Neutron-proton magnetic moment ratio

$μₙ/μₚ$ = −0.684 979 35(16)

Value: −0.684 979 35
Standard uncertainty: 1.6 × 10⁻⁷
Relative uncertainty: 2.3 × 10⁻⁷ (234 parts per billion)
Status: Measured
Symbol: $μₙ/μₚ$
Source: CODATA 2022 via NIST · NIST entry

Use in a calculation

# neutron-proton magnetic moment ratio, CODATA 2022 (NIST)
neutron_proton_magnetic_moment_ratio = -6.8497935e-1  # standard uncertainty 1.6e-7

# SciPy: scipy.constants.physical_constants['neutron-proton mag. mom. ratio']

What it is

The magnetic moment of the neutron divided by the magnetic moment of the proton. Ratios like this are often measured more precisely than either quantity on its own, which is why CODATA lists them.

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	−0.684 979 35(16)	2.3 × 10⁻⁷	−0.1 σ of 2018
2018	−0.684 979 34(16)	2.3 × 10⁻⁷	+0.0 σ of 2014
2014	−0.684 979 34(16)	2.3 × 10⁻⁷	+0.0 σ of 2010
2010	−0.684 979 34(16)	2.3 × 10⁻⁷	+0.0 σ of 2006
2006	−0.684 979 34(16)	2.3 × 10⁻⁷	+0.0 σ of 2002
2002	−0.684 979 34(16)	2.3 × 10⁻⁷	+0.0 σ of 1998
1998	−0.684 979 34(16)	2.3 × 10⁻⁷

“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).