Neutron magnetic moment

$μ_{n}$ = −9.662 3653(23) × 10⁻²⁷ J T⁻¹

Value: −9.662 3653 × 10⁻²⁷ J T⁻¹
Standard uncertainty: 2.3 × 10⁻³³ J T⁻¹
Relative uncertainty: 2.4 × 10⁻⁷ (238 parts per billion)
Status: Measured
Symbol: $μ_{n}$
Source: CODATA 2022 via NIST · NIST entry

Use in a calculation

# neutron magnetic moment, CODATA 2022 (NIST)
neutron_magnetic_moment = -9.6623653e-27  # J T^-1, standard uncertainty 2.3e-33

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

What it is

The magnetic moment of the neutron, the electrically neutral nucleon: how strongly it behaves like a tiny bar magnet. A negative value means it points opposite to the spin.

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	−9.662 3653(23) × 10⁻²⁷	2.4 × 10⁻⁷	−0.1 σ of 2018
2018	−9.662 3651(23) × 10⁻²⁷	2.4 × 10⁻⁷	−0.0 σ of 2014
2014	−0.966 236 50(23) × 10⁻²⁶	2.4 × 10⁻⁷	−0.1 σ of 2010
2010	−0.966 236 47(23) × 10⁻²⁶	2.4 × 10⁻⁷	−0.3 σ of 2006
2006	−0.966 236 41(23) × 10⁻²⁶	2.4 × 10⁻⁷	+0.2 σ of 2002
2002	−0.966 236 45(24) × 10⁻²⁶	2.5 × 10⁻⁷	−0.2 σ of 1998
1998	−0.966 236 40(23) × 10⁻²⁶	2.4 × 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).