ConstantID

Neutron-electron mass ratio

Atomic & nuclearMeasured

mn/me = 1838.683 662 00(74)

Value
1838.683 662 00
Standard uncertainty
7.4 × 10−7
Relative uncertainty
4.0 × 10−10 (402 parts per trillion)
Status
Measured
Symbol
mn/me
Source
CODATA 2022 via NIST · NIST entry

Use in a calculation

# neutron-electron mass ratio, CODATA 2022 (NIST)
neutron_electron_mass_ratio = 1.838683662e3  # standard uncertainty 7.4e-7

# SciPy: scipy.constants.physical_constants['neutron-electron mass ratio']

What it is

The mass of the neutron divided by the mass of the electron. 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).

neutron-electron mass ratio: CODATA values 1998–2022 relative to the 2022 value, in parts per billion, with one-standard-uncertainty bars−6−4−20+2+4+6parts per billion1998200220062010201420182022

Relative uncertainty

neutron-electron mass ratio: relative standard uncertainty in each CODATA adjustment, logarithmic scale10⁻¹⁰10⁻⁹10⁻⁸1998200220062010201420182022
CODATAValue (uncertainty)Relative uncertaintyChange from previous
20221838.683 662 00(74)4.0 × 10−10 +0.3 σ of 2018
20181838.683 661 73(89)4.8 × 10−10 +0.2 σ of 2014
20141838.683 661 58(90)4.9 × 10−10 +1.0 σ of 2010
20101838.683 6605(11)6.0 × 10−10 +0.0 σ of 2006
20061838.683 6605(11)6.0 × 10−10 +0.5 σ of 2002
20021838.683 6598(13)7.1 × 10−10 +1.2 σ of 1998
19981838.683 6550(40)2.2 × 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).

Related constants

Atomic & nuclear λC,n Neutron Compton wavelength 1.319 590 903 82(67) × 10−15 m Atomic & nuclear μn/μe Neutron-electron magnetic moment ratio 1.040 668 84(24) × 10−3 Atomic & nuclear gn Neutron g factor −3.826 085 52(90) Atomic & nuclear γn Neutron gyromagnetic ratio 1.832 471 74(43) × 108 s−1 T−1 Atomic & nuclear γn/2π Neutron gyromagnetic ratio in MHz/T 29.164 6935(69) MHz T−1 Atomic & nuclear μn Neutron magnetic moment −9.662 3653(23) × 10−27 J T−1 Atomic & nuclear μn/μB Neutron magnetic moment to Bohr magneton ratio −1.041 875 65(25) × 10−3 Atomic & nuclear μn/μN Neutron magnetic moment to nuclear magneton ratio −1.913 042 76(45)