Helion g factor

$g_{h}$ = −4.255 250 6995(34)

Value: −4.255 250 6995
Standard uncertainty: 3.4 × 10⁻⁹
Relative uncertainty: 8.0 × 10⁻¹⁰ (799 parts per trillion)
Status: Measured
Symbol: $g_{h}$
Source: CODATA 2022 via NIST · NIST entry

Use in a calculation

# helion g factor, CODATA 2022 (NIST)
helion_g_factor = -4.2552506995  # standard uncertainty 3.4e-9

# SciPy: scipy.constants.physical_constants['helion g factor']

What it is

The g-factor of the helion, the nucleus of helium-3 (two protons and one neutron): the pure number that relates its magnetic moment to its spin angular momentum. A negative value means the moment points opposite to the spin.

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	−4.255 250 6995(34)	8.0 × 10⁻¹⁰	−1.7 σ of 2018
2018	−4.255 250 615(50)	1.2 × 10⁻⁸	+0.0 σ of 2014
2014	−4.255 250 616(50)	1.2 × 10⁻⁸	−0.1 σ of 2010
2010	−4.255 250 613(50)	1.2 × 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).