Curie's Discovery

Alpha particle: nucleus of helium (2 p, 2 n)  4He22

Beta particle: speedy electron

Gamma radiation: bullets of light 

Photons with increasing energies:
       Radio Waves, Visible Light, X-Rays, Gamma rays

Experiment with Geiger counter and sources
  alpha particles: stopped by a sheet of paper
  beta particles: sheet of aluminum
  gamma radiation: a block of lead.
           penetrates far into a material
           disrupts chemical bonds

neutrons: discovered later, boiled off by a fissioning nucleus

Sadly, many years passed before scientists realized the perils of penetrating radiation