Shielded proton gyromagnetic ratio in MHz/T

$γₚ′/2π$ = 42.576 385 43(17) MHz T⁻¹

Value: 42.576 385 43 MHz T⁻¹
Standard uncertainty: 1.7 × 10⁻⁷ MHz T⁻¹
Relative uncertainty: 4.0 × 10⁻⁹ (4 parts per billion)
Status: Measured
Symbol: $γₚ′/2π$
Source: CODATA 2022 via NIST · NIST entry

Use in a calculation

# shielded proton gyromagnetic ratio in MHz/T, CODATA 2022 (NIST)
shielded_proton_gyromagnetic_ratio_in_mh = 4.257638543e1  # MHz T^-1, standard uncertainty 1.7e-7

# SciPy: scipy.constants.physical_constants['shielded proton gyromag. ratio in MHz/T']

What it is

The precession frequency, per tesla of magnetic field, of a proton in a spherical sample of pure water at 25 °C, whose magnetic field is partly screened by the surrounding electrons: the gyromagnetic ratio divided by 2π. Magnetic resonance spectroscopists use this form.

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	42.576 385 43(17)	4.0 × 10⁻⁹	+1.5 σ of 2018
2018	42.576 384 74(46)	1.1 × 10⁻⁸	−0.6 σ of 2014
2014	42.576 385 07(53)	1.2 × 10⁻⁸	−1.5 σ of 2010
2010	42.576 3866(10)	2.3 × 10⁻⁸	−1.2 σ of 2006
2006	42.576 3881(12)	2.8 × 10⁻⁸	+0.2 σ of 2002
2002	42.576 3875(37)	8.7 × 10⁻⁸	−0.7 σ of 1998
1998	42.576 3888(18)	4.2 × 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).