| Nature |
Helium nuclei (2 protons, 2 neutrons) |
High-energy electrons or positrons |
High-energy electromagnetic waves (photons) |
| Charge |
+2e (positive) |
-e (electrons) or +e (positrons) |
Neutral (0) |
| Mass |
~4 u (6.644 × 10⁻²⁷ kg) |
~1/1836 u (9.109 × 10⁻³¹ kg) |
Massless |
| Penetration Power |
Low (stopped by paper or a few cm of air) |
Moderate (stopped by a few mm of aluminum) |
High (requires several cm of lead or meters of concrete) |
| Ionization Ability |
High (strong interaction with matter) |
Moderate (less than alpha) |
Low (minimal interaction) |
| Speed |
~5-10% of speed of light (~1.5-3 × 10⁷ m/s) |
Up to 99% of speed of light (~3 × 10⁸ m/s) |
Speed of light (3 × 10⁸ m/s) |