 1998
1998	0.210 019 4142(16) × 10⁻¹⁵	7.6 × 10⁻⁹

“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).