ConstantID

Alpha particle rms charge radius

Atomic & nuclearMeasured

rα = 1.6785(21) × 10−15 m

Value
1.6785 × 10−15 m
Standard uncertainty
2.1 × 10−18 m
Relative uncertainty
1.3 × 10−3 (1251 parts per million)
Status
Measured
Symbol
rα
Source
CODATA 2022 via NIST · NIST entry

Use in a calculation

# alpha particle rms charge radius, CODATA 2022 (NIST)
alpha_particle_rms_charge_radius = 1.6785e-15  # m, standard uncertainty 2.1e-18

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

What it is

The root-mean-square radius of the electric charge distribution of the alpha particle, the nucleus of helium-4 (two protons and two neutrons).

In other units

UnitValue
CGS (cm)1.6785 × 10−13
pm picometre0.001 6785
fm femtometre1.6785

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.

History

First listed in CODATA 2022.

Related constants

Atomic & nuclear mα/me Alpha particle-electron mass ratio 7294.299 541 71(17) 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)