Question

Which one is more dangerous, alpha particles or beta particles?

Answer 1

Alpha particles are helium atoms, which are clearly bigger than electrons or positrons (beta particles). So, they are LESS dangerous to humans. (They penetrate less, but do more damage.)

They have a larger collision cross-section, so they have a shorter mean-free path. That is, they travel less far before they hit air molecules, and when they do, they fly away from humans.

As long as you're not dumb enough to swallow an alpha particle, you'll be fine!