- Value
- 1.6785 × 10−15
- Unit
- m
- Uncertainty
- 0.0021 × 10⁻¹⁵
- Copy-ready
1.6785e-15
The root-mean-square radius of the alpha particle's charge distribution.
Measured by laser spectroscopy of muonic helium; a benchmark for nuclear-structure calculations.
NIST, Fundamental Physical Constants — Complete Listing (2022 CODATA adjustment), retrieved 2026-07-26.
Compton wavelengths, radii and cross sections
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UsePhysics. "Alpha particle rms charge radius — 1.6785 × 10−15 m." UsePhysics.com. https://usephysics.com/reference/alpha-particle-rms-charge-radius. Value from the 2022 CODATA adjustment (NIST). Accessed [date].