Triton-electron mass ratio

$mₜ/mₑ$ = 5496.921 535 51(21)

Value: 5496.921 535 51
Standard uncertainty: 2.1 × 10⁻⁷
Relative uncertainty: 3.8 × 10⁻¹¹ (38 parts per trillion)
Status: Measured
Symbol: $mₜ/mₑ$
Source: CODATA 2022 via NIST · NIST entry

Use in a calculation

# triton-electron mass ratio, CODATA 2022 (NIST)
triton_electron_mass_ratio = 5.49692153551e3  # standard uncertainty 2.1e-7

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

What it is

The mass of the triton 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).

Relative uncertainty

CODATA	Value (uncertainty)	Relative uncertainty	Change from previous
2022	5496.921 535 51(21)	3.8 × 10⁻¹¹	−0.8 σ of 2018
2018	5496.921 535 73(27)	4.9 × 10⁻¹¹	−0.6 σ of 2014
2014	5496.921 535 88(26)	4.7 × 10⁻¹¹	+1.8 σ of 2010
2010	5496.921 5267(50)	9.1 × 10⁻¹⁰	−0.0 σ of 2006
2006	5496.921 5269(51)	9.3 × 10⁻¹⁰

“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).