Deuteron rms charge radius

$r_d$ = 2.127 78(27) × 10⁻¹⁵ m

Value: 2.127 78 × 10⁻¹⁵ m
Standard uncertainty: 2.7 × 10⁻¹⁹ m
Relative uncertainty: 1.3 × 10⁻⁴ (127 parts per million)
Status: Measured
Symbol: $r_d$
Source: CODATA 2022 via NIST · NIST entry

Use in a calculation

# deuteron rms charge radius, CODATA 2022 (NIST)
deuteron_rms_charge_radius = 2.12778e-15  # m, standard uncertainty 2.7e-19

# SciPy: scipy.constants.physical_constants['deuteron rms charge radius']

What it is

The root-mean-square radius of the electric charge distribution of the deuteron, the nucleus of deuterium (one proton and one neutron).

In other units

Unit	Value
CGS (cm)	2.127 78 × 10⁻¹³
pm picometre	0.002 127 78
fm femtometre	2.127 78

Converted with ConstantID's unit table; digits are rounded to the precision of the value, and a long exact value is rounded only for display. The relative uncertainty is unchanged by conversion to an exactly defined unit.

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	2.127 78(27) × 10⁻¹⁵	1.3 × 10⁻⁴	−0.3 σ of 2018
2018	2.127 99(74) × 10⁻¹⁵	3.5 × 10⁻⁴	−5.3 σ of 2014
2014	2.1413(25) × 10⁻¹⁵	1.2 × 10⁻³	−0.5 σ of 2010
2010	2.1424(21) × 10⁻¹⁵	9.8 × 10⁻⁴	+0.8 σ of 2006
2006	2.1402(28) × 10⁻¹⁵	1.3 × 10⁻³	+0.3 σ of 2002
2002	2.1394(28) × 10⁻¹⁵	1.3 × 10⁻³

“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).