Alpha Particle Mass

The mass of a helium-4 nucleus, 4.0015 atomic mass units — the alpha of alpha decay.

Specifications & Metrics

symbol

mα

status

Measured — CODATA 2022 adjustment

value

6.644657345 × 10⁻²⁷ ± 2.1 × 10⁻³⁶ kg

Relative Scale in Constants

Core Principles & Analysis

• Equal to a helium atom minus two electron masses.
• About 3.97 GeV/c² of rest energy, the standard ejecta of heavy radioactive nuclei.
• Its great binding energy is why helium-4 is the universe's second most common nucleus.