ConstantID

Alpha particle-electron mass ratio

Atomic & nuclearMeasured

mα/me = 7294.299 541 71(17)

Value
7294.299 541 71
Standard uncertainty
1.7 × 10−7
Relative uncertainty
2.3 × 10−11 (23 parts per trillion)
Status
Measured
Symbol
mα/me
Source
CODATA 2022 via NIST · NIST entry

Use in a calculation

# alpha particle-electron mass ratio, CODATA 2022 (NIST)
alpha_particle_electron_mass_ratio = 7.29429954171e3  # standard uncertainty 1.7e-7

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

What it is

The mass of the alpha particle 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).

alpha particle-electron mass ratio: CODATA values 1998–2022 relative to the 2022 value, in parts per billion, with one-standard-uncertainty bars−7.5−5−2.50+2.5+5+7.5parts per billion1998200220062010201420182022

Relative uncertainty

alpha particle-electron mass ratio: relative standard uncertainty in each CODATA adjustment, logarithmic scale10⁻¹¹10⁻¹⁰10⁻⁹10⁻⁸1998200220062010201420182022
CODATAValue (uncertainty)Relative uncertaintyChange from previous
20227294.299 541 71(17)2.3 × 10−11 +1.2 σ of 2018
20187294.299 541 42(24)3.3 × 10−11 +0.2 σ of 2014
20147294.299 541 36(24)3.3 × 10−11 +1.8 σ of 2010
20107294.299 5361(29)4.0 × 10−10 −0.1 σ of 2006
20067294.299 5365(31)4.2 × 10−10 +0.1 σ of 2002
20027294.299 5363(32)4.4 × 10−10 +1.8 σ of 1998
19987294.299 508(16)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 mα Alpha particle mass 6.644 657 3450(21) × 10−27 kg Atomic & nuclear mαc2 Alpha particle mass energy equivalent 5.971 920 1997(19) × 10−10 J Atomic & nuclear mαc2 Alpha particle mass energy equivalent in MeV 3727.379 4118(12) MeV Atomic & nuclear mα Alpha particle mass in u 4.001 506 179 129(62) u Atomic & nuclear M(α) Alpha particle molar mass 4.001 506 1833(12) × 10−3 kg mol−1 Atomic & nuclear mα/mp Alpha particle-proton mass ratio 3.972 599 690 252(70) Atomic & nuclear Ar(α) Alpha particle relative atomic mass 4.001 506 179 129(62) Atomic & nuclear rα Alpha particle rms charge radius 1.6785(21) × 10−15 m