Neutron Compton wavelength

$λ_C,n$ = 1.319 590 903 82(67) × 10⁻¹⁵ m

Value: 1.319 590 903 82 × 10⁻¹⁵ m
Standard uncertainty: 6.7 × 10⁻²⁵ m
Relative uncertainty: 5.1 × 10⁻¹⁰ (508 parts per trillion)
Status: Measured
Symbol: $λ_C,n$
Source: CODATA 2022 via NIST · NIST entry

Use in a calculation

# neutron Compton wavelength, CODATA 2022 (NIST)
neutron_compton_wavelength = 1.31959090382e-15  # m, standard uncertainty 6.7e-25

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

What it is

The wavelength of a photon whose energy equals the rest energy of the neutron, the electrically neutral nucleon: h/(mc).

In other units

Unit	Value
CGS (cm)	1.319 590 903 82 × 10⁻¹³
pm picometre	0.001 319 590 903 82
fm femtometre	1.319 590 903 82

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	1.319 590 903 82(67) × 10⁻¹⁵	5.1 × 10⁻¹⁰	−2.7 σ of 2018
2018	1.319 590 905 81(75) × 10⁻¹⁵	5.7 × 10⁻¹⁰	+1.1 σ of 2014
2014	1.319 590 904 81(88) × 10⁻¹⁵	6.7 × 10⁻¹⁰	−1.8 σ of 2010
2010	1.319 590 9068(11) × 10⁻¹⁵	8.3 × 10⁻¹⁰	+5.8 σ of 2006
2006	1.319 590 8951(20) × 10⁻¹⁵	1.5 × 10⁻⁹	−1.3 σ of 2002
2002	1.319 590 9067(88) × 10⁻¹⁵	6.7 × 10⁻⁹	+0.9 σ of 1998
1998	1.319 590 898(10) × 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).