ConstantID

Proton charge to mass quotient

Atomic & nuclearMeasured

e/mp = 9.578 833 1430(30) × 107 C kg−1

Value
9.578 833 1430 × 107 C kg−1
Standard uncertainty
0.03 C kg−1
Relative uncertainty
3.1 × 10−10 (313 parts per trillion)
Status
Measured
Symbol
e/mp
Source
CODATA 2022 via NIST · NIST entry

Use in a calculation

# proton charge to mass quotient, CODATA 2022 (NIST)
proton_charge_to_mass_quotient = 9.578833143e7  # C kg^-1, standard uncertainty 0.03

# SciPy: scipy.constants.physical_constants['proton charge to mass quotient']

What it is

The proton's charge divided by its mass. It sets the cyclotron frequency of a proton in a magnetic field B: ω = (e/m_p)B.

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).

proton charge to mass quotient: CODATA values 1998–2022 relative to the 2022 value, in parts per billion, with one-standard-uncertainty bars−150−100−500+50+100+150parts per billion1998200220062010201420182022

Relative uncertainty

proton charge to mass quotient: relative standard uncertainty in each CODATA adjustment, logarithmic scale10⁻¹⁰10⁻⁹10⁻⁸10⁻⁷1998200220062010201420182022
CODATAValue (uncertainty)Relative uncertaintyChange from previous
20229.578 833 1430(30) × 1073.1 × 10−10 −4.5 σ of 2018
20189.578 833 1560(29) × 1073.0 × 10−10 −1.2 σ of 2014
20149.578 833 226(59) × 1076.2 × 10−9 −1.7 σ of 2010
20109.578 833 58(21) × 1072.2 × 10−8 −1.4 σ of 2006
20069.578 833 92(24) × 1072.5 × 10−8 +0.2 σ of 2002
20029.578 833 77(82) × 1078.6 × 10−8 −0.8 σ of 1998
19989.578 834 08(38) × 1074.0 × 10−8

“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,p Proton Compton wavelength 1.321 409 853 60(41) × 10−15 m Atomic & nuclear mp/me Proton–electron mass ratio 1836.152 673 426(32) Atomic & nuclear gp Proton g factor 5.585 694 6893(16) Atomic & nuclear γp Proton gyromagnetic ratio 2.675 221 8708(11) × 108 s−1 T−1 Atomic & nuclear γp/2π Proton gyromagnetic ratio in MHz/T 42.577 478 461(18) MHz T−1 Atomic & nuclear μp Proton magnetic moment 1.410 606 795 45(60) × 10−26 J T−1 Atomic & nuclear μp/μB Proton magnetic moment to Bohr magneton ratio 1.521 032 202 30(45) × 10−3 Atomic & nuclear μp/μN Proton magnetic moment to nuclear magneton ratio 2.792 847 344 63(82)